Thread: expected ‘const char *’

Hello everyone I am still new to c but going throught a book called Learn c on the mac but I am using Ubuntu. I wrote a easy little program in witch it will ping all ip addresses from 192.168.6.1 to 192.168.6.254 once and print the responce out. I am getting "/usr/include/stdio.h:870:14: note: expected ‘const char *’ but argument is of type ‘int’" but I can't figure out why becuase I get the error on this line.

Code:

            fp = popen(ping, 'r');

but they are declared like this

Code:

 
        char ping[30];
        FILE *fp;

here is the whole thing.

Code:

#include <stdio.h>
#include <stdlib.h>
    main(){
        int count = 0;
        char ping[30];
        FILE *fp;
        char op[200];
        while( count = 1, count <= 254, count++) 
        {
            sprintf(ping, "ping -c 1 192.168.6.%d", count);
            fp = popen(ping, 'r');

              while (fgets(op, sizeof(op)-1, fp) != NULL) 
                  {
                        printf("%s", op);
                  }
        } 





        return 0;
        }

I have been seraching the internet but I am still unable to figure out why I am getting this, anyone have an idea?
Thank you to anyone who replies.

FILE *popen(const char *command, const char *type);

The type argument is a pointer to a null-terminated string which must contain either the letter 'r' for reading or the letter 'w' for writing.

(source: popen(3): pipe stream to/from process - Linux man page)

Note you're using a single character ('r') as the second argument. Make it a string by using double quotes instead ("r").

Thanks for your help, that did the trick I'm not sure I understand why but I look in to the man pages.
Thanks Again.

Originally Posted by willane1965

Thanks for your help, that did the trick I'm not sure I understand why but I look in to the man pages.

'r' represents a single character.

"r" represents a c-string (which is a series of zero or more characters terminated with a null character, '\0').

More reading: C Strings - Cprogramming.com