Creating a simple configuration file and parser in C

Question

I am trying to create a simple configuration file that looks like this  url   http   mysite com file   main exe true   0   when the program runs  I would like it to load the configuration settings into the programs variables listed below   string url  file  bool true false    I have done some research and this link seemed to help  nucleon s post  but I can t seem to get it to work and it is too complicated to understand on my part  Is there a simple way of doing this  I can load the file using ifstream but that is as far as I can get on my own  Thanks

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A naive approach could look like this    include  lt map gt   include  lt sstream gt   include  lt stdexcept gt   include  lt string gt   std  map lt std  string  std  string gt  options     global   void parse std  istream  amp  cfgfile        for  std  string line  std  getline cfgfile  line                   std  istringstream iss line           std  string id  eq  val           bool error   false           if    iss  gt  gt  id                         error   true                    else if  id 0                                continue                    else if    iss  gt  gt  eq  gt  gt  val  gt  gt  std  ws     eq           iss get      EOF                        error   true                     if  error                           do something appropriate  throw  skip  warn  etc                    else                       options id    val                      Now you can access each option value from the global options map anywhere in your program  If you want castability  you could make the mapped type a boost  variant

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libconfig is very easy  and what s better  it uses a pseudo json notation for better readability   Easy to install on Ubuntu  sudo apt-get install libconfig  8-dev  and link  -lconfig

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Why not trying something simple and human-readable  like JSON  or XML      There are many pre-made open-source implementations of JSON  or XML  for C   - I would use one of them   And if you want something more  binary  - try BJSON or BSON

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As others have pointed out  it will probably be less work to make use of an existing configuration-file parser library rather than re-invent the wheel   For example  if you decide to use the Config4Cpp library  which I maintain   then your configuration file syntax will be slightly different  put double quotes around values and terminate assignment statements with a semicolon  as shown in the example below     File  someFile cfg url    http   mysite com   file    main exe   true false    true     The following program parses the above configuration file  copies the desired values into variables and prints them    include  lt config4cpp Configuration h gt   include  lt iostream gt  using namespace config4cpp  using namespace std   int main int argc  char    argv        Configuration    cfg   Configuration  create        const char       scope           const char       configFile    someFile cfg       const char       url      const char       file      bool             true false       try           cfg- gt parse configFile           url          cfg- gt lookupString scope   url            file         cfg- gt lookupString scope   file            true false   cfg- gt lookupBoolean scope   true false          catch const ConfigurationException  amp  ex            cerr  lt  lt  ex c str    lt  lt  endl          cfg- gt destroy            return 1            cout  lt  lt   url    lt  lt  url  lt  lt     file    lt  lt  file           lt  lt     true false    lt  lt  true false           lt  lt  endl      cfg- gt destroy        return 0      The Config4Cpp website provides comprehensive documentation  but reading just Chapters 2 and 3 of the  Getting Started Guide  should be more than sufficient for your needs

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So I merged some of the above solutions into my own  which for me made more sense  became more intuitive and a bit less error prone  I use a public stp  map to keep track of the possible config ids  and a struct to keep track of the possible values  Her it goes   struct      std  string PlaybackAssisted    assisted       std  string Playback    playback       std  string Recording    record       std  string Normal    normal     mode def   std  map lt std  string  std  string gt  settings           mode   mode def Normal         output log path     home root output data log          input log path     home root input data log        void read config const std  string  amp  settings path   std  ifstream settings file settings path   std  string line   if  settings file fail         LOG WARN  Config file does not exist  Default options set to         for  auto it   settings begin    it    settings end    it             LOG INFO   s  s   it- gt first c str    it- gt second c str              while  std  getline settings file  line        std  istringstream iss line       std  string id  eq  val       if  std  getline iss  id                 if  std  getline iss  val                if  settings find id     settings end                     if  val empty                         LOG INFO  Config    s   is empty  Keeping default    s     id c str    settings id  c str                                       else                      settings id    val                      LOG INFO  Config    s   read as    s     id c str    settings id  c str                                                 else    Not present in map                 LOG ERROR  Setting    s   not defined  ignoring it   id c str                     continue                                  else                 Comment line  skiping it             continue                      else            Empty line  skipping it         continue

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I ve searched config parsing libraries for my project recently and found these libraries    http   www hyperrealm com libconfig  - small but powerfull and easy-to-use library  examples of using are in the source package and here  http   pocoproject org docs Poco Util PropertyFileConfiguration html - a part of pocoproject  You can use abstraction in your code and behind that use various supported implementations  ini files  Xml configs  even environment variables

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I was looking for something that worked like the python module ConfigParser and found this  https   github com jtilly inih     This is a header only C   version of inih       inih  INI Not Invented Here  is a simple  INI file parser written in   C  It s only a couple of pages of code  and it was designed to be   small and simple  so it s good for embedded systems  It s also more or   less compatible with Python s ConfigParser style of  INI files    including RFC 822-style multi-line syntax and name  value entries

