Parsing command line arguments in C

Question

I have a program that needs to use variables that should be set when the program is called from the command line. I want the user to be able to specify options -r, -o, -s, and -p along with some integer. I've never dealt with command line arguments before but after doing some research I came up with the following:

int main(int argc, char *argv[]){
    for(k = 1; k < argc; k = k+2){
        if(std::string(argv[k]) == "-r"){
           n = atoi(std::string(argv[k+1]));
        }else if(std::string(argv[k]) == "-o"){
           o = atoi(std::string(argv[k+1]));
        }else if(std::string(argv[k]) == "-s"){
           p = atoi(std::string(argv[k+1]));
        }else{
          n = 1; o = 2; p = 3;
        }
    }
}

My idea is that the user would call the program like so:

$ ./my_program -r 1000 -o 10000000 -s 1

in order to set the variables in my program accordingly. However, when I try to compile this with my makefile, I get an error:

    error: std undeclared (first use in this function)
        if(std::string(argv[k]) == "-r"){
           ^

There are many more but I can't type them all. I'm sure if I figure out this error I can figure out the others. Why doesn't C like me?

EDIT:

As a quick note, I did include , but this does not fix any of the errors and the output when calling make is still the same.

#include <string> (you tagged C, but the code you posted is C++) — TypeIA
– TypeIA, Commented Mar 9, 2014 at 6:54
Then you should have said so, and included the "fatal error," in your question. We can't help you solve problems without all the information. — TypeIA
– TypeIA, Commented Mar 9, 2014 at 6:58
std::string does not exist in C; to compare strings you would use the strcmp() function. You may want to consider using a library that already has commandline arguments worked out, such as GNU getopt. — M.M
– M.M, Commented Mar 9, 2014 at 7:04
Possible duplicate of Parsing command-line arguments? There are also many other questions that this could be a duplicate of. — Jonathan Leffler
– Jonathan Leffler, Commented Mar 9, 2014 at 7:18

brokenfoot · Accepted Answer · 2014-03-09 07:03:47Z

2

You should use getopt() here. The getopt() and getopt_long functions automate some of the chore involved in parsing typical unix command line options. It will save you all the effort.

http://www.ibm.com/developerworks/aix/library/au-unix-getopt.html

answered Mar 9, 2014 at 7:03

brokenfoot

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