Parsing command-line arguments in C

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I m trying to write a program that can compare two files line by line  word by word  or character by character in C  It has to be able to read in command line options -l  -w  -i or --     if the option is -l  it compares the files line by line  if the option is -w  it compares the files word by word  if the option is --  it automatically assumes that the next argument is the first filename  if the option is -i  it compares them in a case insensitive manner  defaults to comparing the files character by character   It s not supposed to matter how many times the options are input as long as -w and -l aren t inputted at the same time and there are no more or less than two files  I don t even know where to begin with parsing the command line arguments  So this is the code that I came up with for everything  I haven t error checked it quite yet  but am I writing things in an overcomplicated manner        Functions to compare files      int compare line    int compare word    int compare char    int case insens           Program to compare the information in two files and print message saying    whether or not this was successful      int main int argc  char  argv             Loop counter        size t i   0          Variables for functions        int caseIns   0      int line   0      int word   0          File pointers        FILE  fp1   fp2                 Read through command-line arguments for options              for  i   1  i  lt  argc  i                  printf  quot argv  u     s n quot   i  argv i            if  argv i  0      -                          if  argv i  1      i                                   caseIns   1                              if  argv i  1      l                                   line   1                              if  argv i  1      w                                   word   1                              if  argv i  1      -                                   fp1   argv i  2                    fp2   argv i  3                               else                                 printf  quot Invalid option  quot                     return 2                                   else                      fp1 argv i               fp2 argv i  1                                   Check that files can be opened              if   fp1   fopen fp1   quot rb quot        NULL       fp2   fopen fp2   quot rb quot       NULL                 perror  quot fopen   quot            return 3            else               if  caseIns    1                        if line    1  amp  amp  word    1                                printf  quot That is invalid  quot                    return 2                            if line    1  amp  amp  word    0                                if compare line case insens fp1  fp2      0                          return 0                            if line    0  amp  amp  word    1                                if compare word case insens fp1  fp2      0                      return 0                            else                               if compare char case insens fp1 fp2      0                      return 0                                  else                       if line    1  amp  amp  word    1                                printf  quot That is invalid  quot                    return 2                            if line    1  amp  amp  word    0                                if compare line fp1  fp2     0                      return 0                            if line    0  amp  amp  word    1                                if compare word fp1  fp2     0                      return 0                            else                               if compare char fp1  fp2     0                      return 0                                    return 1       if   fp1   fclose fp1      NULL        fp2   fclose fp2      NULL                  perror  quot fclose   quot            return 3            else               fp1   fclose fp1           fp2   fclose fp2                  Function to compare two files line-by-line      int compare line FILE  fp1  FILE  fp2           Buffer variables to store the lines in the file        char buff1  LINESIZE       char buff2  LINESIZE           Check that neither is the end of file        while   feof fp1    amp  amp    feof fp2                     Go through files line by line            fgets buff1  LINESIZE  fp1           fgets buff2  LINESIZE  fp2                 Compare files line by line        if strcmp buff1  buff2     0                printf  quot Files are equal  n quot            return 0            printf  quot Files are not equal  n quot        return 1           Function to compare two files word-by-word      int compare word FILE  fp1  FILE  fp2           File pointers        FILE  fp1   fp2          Arrays to store words        char fp1words LINESIZE       char fp2words LINESIZE        if strtok fp1   quot   quot      NULL    strtok fp2   quot   quot      NULL                printf  quot File is empty  Cannot compare  n quot            return 0            else               fp1words   strtok fp1   quot   quot            fp2words   strtok fp2   quot   quot             if fp1words    fp2words                        fputs fp1words               fputs fp2words               printf  quot Files are equal  n quot                return 0                      return 1           Function to compare two files character by character      int compare char FILE  fp1 FILE  fp2           Variables to store the characters from both files        int c      int d          Buffer variables to store chars        char buff1  LINESIZE       char buff2  LINESIZE        while   c   fgetc fp1     EOF   amp  amp     d   fgetc fp2    EOF                  if c    d                        if  fscanf fp1   quot  c quot   buff1       fscanf fp2   quot  c quot   buff2                                  printf  quot Files have equivalent characters  n quot                    return 1                  break                                     return 0           Function to compare two files in a case-insensitive manner      int case insens FILE  fp1  FILE  fp2  size t n           Pointers for files         FILE  fp1   fp2          Variable to go through files         size t i   0          Arrays to store file information         char fp1store LINESIZE       char fp2store LINESIZE        while  feof fp1   amp  amp   feof fp2                 for i   0  i  lt  n  i                          fscanf fp1   quot  s quot   fp1store               fscanf fp2   quot  s quot   fp2store                fp1store   tolower fp1store               fp2store   tolower fp2store                return 1                      return 0

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Google s gflags

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You can use James Theiler s  quot opt quot  package  And a flattering post with some examples of how it is so much simpler than other approaches is here  Opt 3 19 review and upgrades

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Tooting my own horn if I may  I d also like to suggest taking a look at an option parsing library that I ve written  dropt    It s a C library  with a C   wrapper if desired   It s lightweight  It s extensible  custom argument types can be easily added and have equal footing with built-in argument types   It should be very portable  it s written in standard C  with no dependencies  other than the C standard library   It has a very unrestrictive license  zlib libpng     One feature that it offers that many others don t is the ability to override earlier options   For example  if you have a shell alias   alias bar  foo --flag1 --flag2 --flag3    and you want to use bar but with--flag1 disabled  it allows you to do   bar --flag1 0

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for  int i   1  i  lt  argc  i           if  strcmp argv i   -i    0            filename   argv i 1           printf  filename   s  filename         else if  strcmp argv i   -c    0            convergence   atoi argv i   1            printf   nconvergence   d  convergence         else if  strcmp argv i   -a    0            accuracy   atoi argv i   1            printf   naccuracy  d  accuracy         else if  strcmp argv i   -t    0            targetBitRate   atof argv i   1            printf   ntargetBitRate  f  targetBitRate         else if  strcmp argv i   -f    0            frameRate   atoi argv i   1            printf   nframeRate  d  frameRate

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Docopt has a C implementation that I thought was quite nice  From a man-page standardized format describing command line options  docopt infers and creates an argument parser  This got started in Python  the Python version literally just parses the docstring and returns a dict  To do this in C takes a little more work  but it s clean to use and has no external dependencies