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I was searching for a similar simple C   config file parser and this tutorial website provided me with a basic yet working solution  Its quick and dirty soultion to get the job done   myConfig txt  gamma 2 8 mode     1 path   D  Photoshop Projects Workspace Images    The following program reads the previous configuration file    include  lt iostream gt   include  lt fstream gt   include  lt algorithm gt   include  lt string gt   int main         double gamma   0      int mode   0      std  string path          std  ifstream is RAII  i e  no need to call close     std  ifstream cFile  myConfig txt        if  cFile is open                  std  string line          while  getline cFile  line                          line erase std  remove if line begin    line end    isspace  line end                 if  line 0            line empty    continue               auto delimiterPos   line find                   auto name   line substr 0  delimiterPos               auto value   line substr delimiterPos   1                  Custom coding             if  name     gamma   gamma   std  stod value               else if  name     mode   mode   std  stoi value               else if  name     path   path   value                      else                std  cerr  lt  lt   Couldn t open config file for reading  n              std  cout  lt  lt    nGamma    lt  lt  gamma      std  cout  lt  lt    nMode    lt  lt  mode      std  cout  lt  lt    nPath    lt  lt  path      std  getchar

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SimpleConfigFile is a library that does exactly what you require and it is very simple to use     File file cfg url   http   example com file   main exe true   0    The following program reads the previous configuration file    include lt iostream gt   include lt string gt   include lt vector gt   include  config file h   int main void           Variables that we want to read from the config file     std  string url  file      bool true false          Names for the variables in the config file  They can be different from the actual variable names      std  vector lt std  string gt  ln     url   file   true            Open the config file for reading     std  ifstream f in  file cfg         CFG  ReadFile f in  ln  url  file  true false       f in close         std  cout  lt  lt   url     lt  lt  url  lt  lt  std  endl      std  cout  lt  lt   file     lt  lt  file  lt  lt  std  endl      std  cout  lt  lt   true     lt  lt  true false  lt  lt  std  endl       return 0      The function CFG  ReadFile uses variadic templates  This way  you can pass the variables you want to read and the corresponding type is used for reading the data in the appropriate way

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How about formatting your configuration as JSON  and using a library like jsoncpp    e g     url    http   mysite dot com    file    main exe    true   0    You can then read it into named variables  or even store it all in a std  map  etc  The latter means you can add options without having to change and recompile your configuration parser

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In general  it s easiest to parse such typical config files in two stages  first read the lines  and then parse those one by one  In C    lines can be read from a stream using std  getline    While by default it will read up to the next   n   which it will consume  but not return   you can pass it some other delimiter  too  which makes it a good candidate for reading up-to-some-char  like   in your example    For simplicity  the following presumes that the   are not surrounded by whitespace  If you want to allow whitespaces at these positions  you will have to strategically place is  gt  gt  std  ws before reading the value and remove trailing whitespaces from the keys  However  IMO the little added flexibility in the syntax is not worth the hassle for a config file reader    const char config      url http   example com n                         file main exe n                         true 0    std  istringstream is file config    std  string line  while  std  getline is file  line        std  istringstream is line line     std  string key    if  std  getline is line  key                 std  string value      if  std  getline is line  value           store line key  value            Adding error handling is left as an exercise to the reader

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I would like to recommend a single header C   11 YAML parser mini-yaml  A quick-start example taken from the above repository  file txt key  foo bar list    - hello world   - integer  123     boolean  true   cpp Yaml  Node root  Yaml  Parse root   quot file txt quot        Print all scalars  std  cout  lt  lt  root  quot key quot   As lt std  string gt     lt  lt  std  endl  std  cout  lt  lt  root  quot list quot   0  As lt std  string gt     lt  lt  std  endl  std  cout  lt  lt  root  quot list quot   1   quot integer quot   As lt int gt     lt  lt  std  endl  std  cout  lt  lt  root  quot list quot   1   quot boolean quot   As lt bool gt     lt  lt  std  endl      Iterate second sequence item  Node  amp  item   root 1   for auto it   item Begin    it    item End    it          std  cout  lt  lt    it  first  lt  lt   quot    quot   lt  lt    it  second As lt string gt     lt  lt  std  endl     Output foo bar hello world 123 1 integer  123 boolean  true

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Here is a simple work around for white space between the     sign and the data  in the config file  Assign to the istringstream from the location after the     sign and when reading from it  any leading white space is ignored   Note  while using an istringstream in a loop  make sure you call clear   before assigning a new string to it     config txt   Input name   image1 png   Num  of rows   100   Num  of cols   150  std  string ipName  int nR  nC   std  ifstream fin  config txt    std  string line  std  istringstream sin   while  std  getline fin  line      sin str line substr line find      1     if  line find  Input name      std  string  npos      std  cout lt  lt  Input name   lt  lt sin str   lt  lt std  endl    sin  gt  gt  ipName      else if  line find  Num  of rows      std  string  npos      sin  gt  gt  nR      else if  line find  Num  of cols      std  string  npos      sin  gt  gt  nC      sin clear

[c++] Creating a simple configuration file and parser in C++

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