Pass arguments into C program from command line

Question

So I m in Linux and I want to have a program accept arguments when you execute it from the command line   For example      myprogram 42 -b -s  So then the program would store that number 42 as an int and execute certain parts of code depending on what arguments it gets like -b or -s

User · Accepted Answer

You could use getopt     include  lt ctype h gt    include  lt stdio h gt    include  lt stdlib h gt    include  lt unistd h gt    int  main  int argc  char   argv        int bflag   0     int sflag   0     int index     int c      opterr   0      while   c   getopt  argc  argv   bs       -1       switch  c                  case  b            bflag   1           break         case  s            sflag   1           break         case               if  isprint  optopt              fprintf  stderr   Unknown option  - c   n   optopt            else            fprintf  stderr                       Unknown option character    x x   n                       optopt            return 1         default           abort                  printf   bflag    d  sflag    d n   bflag  sflag       for  index   optind  index  lt  argc  index         printf   Non-option argument  s n   argv index       return 0

User · Answer

Take a look at the getopt library  it s pretty much the gold standard for this sort of thing

User · Answer

Other have hit this one on the head    the standard arguments to main int argc  char   argv  give you direct access to the command line  after it has been mangled and tokenized by the shell  there are very standard facility to parse the command line  getopt   and getopt long     but as you ve seen the code to use them is a bit wordy  and quite idomatic  I generally push it out of view with something like   typedef struct options struct      int some flag     int other flage     char  use file    opt t     Parses the command line and fills the options structure      returns non-zero on error    int parse options opt t  opts  int argc  char   argv     Then first thing in main   int main int argc  char   argv      opt t opts     if  parse options  amp opts argc argv                               Or you could use one of the solutions suggested in Argument-parsing helpers for C UNIX

User · Answer

Other have hit this one on the head    the standard arguments to main int argc  char   argv  give you direct access to the command line  after it has been mangled and tokenized by the shell  there are very standard facility to parse the command line  getopt   and getopt long     but as you ve seen the code to use them is a bit wordy  and quite idomatic  I generally push it out of view with something like   typedef struct options struct      int some flag     int other flage     char  use file    opt t     Parses the command line and fills the options structure      returns non-zero on error    int parse options opt t  opts  int argc  char   argv     Then first thing in main   int main int argc  char   argv      opt t opts     if  parse options  amp opts argc argv                               Or you could use one of the solutions suggested in Argument-parsing helpers for C UNIX

User · Answer

In C  this is done using arguments passed to your main   function   int main int argc  char  argv          int i   0      for  i   0  i  lt  argc  i              printf  argv  d     s n   i  argv i              return 0      More information can be found online such as this Arguments to main article

User · Answer

Instead of getopt    you may also consider using argp parse    an alternative interface to the same library     From libc manual      getopt is more standard  the   short-option only version of it is a   part of the POSIX standard   but using   argp parse is often easier  both for   very simple and very complex option   structures  because it does more of   the dirty work for you    But I was always happy with the standard getopt   N B  GNU getopt with getopt long is GNU LGPL

User · Answer

Consider using getopt long    It allows both short and long options in any combination    include  lt stdio h gt   include  lt stdlib h gt   include  lt getopt h gt      Flag set by  --verbose      static int verbose flag   int main  int argc  char  argv        while  1              static struct option long options                    This option set a flag             verbose   no argument         amp verbose flag  1            These options don t set a flag           We distinguish them by their indices             blip      no argument        0   b            slip      no argument        0   s           0          0                  0   0                  getopt long stores the option index here           int option index   0         int c   getopt long  argc  argv   bs                  long options   amp option index             Detect the end of the options           if  c    -1      break         switch  c            case 0           If this option set a flag  do nothing else now           if  long options option index  flag    0          break        printf   option  s   long options option index  name         if  optarg          printf    with arg  s   optarg         printf    n          break      case  b         puts   option -b n          break      case  s         puts   option -s n          break      case               getopt long already printed an error message           break       default        abort                    if  verbose flag      puts   verbose flag is set          Print any remaining command line arguments  not options        if  optind  lt  argc              printf   non-option ARGV-elements            while  optind  lt  argc      printf    s    argv optind            putchar    n             return 0      Related    Which command line commands style do you prefer  What is the general syntax of a Unix shell command

User · Answer

Consider using getopt long    It allows both short and long options in any combination    include  lt stdio h gt   include  lt stdlib h gt   include  lt getopt h gt      Flag set by  --verbose      static int verbose flag   int main  int argc  char  argv        while  1              static struct option long options                    This option set a flag             verbose   no argument         amp verbose flag  1            These options don t set a flag           We distinguish them by their indices             blip      no argument        0   b            slip      no argument        0   s           0          0                  0   0                  getopt long stores the option index here           int option index   0         int c   getopt long  argc  argv   bs                  long options   amp option index             Detect the end of the options           if  c    -1      break         switch  c            case 0           If this option set a flag  do nothing else now           if  long options option index  flag    0          break        printf   option  s   long options option index  name         if  optarg          printf    with arg  s   optarg         printf    n          break      case  b         puts   option -b n          break      case  s         puts   option -s n          break      case               getopt long already printed an error message           break       default        abort                    if  verbose flag      puts   verbose flag is set          Print any remaining command line arguments  not options        if  optind  lt  argc              printf   non-option ARGV-elements            while  optind  lt  argc      printf    s    argv optind            putchar    n             return 0      Related    Which command line commands style do you prefer  What is the general syntax of a Unix shell command

User · Answer

Take a look at the getopt library  it s pretty much the gold standard for this sort of thing

User · Answer

In C  this is done using arguments passed to your main   function   int main int argc  char  argv          int i   0      for  i   0  i  lt  argc  i              printf  argv  d     s n   i  argv i              return 0      More information can be found online such as this Arguments to main article