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It s a bit too big to include in a Stack Overflow answer  but I made a library for defining commands lines declaratively   It takes advantage of the the C  14 ability to build up a class constructor by giving initial values to each member variable   The library is mostly a base class   To define your command syntax  you declare a struct that derives from it   Here s a sample   struct MyCommandLine   public core  CommandLine       Argument lt std  string gt  m verb this   program    program exe            this is what my program does        Option lt bool gt  m help this   help   false           displays information about the command line        Alias lt bool gt  alias help this        amp m help       Option lt bool gt  m demo this   demo   false           runs my program in demonstration mode        Option lt bool gt  m maximize this   maximize   false           opens the main window maximized        Option lt int gt  m loops this   loops   1           specifies the number of times to repeat        EnumOption lt int gt  m size this   size   3                                 s   1                                  small   1                                  m   3                                  med   3                                  medium   3                                  l   5                                  large   5           BeginOptionalArguments here this       Argument lt std  string gt  m file this   file-name                name of an existing file to open      cl    The Argument  Option  and Alias class templates are declared in the scope of the CommandLine base class  and you can specialize them for your own types   Each one takes the this pointer  the option name  the default value  and a description for use in printing the command synopsis usage   I m still looking to eliminate the need to sprinkle all the this pointers in there  but I haven t found a way to do it without introducing macros   Those pointers allow each member to register itself with the tables in the base class that drive the parsing   Once you have an instance  there are several overloads of a method to parse the input from a string or a main-style argument vector   The parser handles both Windows-style and Unix-style option syntax   if   cl Parse argc  argv         std  string message      for  const auto  amp error   cl GetErrors              message    error     n             std  cerr  lt  lt  message      exit EXIT FAILURE       Once it s parsed  you can access the value of any of the options using operator     if  cl m help      std  cout  lt  lt  cl GetUsage      for  int i   0  i  lt  cl m loops      i            The whole library is only about 300 lines  excluding tests    The instances are a bit bloaty  since the parsing tables are part of the instance  rather than the class    But you generally only need one instance per program  and the convenience of this purely declarative approach is pretty powerful  and an instance can be reset simply by parsing new input

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A command is basically a string  In general it can be split into two parts - the command s name and the command s arguments   Example   ls   is used for listing the contents of a directory   user computer    ls Documents Pictures Videos       The ls above is executed inside home folder of a user  Here the argument which folder to list is implicitly added to the command  We can explicitly pass some arguments   user computer    ls Picture image1 jpg image2 jpg       Here I have explicitly told ls which folder s contents I d like to see  We can use another argument for example l for listing the details of each file and folder such as access permissions  size etc    user computer    ls Pictures -rw-r--r-- 1 user user   215867 Oct 12  2014 image1 jpg -rw-r--r-- 1 user user   268800 Jul 31  2014 image2 jpg       Oh  the size looks really weird  215867  268800   Let s add the h flag for human-friendly output   user computer    ls -l -h Pictures -rw-r--r-- 1 user user  211K Oct 12  2014 image1 jpg -rw-r--r-- 1 user user  263K Jul 31  2014 image2 jpg       Some commands allow their arguments to be combined  in the above case we might as well write ls -lh and we ll get the same output   using short  a single letter usually but sometimes more  abbreviation  or long names  in case of ls we have the -a or --all for listing all files including hidden ones with --all being the long name for -a  etc  There are commands where the order of the arguments is very important but there are also others where the order of the arguments is not important at all   For example it doesn t matter if I use ls -lh or ls -hl however in the case of mv  moving renaming files  you have less flexibility for your last 2 arguments that is mv  OPTIONS  SOURCE DESTINATION   In order to get a grip of commands and their arguments you can use man  example  man ls  or info  example  info ls    In many languages including C C   you have a way of parsing command line arguments that the user has attached to the call of the executable  the command   There are also numerous libraries available for this task since in its core it s actually not that easy to do it properly and at the same time offer a large amount of arguments and their varieties    getopt argp parse gflags       Every C C   application has the so called entry point  which is basically where your code starts - the main function   int main  int argc  char  argv         When you launch your application the first line of code that is ran is this one - entry point        Some code here     return 0     Exit code of the application - exit point     No matter if you use a library  like one of the above I ve mentioned  but this is clearly not allowed in your case     or do it on your own your main function has the two arguments    argc - represents the number of arguments argv - a pointer to an array of strings  you can also see char   argv which is basically the same but more difficult to use     NOTE  main actually also has a third argument char  envp   which allows passing environment variables to your command but this is a more advanced thing and I really don t think that it s required in your case   The processing of command line arguments consists of two parts    Tokenizing - this is the part where each argument gets a meaning  Its the process of breaking your arguments list into meaningful elements  tokens   In the case of ls -l the l is not only a valid character but also a token in itself since it represents a complete  valid argument    Here is an example how to output the number of arguments and the  unchecked for validity  characters that may or may not actually be arguments    include  lt iostream gt  using std  cout  using std  endl   int main  int argc  char  argv          cout  lt  lt   Arguments  count  d   lt  lt  argc  lt  lt  endl          First argument is ALWAYS the command itself     cout  lt  lt   Command     lt  lt  argv 0   lt  lt  endl          For additional arguments we start from argv 1  and continue  if any      for  int i   1  i  lt  argc  i              cout  lt  lt   arg    lt  lt  i  lt  lt         lt  lt  argv i   lt  lt  endl             cout  lt  lt  endl      return 0       Parsing - after acquiring the tokens  arguments and their values  you need to check if your command supports these  For example   user computer    ls -y   will return  ls  invalid option --  y  Try  ls --help  for more information    This is because the parsing has failed  Why  Because y  and -y respectively  note that -  --    etc  is not required and its up to the parsing of the arguments whether you want that stuff there or not  in Unix Linux systems this is a sort of a convention but you are not bind to it  is an unknown argument for the ls command    For each argument  if successfully recognized as such  you trigger some sort of change in your application  You can use an if-else for example to check if a certain argument is valid and what it does followed by changing whatever you want that argument to change in the execution of the rest of your code  You can go the old C-style or C  -style      if  strcmp argv 1    x      0           - compare the pointer value    if  std  string argv 1       x            - convert to string and then compare   I actually like  when not using a library  to convert argv to an std  vector of strings like this   std  vector lt std  string gt  args argv  argv argc   for  size t i   1  i  lt  args size      i        if  args i      x                Handle x           else if  args i      y                Handle y                      The std  vector lt std  string gt  args argv  argv argc   part is just an easier C  -ish way to handle the array of strings since char   is a C-style string  with char  argv   being an array of such strings  which can easily be converted to a C   string that is std  string  Then we can add all converted strings to a vector by giving the starting address of argv and then also pointing to its last address namely argv   argc  we add argc number of string to the base address of argv which is basically pointing at the last address of our array    Inside the for loop above you can see that I check  using simple if-else  if a certain argument is available and if yes then handle it accordingly  A word of caution  by using such a loop the order of the arguments doesn t matter  As I ve mentioned at the beginning some commands actually have a strict order for some or all of their arguments  You can handle this in a different way by manually calling the content of each args  or argv if you use the initial char  argv   and not the vector solution       No for loop  if  args 1      x            Handle x   else if  args 2      y            Handle y            This makes sure that at position 1 only the x will be expected etc  The problem with this is that you can shoot yourself in the leg by going out of bounds with the indexing so you have to make sure that your index stays within the range set by argc   if  argc  gt  1  amp  amp  argc  lt   3        if  args 1      x                Handle x           else if  args 2      y                Handle y           The example above makes sure you have content at index 1 and 2 but not beyond   Last but not least the handling of each argument is a thing that is totally up to you  You can use boolean flags that are set when a certain argument is detected  example  if  args i      x     xFound   true    and later on in your code do something based on the bool xFound and its value   numerical types if the argument is a number OR consists of number along with the argument s name  example  mycommand -x 4 has an argument -x 4 which you can additionally parse as x and 4 the last being the value of x  etc  Based on the task at hand you can go crazy and add an insane amount of complexity to your command line arguments   Hope this helps  Let me know if something is unclear or you need more examples

