printf() function executes after time() function? C/C++

Question

I wrote the following program:

#include <cstdio>
#include <ctime>
int main()

{
time_t t;
int d;
printf("\nHello 1");    
    time(&t);           
    d=t;
    while (t-d<3) /*wait 3 seconds*/
    {
        time(&t);
    }
printf("\nHello 2");
    time(&t);
    d=t;
    while (t-d<3)  /*wait 3 seconds*/
    {
        time(&t);
    }
printf("\nHello 3");
return 0;
}

after build the program, i run it. The program waits 3 seconds to show the line "Hello 1".

why is it written first but executed later?

It looks like the execution is in-order but th output is buffered. Try adding `fflush(stdout);` just after each `printf` calls. — MikeCAT, Jun 10 '21 at 13:30
Put the `\n` after strings and not before, to force the line-buffered output. — Eugene Sh., Jun 10 '21 at 13:32
Move the '\n' to the end of the string. New line will flush the buffer — 0___________, Jun 10 '21 at 13:32
In general, put `'\n'` at the end of the line. Don't reflexively flush the output. Writing a newline will almost always be sufficient. — Pete Becker, Jun 10 '21 at 14:28

score 0 · Answer 1 · answered Jun 10 '21 at 13:33

0

On some OS, the output buffer stdout typically needs to be "flushed" in order to make what you print there appear on screen. The \n acts as a "flush" and that explains the behavior.

You can fix this by adding a fflush(stdout); call after each printf. This forces a screen update. Alternatively move the \n to the end of each line instead of at the beginning.

answered Jun 10 '21 at 13:33

Lundin

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Asked many times before – 0___________ Jun 10 '21 at 13:35
@0___________ Probably, but I'm not aware of a canonical dupe, especially not in C++. – Lundin Jun 10 '21 at 13:37
thank you, this is really helpful ! – Vip Boy Jun 10 '21 at 13:39

score 0 · Answer 2 · answered Jun 10 '21 at 13:35

0

Basically, you need to flush the buffer. So the simplest thing is to move from this: printf("\nHello 1"); to printf("Hello 1\n");

Try this https://onlinegdb.com/u5L2xtwgf

answered Jun 10 '21 at 13:35

Oussama Ben Ghorbel

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printf() function executes after time() function? C/C++

2 Answers2