C - reading command line parameters

Question

I have made little program for computing pi  p  as an integral  Now I am facing a question how to extend it to compute an integral  which will be given as an extra parameter when starting an application  How do I deal with such a parameter in a program

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There s also a C standard built-in library to get command line arguments  getopt  You can check it on Wikipedia or in Argument-parsing helpers for C Unix

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When you write your main function  you typically see one of two definitions   int main void  int main int argc  char   argv   The second form will allow you to access the command line arguments passed to the program  and the number of arguments specified  arguments are separated by spaces   The arguments to main are   int argc - the number of arguments passed into your program when it was run  It is at least 1  char   argv - this is a pointer-to-char    It can alternatively be this  char  argv    which means  array of char     This is an array of C-style-string pointers    Basic Example For example  you could do this to print out the arguments passed to your C program   include  lt stdio h gt   int main int argc  char   argv        for  int i   0  i  lt  argc    i                printf  quot argv  d    s n quot   i  argv i             I m using GCC 4 5 to compile a file I called args c  It ll compile and build a default a out executable   birryree lilun c code   gcc -std c99 args c  Now run it     birryree lilun c code     a out hello there argv 0     a out argv 1   hello argv 2   there  So you can see that in argv  argv 0  is the name of the program you ran  this is not standards-defined behavior  but is common  Your arguments start at argv 1  and beyond  So basically  if you wanted a single parameter  you could say      myprogram integral  A Simple Case for You And you could check if argv 1  was integral  maybe like strcmp  quot integral quot   argv 1      0  So in your code     include  lt stdio h gt   include  lt string h gt   int main int argc  char   argv        if  argc  lt  2     no arguments were passed                  do something            if  strcmp  quot integral quot   argv 1      0                runIntegral         or something           else                  do something else            Better command line parsing Of course  this was all very rudimentary  and as your program gets more complex  you ll likely want more advanced command line handling  For that  you could use a library like GNU getopt

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include  lt stdio h gt   include  lt stdlib h gt   int main int argc  char   argv      int i  parameter   0    if  argc  gt   2           there is 1 parameter  or more  in the command line used           argv 0  may point to the program name           argv 1  points to the 1st parameter           argv argc  is NULL        parameter   atoi argv 1       better to use strtol        if  parameter  gt  0          for  i   0  i  lt  parameter  i    printf   d    i         else         fprintf stderr   Please use a positive integer  n                return 0

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Parsing command line arguments in a primitive way as explained in the above answers is reasonable as long as the number of parameters that you need to deal with is not too much   I strongly suggest you to use an industrial strength library for handling the command line arguments   This will make your code more professional   Such a library for C   is available in the following website  I have used this library in many of my projects  hence I can confidently say that this one of the easiest yet useful library for command line argument parsing  Besides  since it is just a template library  it is easier to import into your project  http   tclap sourceforge net   A similar library is available for C as well  http   argtable sourceforge net

[c] C - reading command line parameters

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