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I have used GetPot for some projects  http   getpot sourceforge net  Main feature  everything is in a single header file  no build hassles  Just save it somewhere on your machine and  quot  include quot  it in your file holding main   Hasn t be updated recently  but it is nicely documented  and works well

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argstream is quite similar to boost program option  it permits to bind variables to options  etc  However it does not handle options stored in a configuration file

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I think that GNU GetOpt is not too immediate to use   Qt and Boost could be a solution  but you need to download and compile a lot of code   So I implemented a parser by myself that produces a std  map lt std  string  std  string  of parameters   For example  calling      myProgram -v -p 1234   map will be      -v          -p    1234     Usage is   int main int argc  char  argv          MainOptions mo argc  argv       MainOptions  Option  opt   mo getParamFromKey  -p        const string type   opt     opt  second           cout  lt  lt  type  lt  lt  endl     Prints 1234           Your check code        MainOptions h   ifndef MAINOPTIONS H   define MAINOPTIONS H    include  lt map gt   include  lt string gt   class MainOptions   public      typedef std  pair lt std  string  std  string gt  Option      MainOptions int argc  char  argv         virtual  MainOptions        std  string getAppName   const      bool hasKey const std  string amp   const      Option  getParamFromKey const std  string amp   const      void printOptions   const  private      typedef std  map lt std  string  std  string gt  Options      void parse        const char  const  begin   const      const char  const  end   const      const char  const  last   const      Options options       int argc       char   argv       std  string appName        MainOptions cpp   include  MainOptions h    include  lt iostream gt   using namespace std   MainOptions  MainOptions int argc  char  argv              argc  argc           argv  argv        appName    argv  0       this- gt parse       MainOptions   MainOptions        std  string MainOptions  getAppName   const       return appName      void MainOptions  parse         typedef pair lt string  string gt  Option      Option  option   new pair lt string  string gt         for  const char  const   i   this- gt begin     1  i    this- gt end    i              const string p    i          if  option- gt first        amp  amp  p 0      -                 option- gt first   p              if  i    this- gt last                      options  insert Option option- gt first  option- gt second                              continue            else if  option- gt first        amp  amp  p 0      -                 option- gt second    null      or leave empty                 options  insert Option option- gt first  option- gt second                option- gt first   p              option- gt second                   if  i    this- gt last                      options  insert Option option- gt first  option- gt second                              continue            else if  option- gt first                      option- gt second   p              options  insert Option option- gt first  option- gt second                option- gt first                   option- gt second                   continue                     void MainOptions  printOptions   const       std  map lt std  string  std  string gt   const iterator m   options  begin        int i   0      if  options  empty              cout  lt  lt   No parameters n             for    m    options  end    m      i            cout  lt  lt   Parameter     lt  lt  i  lt  lt         lt  lt    m  first  lt  lt       lt  lt    m  second                  lt  lt     n            const char  const  MainOptions  begin   const       return argv      const char  const  MainOptions  end   const       return argv    argc      const char  const  MainOptions  last   const       return argv    argc  - 1     bool MainOptions  hasKey const std  string amp  key  const       return options  find key     options  end       MainOptions  Option  MainOptions  getParamFromKey          const std  string amp  key  const       const Options  const iterator i   options  find key       MainOptions  Option  o   0      if  i    options  end              o   new MainOptions  Option   i  first    i  second             return o

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There are a number of good libraries available    Boost Program Options is a fairly heavyweight solution  both because adding it to your project requires you to build boost  and the syntax is somewhat confusing  in my opinion   However  it can do pretty much everything including having the command line options override those set in configuration files   SimpleOpt is a fairly comprehensive but simple command line processor  It is a single file and has a simple structure  but only handles the parsing of the command line into options  you have to do all of the type and range checking  It is good for both Windows and Unix and comes with a version of glob for Windows too   getopt is available on Windows  It is the same as on Unix machines  but it is often a GPL library

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You could use an already created library for this  http   www boost org doc libs 1 44 0 doc html program options html

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I wrote a tiny library that parses arguments similar to POpt  which I had several issues with  called XOpt  It uses GNU-style argument parsing and has a very similar interface to POpt  I use it from time to time with great success  and it works pretty much anywhere

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AnyOption is a C   class for easy parsing of complex commandline options  It also parses options from a rsourcefile in option value pair format    AnyOption implements the traditional POSIX style character options   -n   as well as the newer GNU style long options   --name    Or you can use a simpler long option version   -name   by asking to ignore the POSIX style options

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Try CLPP library  It s simple and flexible library for command line parameters parsing  Header-only and cross-platform  Uses ISO C   and Boost C   libraries only  IMHO it is easier than Boost Program options   Library  http   sourceforge net projects clp-parser  26 October 2010 - new release 2 0rc  Many bugs fixed  full refactoring of the source code  documentation  examples and comments have been corrected

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if this is linux unix then the standard one to use is gnu getopt  http   www gnu org s libc manual html node Getopt html

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You could try my little options header  166 loc so easily hackable  options hpp  It is a single header implementation and should do what you ask  It also prints you the help page automatically

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I am using getopt   under windows mingw    while   c   getopt myargc  myargv   vp d rcx       -1            switch  c            case  v      print version             printf   s Version  s n   myargv 0   VERSION               exit 0               break          case  p      change local port to listen to             strncpy g portnum  optarg  10               break