User · Answer

In C  this is done using arguments passed to your main   function   int main int argc  char  argv          int i   0      for  i   0  i  lt  argc  i              printf  argv  d     s n   i  argv i              return 0      More information can be found online such as this Arguments to main article

User · Answer

Instead of getopt    you may also consider using argp parse    an alternative interface to the same library     From libc manual      getopt is more standard  the   short-option only version of it is a   part of the POSIX standard   but using   argp parse is often easier  both for   very simple and very complex option   structures  because it does more of   the dirty work for you    But I was always happy with the standard getopt   N B  GNU getopt with getopt long is GNU LGPL

User · Answer

Other have hit this one on the head    the standard arguments to main int argc  char   argv  give you direct access to the command line  after it has been mangled and tokenized by the shell  there are very standard facility to parse the command line  getopt   and getopt long     but as you ve seen the code to use them is a bit wordy  and quite idomatic  I generally push it out of view with something like   typedef struct options struct      int some flag     int other flage     char  use file    opt t     Parses the command line and fills the options structure      returns non-zero on error    int parse options opt t  opts  int argc  char   argv     Then first thing in main   int main int argc  char   argv      opt t opts     if  parse options  amp opts argc argv                               Or you could use one of the solutions suggested in Argument-parsing helpers for C UNIX

User · Answer

Consider using getopt long    It allows both short and long options in any combination    include  lt stdio h gt   include  lt stdlib h gt   include  lt getopt h gt      Flag set by  --verbose      static int verbose flag   int main  int argc  char  argv        while  1              static struct option long options                    This option set a flag             verbose   no argument         amp verbose flag  1            These options don t set a flag           We distinguish them by their indices             blip      no argument        0   b            slip      no argument        0   s           0          0                  0   0                  getopt long stores the option index here           int option index   0         int c   getopt long  argc  argv   bs                  long options   amp option index             Detect the end of the options           if  c    -1      break         switch  c            case 0           If this option set a flag  do nothing else now           if  long options option index  flag    0          break        printf   option  s   long options option index  name         if  optarg          printf    with arg  s   optarg         printf    n          break      case  b         puts   option -b n          break      case  s         puts   option -s n          break      case               getopt long already printed an error message           break       default        abort                    if  verbose flag      puts   verbose flag is set          Print any remaining command line arguments  not options        if  optind  lt  argc              printf   non-option ARGV-elements            while  optind  lt  argc      printf    s    argv optind            putchar    n             return 0      Related    Which command line commands style do you prefer  What is the general syntax of a Unix shell command

User · Answer

Other have hit this one on the head    the standard arguments to main int argc  char   argv  give you direct access to the command line  after it has been mangled and tokenized by the shell  there are very standard facility to parse the command line  getopt   and getopt long     but as you ve seen the code to use them is a bit wordy  and quite idomatic  I generally push it out of view with something like   typedef struct options struct      int some flag     int other flage     char  use file    opt t     Parses the command line and fills the options structure      returns non-zero on error    int parse options opt t  opts  int argc  char   argv     Then first thing in main   int main int argc  char   argv      opt t opts     if  parse options  amp opts argc argv                               Or you could use one of the solutions suggested in Argument-parsing helpers for C UNIX

User · Answer

In C  this is done using arguments passed to your main   function   int main int argc  char  argv          int i   0      for  i   0  i  lt  argc  i              printf  argv  d     s n   i  argv i              return 0      More information can be found online such as this Arguments to main article

User · Answer

Take a look at the getopt library  it s pretty much the gold standard for this sort of thing

User · Answer

Consider using getopt long    It allows both short and long options in any combination    include  lt stdio h gt   include  lt stdlib h gt   include  lt getopt h gt      Flag set by  --verbose      static int verbose flag   int main  int argc  char  argv        while  1              static struct option long options                    This option set a flag             verbose   no argument         amp verbose flag  1            These options don t set a flag           We distinguish them by their indices             blip      no argument        0   b            slip      no argument        0   s           0          0                  0   0                  getopt long stores the option index here           int option index   0         int c   getopt long  argc  argv   bs                  long options   amp option index             Detect the end of the options           if  c    -1      break         switch  c            case 0           If this option set a flag  do nothing else now           if  long options option index  flag    0          break        printf   option  s   long options option index  name         if  optarg          printf    with arg  s   optarg         printf    n          break      case  b         puts   option -b n          break      case  s         puts   option -s n          break      case               getopt long already printed an error message           break       default        abort                    if  verbose flag      puts   verbose flag is set          Print any remaining command line arguments  not options        if  optind  lt  argc              printf   non-option ARGV-elements            while  optind  lt  argc      printf    s    argv optind            putchar    n             return 0      Related    Which command line commands style do you prefer  What is the general syntax of a Unix shell command

User · Answer

Instead of getopt    you may also consider using argp parse    an alternative interface to the same library     From libc manual      getopt is more standard  the   short-option only version of it is a   part of the POSIX standard   but using   argp parse is often easier  both for   very simple and very complex option   structures  because it does more of   the dirty work for you    But I was always happy with the standard getopt   N B  GNU getopt with getopt long is GNU LGPL

User · Answer

Instead of getopt    you may also consider using argp parse    an alternative interface to the same library     From libc manual      getopt is more standard  the   short-option only version of it is a   part of the POSIX standard   but using   argp parse is often easier  both for   very simple and very complex option   structures  because it does more of   the dirty work for you    But I was always happy with the standard getopt   N B  GNU getopt with getopt long is GNU LGPL

User · Answer

Take a look at the getopt library  it s pretty much the gold standard for this sort of thing

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