Question 26764 in CentOS Question posted in
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Getopt not recognizing command line arguments (C program) – CentOS

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 intentn ");
 printf("This program forks off a single child process to do a taskn ");
 printf("The main process will wait for it to complete and then don");
 printf("some additional workn");
}

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

2

Answers


  1. 0
    1. You are missing the two header files:
    #include <stdio.h>
#include <unistd.h>

    and you are missing a return statement:

    return 0;
    1. 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.

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

    2. 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 intentn"
        "This program forks off a single child process to do a taskn"
        "The main process will wait for it to complete and then don"
        "some additional workn"
    );
}

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;
}
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  2. 0

    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.

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