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I can suggest Templatized C   Command Line Parser Library  some forks on GitHub are available   the API is very straightforward and  cited from the site       the library is implemented entirely in header files making it easy to   use and distribute with other software  It is licensed under the MIT   License for worry free distribution    This is an example from the manual  colored here for simplicity    include  lt string gt   include  lt iostream gt   include  lt algorithm gt   include  lt tclap CmdLine h gt   int main int argc  char   argv            Wrap everything in a try block   Do this every time         because exceptions will be thrown for problems      try           Define the command line object  and insert a message        that describes the program  The  Command description message         is printed last in the help text  The second argument is the        delimiter  usually space  and the last one is the version number         The CmdLine object parses the argv array based on the Arg objects        that it contains      TCLAP  CmdLine cmd  Command description message         0 9            Define a value argument and add it to the command line         A value arg defines a flag and a type of value that it expects         such as  -n Bishop       TCLAP  ValueArg lt std  string gt  nameArg  n   name   Name to print  true  homer   string            Add the argument nameArg to the CmdLine object  The CmdLine object        uses this Arg to parse the command line      cmd add  nameArg            Define a switch and add it to the command line         A switch arg is a boolean argument and only defines a flag that        indicates true or false   In this example the SwitchArg adds itself        to the CmdLine object as part of the constructor   This eliminates        the need to call the cmd add   method   All args have support in        their constructors to add themselves directly to the CmdLine object         It doesn t matter which idiom you choose  they accomplish the same thing      TCLAP  SwitchArg reverseSwitch  r   reverse   Print name backwards   cmd  false           Parse the argv array      cmd parse  argc  argv            Get the value parsed by each arg      std  string name   nameArg getValue        bool reverseName   reverseSwitch getValue            Do what you intend      if   reverseName                     std  reverse name begin   name end                 std  cout  lt  lt   My name  spelled backwards  is     lt  lt  name  lt  lt  std  endl            else             std  cout  lt  lt   My name is     lt  lt  name  lt  lt  std  endl          catch  TCLAP  ArgException  amp e      catch any exceptions       std  cerr  lt  lt   error     lt  lt  e error    lt  lt    for arg    lt  lt  e argId    lt  lt  std  endl

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A simple solution is to put argv into a std  map for easy lookups  map lt string  string gt  argvToMap int argc  char   argv          map lt string  string gt  args       for int i 1  i lt argc  i              if  argv i  0      -                 const string key   argv i               string value    quot  quot               if  i 1  lt  argc  amp  amp  argv i 1  0      -                     value   string argv i 1                    i                               args key    value                       return args     Example usage   include  lt map gt   include  lt string gt   include  lt iostream gt   using namespace std   map lt string  string gt  argvToMap int argc  char   argv          map lt string  string gt  args       for int i 1  i lt argc  i              if  argv i  0      -                 const string key   argv i               string value    quot  quot               if  i 1  lt  argc  amp  amp  argv i 1  0      -                     value   string argv i 1                    i                               args key    value                       return args     void printUsage         cout  lt  lt   quot simple args  A sample program for simple arg parsing n quot               quot  n quot               quot Example usage  n quot               quot       simple args --print-all --option 1 --flag 2 n quot      int main int argc  char   argv          auto args   argvToMap argc  argv        if  args count  quot -h quot      args count  quot --help quot              printUsage              else if  args count  quot --print-all quot              for  auto const  amp  pair  args              cout  lt  lt   quot   quot   lt  lt  pair first  lt  lt   quot    quot   lt  lt  pair second  lt  lt   quot   n quot              return 0     Output      simple args --print-all --option 1 --flag  quot hello world quot   --flag  hello world   --option  1   --print-all     There are definitely significant limitations to this approach  but I found it struck a good balance of simplicity and utility

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The suggestions for boost  program options and GNU getopt are good ones   However  for simple command line options I tend to use std  find  For example  to read the name of a file after a -f command line argument   You can also just detect if a single-word option has been passed in like -h for help    include  lt algorithm gt   char  getCmdOption char    begin  char    end  const std  string  amp  option        char    itr   std  find begin  end  option       if  itr    end  amp  amp    itr    end                return  itr            return 0     bool cmdOptionExists char   begin  char   end  const std  string amp  option        return std  find begin  end  option     end     int main int argc  char   argv          if cmdOptionExists argv  argv argc   -h                     Do stuff            char   filename   getCmdOption argv  argv   argc   -f         if  filename                   Do interesting things                           return 0      On thing to look out for with this approach you must use std  strings as the value for std  find otherwise the equality check is performed on the pointer values      I hope it is okay to edit this response instead adding a new one  as this is based on the original answer  I re-wrote the functions slightly and encapsulated them in a class  so here is the code  I thought it might be practical to use it that way as well   class InputParser      public          InputParser  int  amp argc  char   argv               for  int i 1  i  lt  argc    i                  this- gt tokens push back std  string argv i                            author iain         const std  string amp  getCmdOption const std  string  amp option  const              std  vector lt std  string gt   const iterator itr              itr    std  find this- gt tokens begin    this- gt tokens end    option               if  itr    this- gt tokens end    amp  amp    itr    this- gt tokens end                     return  itr                            static const std  string empty string                  return empty string                         author iain         bool cmdOptionExists const std  string  amp option  const              return std  find this- gt tokens begin    this- gt tokens end    option                        this- gt tokens end                  private          std  vector  lt std  string gt  tokens      int main int argc  char   argv       InputParser input argc  argv       if input cmdOptionExists  -h                Do stuff           const std  string  amp filename   input getCmdOption  -f        if   filename empty                Do interesting things               return 0

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Okay  that s the start of long story - made short abort parsing a command line in C           Helper function to parse the command line    param argc Argument Counter    param argv Argument Vector    param prog Program Instance Reference to fill with options    bool parseCommandLine int argc  char  argv    DuplicateFileHardLinker  prog      bool pathAdded   false        Iterate over all arguments      for  int i   1  i lt argc  i              Is argv a command line option      if  argv i  0      -     argv i  0                             Optionally Cut that part vvvvvvvvvvvvv for sake of simplicity                  Check for longer options       if  stricmp   amp argv i  1    quot NoFileName quot      0               strcmp   amp argv i  1    quot q1 quot               0              boNoFileNameLog   true           else if  strcmp   amp argv i  1    quot HowAreYou  quot      0               logInfo   quot SECRET FOUND  Well - wow I m glad ya ask me  quot            else                                                                                                        Now here comes the main thing                         Check for one-character options         while  char option      argv i                switch  option              case                     Show program usage              logInfo L quot Options  quot                logInfo L quot    q t gt Quite mode quot                logInfo L quot    v t gt Verbose mode quot                logInfo L quot    d t gt Debug mode quot                return false                  Log options           case  q               setLogLevel LOG ERROR               break             case  v               setLogLevel LOG VERBOSE               break             case  d               setLogLevel LOG DEBUG               break             default              logError L quot   s  is an illegal command line option  quot                         quot   Use    to see valid options  quot   option               return false                 switch one-char-option              while one-char-options             else one vs longer options          if isArgAnOption                                             So that s it                                          What follows now is are some useful extras               else             The command line options seems to be a path          WCHAR tmpPath MAX PATH LENGTH         mbstowcs tmpPath  argv i   sizeof tmpPath              Check if the path is existing                     prog- gt addPath tmpPath      Comment or remove to get a working example       pathAdded   true                  Check for parameters   if   pathAdded        logError  quot You need to specify at least one folder to process  n quot                quot Use    to see valid options  quot        return false         return true      int main int argc  char  argv         try          Parse the command line     if    parseCommandLine argc  argv  prog            return 1                I know that sample is just to show how the nicely parse command-line arguments        So Please excuse more nice useful C-glatter that follows now           catch   LPCWSTR err         DWORD dwError   GetLastError        if   wcslen err   gt  0           if   dwError    0             logError dwError  err                 else           logError err                     return 2          define LOG ERROR                1  define LOG INFO                 0  define LOG VERBOSE             -1  define LOG DEBUG               -2      Logging level for the console output    int logLevel   LOG INFO   void logError LPCWSTR message           va list argp    fwprintf stderr  L quot ERROR   quot      va start argp  message     vfwprintf stderr  message  argp     va end argp     fwprintf stderr  L quot  n quot        void logInfo LPCWSTR message           if   logLevel  lt   LOG INFO         va list argp      va start argp  message       vwprintf message  argp       va end argp       wprintf L quot  n quot           Note that this version will also support combining arguments  So instead of writing  h  s - gt   hs will also work  Sorry for being the n-th person posting here - however I wasn t really satisfied with all the stand-alone-versions I saw here  Well  the library ones are quiet nice  So I would prefer the libUCW option parser  Arg or Getopt over a home-made ones  Note you may change     argv i  - gt     argv   0  It is longer and less cryptic  but still cryptic  Okay  let s break it down   argv i - gt  access i-th element in the argv-char pointer field            - gt  will forward the argv-pointer by one char       0 - gt  will follow the pointer read the char            - gt  bracket are there so we ll increase the pointer and not the char value itself    It is so nice that in C   the pointers  died  - long live the pointers

