C - write() system call prints gibberish instead of pid_t

Question

The following code:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
    pid_t mypid = getpid();
    write(1, &mypid, sizeof(pid_t));
    return 0;
}

Prints gibberish instead of actual pid. Why?

Because you are not sending text to `stdout`. `write` is a binary output function. Try `printf()`. — Weather Vane, Dec 11 '15 at 23:25

Fantastic Mr Fox · Accepted Answer · 2015-12-14T16:06:35.330

5

write(.. will not print formatted text, but rather binary output directly to a file descriptor.

Just use printf or fprintf:

fprintf(stdout, "%d", (int) mypid);

edited Dec 14 '15 at 16:06

answered Dec 11 '15 at 23:29

Fantastic Mr Fox

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By the way, the `fprintf` only works if `pid_t` is in fact `signed int`. Probably safer to cast it. – Nate Eldredge Dec 12 '15 at 03:16

C - write() system call prints gibberish instead of pid_t

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