I am creating a C program in CentOS linux, and I cannot get my getopt to recognize arguments from the command line. I am relatively new to linux and C.

The error I get is 'command not found' I compiled the file using gcc and executing with ./testFile compile command was: gcc mathwait.c -o testFile and then ./testFile

thanks for your help!

void help()
{
 printf("The options for this program are:\n ");
 printf("-h - walkthrough of options and program intent\n ");
 printf("This program forks off a single child process to do a task\n ");
 printf("The main process will wait for it to complete and then do\n");
 printf("some additional work\n");
}

int main(int argc, char **argv)
{
 int option;
 while((option = getopt(argc, argv, "h")) != -1)
{
  switch(option)
 {
  case 'h':
   help();
  break;
  default:
   help();
  break;
 }
}
}

CodePudding user response：

1. You are missing the two header files:

#include <stdio.h>
#include <unistd.h>

and you are missing a return statement:

return 0;

2. Per getopt(3) man page:

If there are no more option characters, getopt() returns -1

This means if you don't supply any arguments getopt() will return -1 and you while() loop is not being executed and your program will exit. If you call your program with -h the first case will be executed, otherwise (meaning any other arguments) the default case will be executed.

3. I assume this is test code, otherwise there is no point of having a switch when you do the same thing in all cases.

4. Formatting matters for readability:

#include <stdio.h>
#include <unistd.h>

void help() {
    printf(
        "The options for this program are:\n"
        "-h - walkthrough of options and program intent\n"
        "This program forks off a single child process to do a task\n"
        "The main process will wait for it to complete and then do\n"
        "some additional work\n"
    );
}

int main(int argc, char **argv) {
    int option;
    while((option = getopt(argc, argv, "h")) != -1) {
        switch(option) {
            case 'h':
                help();
                break;
            default:
                help();
                break;
        }
    }
    return 0;
}

CodePudding user response：

You say:

compile command was: gcc mathwait.c -o testFile and then ./testFile

If you run ./testFile, you are not providing any arguments. Run:

./testFile -h

Now you provide an option for getopt() to process. If you ran ./testFile -x, you'd get a message about an unrecognized option 'x' and then the information from the help() function.