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Try Boost  Program Options  It allows you to read and parse command lines as well as config files

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If you just want to process command line options yourself  the easiest way is to put   vector lt string gt  args argv   1  argv   argc     at the top of your main     This copies all command-line arguments into a vector of std  strings   Then you can use    to compare strings easily  instead of endless strcmp   calls   For example   int main int argc  char   argv        vector lt string gt  args argv   1  argv   argc       string infname  outfname          Loop over command-line args         Actually I usually use an ordinary integer loop variable and compare        args i  instead of  i -- don t tell anyone         for  auto i   args begin    i    args end      i            if   i     -h      i     --help                 cout  lt  lt   Syntax  foomatic -i  lt infile gt  -o  lt outfile gt    lt  lt  endl              return 0            else if   i     -i                 infname      i            else if   i     -o                 outfname      i                       EDIT  I realised I was copying argv 0   the name of the program  into args -- fixed

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I like C s getopt    but then I m old    -

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There is a great general-purpose C library  libUCW  which includes neat command-line option parsing and configuration file loading  The library also comes with good documentation and includes some other useful stuff  fast I O  data structures  allocators       but this can be used separately  Example libUCW option parser  from the library docs   include  lt ucw lib h gt   include  lt ucw opt h gt   int english  int sugar  int verbose  char  tea name   static struct opt section options       OPT ITEMS       OPT HELP  quot A simple tea boiling console  quot        OPT HELP  quot Usage  teapot  options  name-of-the-tea quot        OPT HELP  quot  quot        OPT HELP  quot Options  quot        OPT HELP OPTION      OPT BOOL  e    quot english-style quot   english  0   quot  tEnglish style  with milk  quot        OPT INT  s    quot sugar quot   sugar  OPT REQUIRED VALUE   quot  lt spoons gt  tAmount of sugar  in teaspoons  quot        OPT INC  v    quot verbose quot   verbose  0   quot  tVerbose  the more -v  the more verbose  quot        OPT STRING OPT POSITIONAL 1   NULL  tea name  OPT REQUIRED   quot  quot        OPT END         int main int argc  char   argv      opt parse  amp options  argv 1     return 0

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Boost Program options

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Qt 5 2 comes with a command line parser API   Small example    include  lt QCoreApplication gt   include  lt QCommandLineParser gt   include  lt QDebug gt   int main int argc  char   argv      QCoreApplication app argc  argv     app setApplicationName  ToolX      app setApplicationVersion  1 2       QCommandLineParser parser    parser setApplicationDescription  Tool for doing X       parser addHelpOption      parser addVersionOption      parser addPositionalArgument  infile         QCoreApplication  translate  main    Input file         QCommandLineOption verbose opt            QCoreApplication  translate  main    be verbose       parser addOption verbose opt      QCommandLineOption out opt QStringList    lt  lt   o   lt  lt   output         QCoreApplication  translate  main    Output file           QCoreApplication  translate  main    filename       value name       QCoreApplication  translate  main    out        default value            parser addOption out opt         exits on error   parser process app      const QStringList args   parser positionalArguments       qDebug    lt  lt   Input files     lt  lt  args      lt  lt     verbose     lt  lt  parser isSet verbose opt       lt  lt     output     lt  lt  parser value out opt       lt  lt    n     return 0      Example output  The automatically generated help screen        qtopt -h Usage    qtopt  options  infile Tool for doing X   Options    -h  --help               Displays this help    -v  --version            Displays version information    -                        be verbose   -o  --output   Output file   Arguments    infile                   Input file    Automatically generated version output        qtopt -v ToolX 1 2   Some real calls        qtopt b1 -  -o tmp blah foo Input files     b1    blah foo     verbose   true   output    tmp      qtopt           Input files        verbose   false   output    out    A parse error        qtopt --hlp Unknown option  hlp     echo    1   Conclusion  If your program already use the Qt     5 2  libraries  its command line parsing API is convenient enough to get the job done   Be aware that builtin Qt options are consumed by QApplication before the option parser runs

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If you don t want to use boost  I d recommend this little helper class

