How to remove line breaks after "ctime" in C program?

Question

Please bear with me since I'm still really new to C programming. When I run this code:

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

int main(void)
{
    while (1) {
        time_t mytime;
        mytime = time(NULL);
        printf("%s Hello world\n", ctime(&mytime));
        sleep(1);
    }
    return 0;
}

The output always looks like this:

Wed Jan 18 02:32:32 2017
 Hello world
Wed Jan 18 02:32:33 2017
 Hello world
Wed Jan 18 02:32:34 2017
 Hello world

What I want is like this:

Wed Jan 18 02:32:32 2017 Hello world
Wed Jan 18 02:32:33 2017 Hello world
Wed Jan 18 02:32:34 2017 Hello world

How can I do that ?

Note: If I remove \n from printf("%s Hello world\n", ctime(&mytime)); it'll result like this:

Wed Jan 18 02:38:29 2017
 Hello worldWed Jan 18 02:38:30 2017
 Hello worldWed Jan 18 02:38:31 2017
 Hello worldWed Jan 18 02:38:32 2017
 Hello worldWed Jan 18 02:38:33 2017

Answer 1

The ctime function will return a pointer to a string which ends in a newline.

From the man page:

The call ctime(t) is equivalent to asctime(localtime(t)). It converts the calendar time t into a null-terminated string of the form "Wed Jun 30 21:49:08 1993\n"

If you don't want the newline, you need to save the pointer and remove the newline before printing.

char *t = ctime(&mytime);
if (t[strlen(t)-1] == '\n') t[strlen(t)-1] = '\0';
printf("%s Hello world\n", t);

Answer 2

Use strftime to format your own string:

#include <stdio.h>
#include <time.h>

int main(void)
{
    char buf[100];
    strftime(buf, 100, "%a %b %d %T %Y", localtime(&(time_t){time(NULL)}));
    printf("%s Hello world\n", buf);
}

For simple formatting tasks like the one in the question, you can spare yourself the printf and let strftime do all the work:

    strftime(buf, 100, "%a %b %d %T %Y Hello world\n",
             localtime(&(time_t){time(NULL)}));
    fputs(buf, stdout);

You should also check the return value of strftime, zero may indicate failure.