Thread: Help with GCC arguments

Originally Posted by Salem

Well gmp and readline are separate libraries you (or your system administrator) need to install.

> -lgmp -lreadline
It's just like the -lm argument. It instructs the linker (that is /usr/bin/ld) to search those libraries for definitions which your program might need. I guess your test program doesn't actually need any of these things.

The 2>&1 notation is a shell redirection operator, which in this instance redirects the sderr stream onto the stdout stream.
I/O Redirection

Thanks,

What is the name of the libraries to install?

Originally Posted by NunoF

What is the name of the libraries to install?

You don't need to install any of those libraries since your program is not using them.

Your compile command can simply be:
gcc -o demo main.c

Then run it:
./demo

All those -l flags and the -pthread flag aren't needed for your program. The -l flags tell the linker the names of non-standard libraries being used (and on some systems the math library). But your program doesn't need any of them.

The reason the compiler is complaining is that you don't have some of those libraries on that machine, which isn't a problem since you aren't using them and if you ever need them they can be easily installed.

A better compile command, with a more recent C standard and higher warning level, is:
gcc -std=c99 -Wall -o demo main.c

Many thanks!

You don't need to install any of those libraries since your program is not using them.

Your compile command can simply be:
gcc -o demo main.c

Then run it:
./demo

A better compile command, with a more recent C standard and higher warning level, is:
gcc -std=c99 -Wall -o demo main.c

I don't know why, but using the commands you suggested above I get gybrish on my Lubuntu system. The terminal outputs:

1 : �Z��
2: �Z��
3: �Z��

What the hell? It appears that the functions fscanf and fgets aren't doing their job properly... How do I get this to work?

EDIT:
Now that I think about it, I guess the file is opening. Are you sure it contains text?

Yep! The problem was that the file was empty. Sorted now. Thank you!

Actually, each read of the file needs a check to test if the end-of-file was reached. So your program might be written like this:

Code:

#include <stdio.h>
#include <stdlib.h>

int main() {
   FILE *fp = fopen("gcc_args.c", "r");
   if (fp == NULL) {
       perror("fopen");
       exit(EXIT_FAILURE);
   }
   
   char buf[255];
   int i = 0;

   while (fgets(buf, sizeof buf, fp) != NULL)
       printf("%3d: %s", ++i, buf);

   fclose(fp);
   
   return 0;
}

Thanks! That helped