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To my knowledge  the three most popular ways how to parse command line arguments in C are    Getopt   include  lt unistd h gt  from the POSIX C Library   which can solve simple argument parsing tasks  If you re a bit familiar with bash  the getopt built-in of bash is based on Getopt from the GNU libc  Argp   include  lt argp h gt  from the GNU C Library   which can solve more complex tasks and takes care of stuff like  for example   -   --help for help message  including email address -V  --version for version information --usage for usage message  Doing it yourself  which I don t recommend for programs that would be given to somebody else  as there is too much that could go wrong or lower quality  The popular mistake of forgetting about  --  to stop option parsing is just one example    The GNU C Library documentation has some nice examples for Getopt and Argp    http   www gnu org software libc manual html node Getopt html http   www gnu org software libc manual html node Argp html   Example for using Getopt   include  lt stdbool h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt unistd h gt   int main int argc  char  argv          bool isCaseInsensitive   false      int opt      enum   CHARACTER MODE  WORD MODE  LINE MODE   mode   CHARACTER MODE       while   opt   getopt argc  argv   ilw       -1            switch  opt            case  i   isCaseInsensitive   true  break          case  l   mode   LINE MODE  break          case  w   mode   WORD MODE  break          default              fprintf stderr   Usage   s  -ilw   file     n   argv 0                exit EXIT FAILURE                           Now optind  declared extern int by  lt unistd h gt   is the index of the first non-option argument         If it is  gt   argc  there were no non-option arguments                  Example for using Argp   include  lt argp h gt   include  lt stdbool h gt   const char  argp program version    programname programversion   const char  argp program bug address     lt your email address gt    static char doc      Your program description    static char args doc       FILENAME       static struct argp option options               line    l   0  0   Compare lines instead of characters            word    w   0  0   Compare words instead of characters            nocase    i   0  0   Compare case insensitive instead of case sensitive           0        struct arguments       enum   CHARACTER MODE  WORD MODE  LINE MODE   mode      bool isCaseInsensitive      static error t parse opt int key  char  arg  struct argp state  state        struct arguments  arguments   state- gt input      switch  key        case  l   arguments- gt mode   LINE MODE  break      case  w   arguments- gt mode   WORD MODE  break      case  i   arguments- gt isCaseInsensitive   true  break      case ARGP KEY ARG  return 0      default  return ARGP ERR UNKNOWN               return 0     static struct argp argp     options  parse opt  args doc  doc  0  0  0     int main int argc  char  argv          struct arguments arguments       arguments mode   CHARACTER MODE      arguments isCaseInsensitive   false       argp parse  amp argp  argc  argv  0  0   amp arguments                   Example for Doing it Yourself   include  lt stdbool h gt   include  lt stdio h gt   include  lt stdlib h gt   int main int argc  char  argv             bool isCaseInsensitive   false      enum   CHARACTER MODE  WORD MODE  LINE MODE   mode   CHARACTER MODE      size t optind      for  optind   1  optind  lt  argc  amp  amp  argv optind  0      -   optind              switch  argv optind  1             case  i   isCaseInsensitive   true  break          case  l   mode   LINE MODE  break          case  w   mode   WORD MODE  break          default              fprintf stderr   Usage   s  -ilw   file     n   argv 0                exit EXIT FAILURE                                  argv points to the remaining non-option arguments         If  argv is NULL  there were no non-option arguments                     Disclaimer  I am new to Argp  the example might contain errors

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Boost Program options

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Try CLPP library  It s simple and flexible library for command line parameters parsing  Header-only and cross-platform  Uses ISO C   and Boost C   libraries only  IMHO it is easier than Boost Program options   Library  http   sourceforge net projects clp-parser   26 October 2010 - new release 2 0rc  Many bugs fixed  full refactoring of the source code  documentation  examples and comments have been corrected

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With C    the answer is usually in Boost     Boost Program Options

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And there s a Google library available   Really  command-line parsing is  solved    Just pick one

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Yet another alternative is The Lean Mean C   Option Parser   http   optionparser sourceforge net             It is a header-only library  just a single header file  in fact  and unlike all the other suggestions it is  also freestanding  i e  it has no dependencies whatsoever  In particular there s no dependency on the STL  It does not even use exceptions or anything else that requires library support  This means it can be linked with plain C or other languages without introducing  foreign  libraries   Like boost  program options its API offers convenient direct access to options  i e  you can write code like this     if  options HELP           and     int verbosity   options VERBOSE  count      Unlike boost  program options however this is simply using an array indexed with a  user-provided  enum  This offers the convenience of an associative container without the weight   It s well documented and has a company-friendly license  MIT    TLMC  OP includes a nice formatter for usage messages that can do  line-wrapping and column alignment which is useful if you re localizing your program  because it ensures that the output will look good even in languages that have longer messages  It also saves you the nuisance of manually formatting your usage for 80 columns

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I d suggest using a library  There s the classic and venerable getopt and I m sure others

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I d suggest using a library  There s the classic and venerable getopt and I m sure others

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Instructional template for parsing command line arguments in C   C  programName -w -- fileOne txt fileTwo txt  BOOL argLine   FALSE  BOOL argWord   FALSE  BOOL argChar   FALSE  char   fileName1   NULL  char   fileName2   NULL   int main int argc  char   argv          int i      printf  Argument count  d n  argc       for  i   0  i  lt  argc  i              printf  Argument  s n  argv i            if  strcmp argv i   -l    0                argLine   TRUE              printf      argLine TRUE n                      else if  strcmp argv i   -w    0                argWord   TRUE              printf      argWord TRUE n                      else if  strcmp argv i   -c    0                argChar   TRUE              printf      argChar TRUE n                      else if  strcmp argv i   --    0                if  i 1  lt   argc                    fileName1   argv   i                   printf      fileName1  s n  fileName1                             if  i 1  lt   argc                    fileName2   argv   i                   printf      fileName2  s n  fileName2                                     return 0

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include  lt stdio h gt   int main int argc  char   argv        size t i      size t filename i   -1       for  i   0  i  lt  argc  i                  char const  option    argv i           if  option 0      -                         printf  I am a flagged option                switch  option 1                                 case  a                         someting                       break                  case  b                       break                  case  -                           --  -- the next argument will be a file                        filename i   i                      i   i   1                      break                  default                      printf  flag not recognised  s   option                       break                                  else                          printf  I am a positional argument                          At this point  if -- was specified  then filename i contains the index          into argv that contains the filename  If -- was not specified  then filename i will be -1            return 0

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If you don t want to use boost  I d recommend this little helper class

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Boost Program options  should do the trick

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And there s a Google library available   Really  command-line parsing is  solved    Just pick one

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There are these tools in the GNU C Library  which includes GetOpt   If you are using Qt and like the GetOpt interface  froglogic has published a nice interface here

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GNU GetOpt   A simple example using GetOpt      C C   Libraries   include  lt string gt   include  lt iostream gt   include  lt unistd h gt      Namespaces  using namespace std   int main int argc  char   argv        int opt      bool flagA   false      bool flagB   false          Shut GetOpt error messages down  return            opterr   0          Retrieve the options      while    opt   getopt argc  argv   ab       -1         for each option            switch   opt                 case  a                       flagA   true                  break              case  b                       flagB   true                  break              case          unknown option                        cerr  lt  lt   Unknown option      lt  lt  char optopt   lt  lt        lt  lt  endl                  break                          Debug      cout  lt  lt   flagA      lt  lt  flagA  lt  lt  endl      cout  lt  lt   flagB      lt  lt  flagB  lt  lt  endl       return 0      You can also use optarg if you have options that accept arguments

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Use getopt    or perhaps getopt long     int iflag   0  enum   WORD MODE  LINE MODE   op mode   WORD MODE      Default set int opt   while   opt   getopt argc  argv   ilw      -1        switch  opt            case  i           iflag   1          break      case  l           op mode   LINE MODE          break      case  w           op mode   WORD MODE          break      default          fprintf stderr   Usage   s  -ilw   file      n   argv 0            exit EXIT FAILURE               Process file names or stdin    if  optind  gt   argc      process stdin    standard input    op mode   else       int i      for  i   optind  i  lt  argc  i                  FILE  fp   fopen argv i    r            if  fp    0              fprintf stderr    s  failed to open  s   d  s  n                       argv 0   argv i   errno  strerror errno            else                       process fp  argv i   op mode               fclose fp                        Note that you need to determine which headers to include  I make it 4 that are required   and the way I wrote the op mode type means you have a problem in the function process   - you can t access the enumeration down there   It s best to move the enumeration outside the function  you might even make op mode a file-scope variable without external linkage  a fancy way of saying static  to avoid passing it to the function   This code does not handle - as a synonym for standard input  another exercise for the reader   Note that getopt   automatically takes care of -- to mark the end of options for you   I ve not run any version of the typing above past a compiler  there could be mistakes in it     For extra credit  write a  library  function   int filter int argc  char   argv  int idx  int   function  FILE  fp  const char  fn      which encapsulates the logic for processing file name options after the getopt   loop   It should handle - as standard input   Note that using this would indicate that op mode should be a static file scope variable   The filter   function takes argc  argv  optind and a pointer to the processing function   It should return 0  EXIT SUCCESS  if it was able to open all the files and all invocations of the function reported 0  otherwise 1  or EXIT FAILURE    Having such a function simplifies writing Unix-style  filter  programs that read files specified on the command line or standard input

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With C    the answer is usually in Boost     Boost Program Options

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argstream is quite similar to boost program option  it permits to bind variables to options  etc  However it does not handle options stored in a configuration file

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Your C C   program always has a main function  It looks like that       int main int argc  char  argv                        Here argc is a number of command line arguments  that have been passed to your program  and argv is an array of strings with these arguments  So command line is separated in-to arguments by the caller process  this is not a single line  like in windows    Now you need to sort them out    Command name is always the first argument  index 0   Options are just special arguments that specify how a program should work  By convention they start from - sign  Usually - for one letter options and -- for anything longer  So in your task  options  are all arguments  that start from - and are not the 0th  Arguments  Just all other arguments which are not program name or options

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I d recommend boost  program options if you can use the Boost lib   There s nothing specific in STL nor in the regular C   C runtime libs

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GNU GetOpt   A simple example using GetOpt      C C   Libraries   include  lt string gt   include  lt iostream gt   include  lt unistd h gt      Namespaces  using namespace std   int main int argc  char   argv        int opt      bool flagA   false      bool flagB   false          Shut GetOpt error messages down  return            opterr   0          Retrieve the options      while    opt   getopt argc  argv   ab       -1         for each option            switch   opt                 case  a                       flagA   true                  break              case  b                       flagB   true                  break              case          unknown option                        cerr  lt  lt   Unknown option      lt  lt  char optopt   lt  lt        lt  lt  endl                  break                          Debug      cout  lt  lt   flagA      lt  lt  flagA  lt  lt  endl      cout  lt  lt   flagB      lt  lt  flagB  lt  lt  endl       return 0      You can also use optarg if you have options that accept arguments

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If you just want to process command line options yourself  the easiest way is to put   vector lt string gt  args argv   1  argv   argc     at the top of your main     This copies all command-line arguments into a vector of std  strings   Then you can use    to compare strings easily  instead of endless strcmp   calls   For example   int main int argc  char   argv        vector lt string gt  args argv   1  argv   argc       string infname  outfname          Loop over command-line args         Actually I usually use an ordinary integer loop variable and compare        args i  instead of  i -- don t tell anyone         for  auto i   args begin    i    args end      i            if   i     -h      i     --help                 cout  lt  lt   Syntax  foomatic -i  lt infile gt  -o  lt outfile gt    lt  lt  endl              return 0            else if   i     -i                 infname      i            else if   i     -o                 outfname      i                       EDIT  I realised I was copying argv 0   the name of the program  into args -- fixed

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Boost program options

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Try CLPP library  It s simple and flexible library for command line parameters parsing  Header-only and cross-platform  Uses ISO C   and Boost C   libraries only  IMHO it is easier than Boost Program options   Library  http   sourceforge net projects clp-parser  26 October 2010 - new release 2 0rc  Many bugs fixed  full refactoring of the source code  documentation  examples and comments have been corrected

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Here s a rough one not relying on any libraries        Example        -wi   -iw   word case insensitive       -li   -il   line case insensitive       -- file    specify the first filename  you could just get the files       as positional arguments in the else statement instead        PS  don t mind the  define s  they re just pasting code  D             ifndef OPT H      define OPT H        specify option requires argument      define require         optarg   opt pointer   1          if   optarg      0                       if    optind    argc              goto opt err arg            else             optarg   argv optind                     opt pointer   opt null terminator         start processing argv      define opt       int   optind                   1        char  opt pointer              argv 1         char  optarg                   NULL        char  opt null terminator 2       0    0          if  0                  opt err arg            fprintf stderr  option  c requires argument  n   opt pointer             return 1          opt err opt            fprintf stderr  option  c is invalid  n   opt pointer             return 1                for    optind  lt  argc  opt pointer   argv   optind           if   opt pointer       -                       for      opt pointer              switch   opt pointer                       stop processing argv      define done             default                if   opt pointer      0                   goto opt err opt                else                 goto opt next                break                          opt next                  endif   opt h       include  lt stdio h gt       include  opt h      int     main  int argc  char   argv               define by character 0        define by word      1        define by line      2       int cmp   by character        int case insensitive   0        opt       case  h           puts   HELP             break        case  v           puts   fileCMP Version 1 0            break        case  i           case insensitive   1          break        case  w           cmp   by word          break        case  l           cmp   by line          break        case  -  required         printf  first filename   s n   optarg           break        done       else printf   Positional Argument  s n   argv optind          return 0

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Tooting my own horn if I may  I d also like to suggest taking a look at an option parsing library that I ve written  dropt    It s a C library  with a C   wrapper if desired   It s lightweight  It s extensible  custom argument types can be easily added and have equal footing with built-in argument types   It should be very portable  it s written in standard C  with no dependencies  other than the C standard library   It has a very unrestrictive license  zlib libpng     One feature that it offers that many others don t is the ability to override earlier options   For example  if you have a shell alias   alias bar  foo --flag1 --flag2 --flag3    and you want to use bar but with--flag1 disabled  it allows you to do   bar --flag1 0

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Following from my comment and from rbaleksandar s answer  the arguments passed to any program in C are string values  You are provided the argument count  argc  which gives you the argument indexes zero-based beginning with the name of the program currently being run  which is always argv 0    That leaves all arguments between 1 - argc as the user supplied arguments for your program  Each will be a string that is contained in the argument vector  which is a pointer to an array of strings you will seen written as char  argv    or equivalently as a function parameter char   argv  Each of the strings argv 1  to argv argc-1  are available to you  you simply need to test which argument is which   That will allow you to separate  and make them available as the command  cmd   the options  opt  and finally the argument  arg  to your cmd   Now it is worth noting  that the rules of your shell  bash  etc    apply to the arguments passed to your program  word-splitting  pathname and variable expansion apply before your code gets the arguments  So you must consider whether single or more commongly double-quoting will be required around any of your arguments to prevent the normal shell splitting that would otherwise apply  e g  ls -al my file txt would results in 4 user-supplied arguments to your code  while ls -al  my file txt  or ls -al my  file txt which would result in the 3 your were expecting   Putting all that together  your short bit of parsing could be done something like what follows   you are also free to do it however you like  using a switch instead of nested ifs  etc       include  lt stdio h gt   int main  int argc  char   argv         char  cmd   NULL       here  since you are using the arguments               opt   NULL       themselves  you can simply use a pointer              arg   NULL       or the argument itself without a copy               looping using the acutal argument index  amp  vector        for  int i   1  i  lt  argc  i              if   argv i      -             checking if the 1st char is -                if   cmd                   cmd is currently NULL  and                       cmd   argv i           no  -  it s going to be cmd                  else                       otherwise  cmd has value  so                     arg   argv i            the value will be opt                             else                   here the value has a leading  -   so                 opt   argv i       it will be the option               printf    n cmd    s n opt    s n arg    s n n               cmd  opt  arg        return 0      Example Use Output  If you run the code  you will find it provides separation for the arguments and provides separate pointers to facilitate their use       bin parse cmd ls -la   cs3000   cmd   ls  opt   -la  arg     cs3000    it is important to note  that if you were tasked with building a command string where you would need to copy multiple value to say opt or arg  then  you could no longer simply use a pointer and would need to create storage  either though a simple declaring of arrays instead of pointer to begin with  or you could dynamically allocate storage as required with  e g  malloc  calloc and or realloc  Then you would have storage available to copy and concatenate values within    If this was your challenge  then between all the answer here  you should have a handle of how to approach your problem  If you must go further and actually have your program execute the cmd with the opt and the arg  then you will want to look at fork to spawn a semi-separate process within which you run would execute your cmd opt and arg with something similar to execv or execvp  Good luck  and post a comment if you have further questions

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I ve found Gengetopt to be quite useful - you specify the options you want with a simple configuration file  and it generates a  c  h pair that you simply include and link with your application  The generated code makes use of getopt long  appears to handle most common sorts of command line parameters  and it can save a lot of time   A gengetopt input file might look something like this   version  0 1  package  myApp  purpose  Does something useful      Options option  filename  f  Input filename  string required option  verbose  v  Increase program verbosity  flag off option  id  i  Data ID  int required option  value  r  Data value  multiple 1-  int optional    Generating the code is easy and spits out cmdline h and cmdline c     gengetopt --input myApp cmdline --include-getopt   The generated code is easily integrated    include  lt stdio h gt   include  cmdline h   int main int argc  char    argv      struct gengetopt args info ai    if  cmdline parser argc  argv   amp ai     0        exit 1         printf  ai filename arg   s n   ai filename arg     printf  ai verbose flag   d n   ai verbose flag     printf  ai id arg   d n   ai id arg     int i    for  i   0  i  lt  ai value given    i        printf  ai value arg  d    d n   i  ai value arg i            If you need to do any extra checking  such as ensuring flags are mutually exclusive   you can do this fairly easily with the data stored in the gengetopt args info struct

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You can use GNU GetOpt  LGPL  or one of the various C   ports  such as getoptpp  GPL    A simple example using GetOpt of what you want  prog  -ab  input  is the following      C Libraries   include  lt string gt   include  lt iostream gt   include  lt unistd h gt      Namespaces  using namespace std   int main int argc  char   argv        int opt      string input           bool flagA   false      bool flagB   false          Retrieve the  non-option  argument      if    argc  lt   1      argv argc-1     NULL      argv argc-1  0      -           there is NO input            cerr  lt  lt   No argument provided    lt  lt  endl            return 1            else       there is an input            input   argv argc-1                 Debug      cout  lt  lt   input      lt  lt  input  lt  lt  endl          Shut GetOpt error messages down  return            opterr   0          Retrieve the options      while    opt   getopt argc  argv   ab       -1         for each option            switch   opt                 case  a                       flagA   true                  break              case  b                       flagB   true                  break              case          unknown option                        cerr  lt  lt   Unknown option      lt  lt  char optopt   lt  lt        lt  lt  endl                  break                          Debug      cout  lt  lt   flagA      lt  lt  flagA  lt  lt  endl      cout  lt  lt   flagB      lt  lt  flagB  lt  lt  endl       return 0

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There are these tools in the GNU C Library  which includes GetOpt   If you are using Qt and like the GetOpt interface  froglogic has published a nice interface here

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You probably want to use an external library for that   There are many to chose from   Boost has a very feature-rich  as usual  library Boost Program Options   My personal favorite for the last few years has been TCLAP -- purely templated  hence no library or linking  automated  --help  generation and other goodies  See the simplest example from the docs

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I find it easier to use ezOptionParser  It s also a single header file  does not depend on anything but STL  works for Windows and Linux  very likely other platforms too   has no learning curve thanks to the examples  has features other libraries don t  like file import export with comments  arbitrary option names with delimiters  auto usage formatting  etc   and is LGPL licensed

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This is my favourite way of doing the command line  especially  but definitely not only when efficiency is an issue  It might seem overkill  but I think there are few disadvantages to this overkill   Use gperf for efficient C C   command line processing  Disadvantages    You have to run a separate tool first to generate the code for a hash table in C C   No support for specific command line interfaces  For example the posix shorthand system  -xyz  declaring multiple options with one dash would be hard to implement    Advantages    Your command line options are stored separately from your C   code  in a separate  configuration file  which doesn t need to be read at runtime  only at compile time   All you have in your code is exactly one switch  switching on enum values  to figure out which option you have Efficiency is O n  where n is the number of options on the command line and the number of possible options is irrelevant  The slowest part is possibly the implementation of the switch  sometimes compilers tend to implement them as if else blocks  reducing their efficiency  albeit this is unlikely if you choose contiguous values  see  this article on switch efficiency   The memory allocated to store the keywords is precisely large enough for the keyword set and no larger   Also works in C   Using an IDE like eclipse you can probably automate the process of running gperf  so the only thing you would have to do is add an option to the config file and to your switch statement and press build      I used a batch file to run gperf and do some cleanup and add include guards with sed  on the gperf generated  hpp file      So  extremely concise and clean code within your software and one auto-generated hash table file that you don t really need to change manually  I doubt if boost  program options actually would beat that even without efficiency as a priority

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TCLAP is a really nice lightweight design and easy to use  http   tclap sourceforge net

[c] Parsing command-line arguments in C

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