6

When I run the below program, I do not get any output.

#include <stdio.h>

int main()
{
    printf("hello");
    while(1)
    {

    }   
    return 0;
}

whereas if i edit the printf command to add a '\n' character to the end of the string, then the expected output comes. what is going on in the first code? I simply cannot understand it.

DesirePRG
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  • call `fflush(stdout)` btw you have infinite loop. – Grijesh Chauhan Oct 09 '13 at 11:18
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    Output is buffered. You need either a `\n` at the end of the string to get it to print out, or use `fflush(stdout)` after your `printf` as @GrijeshChauhan suggested. There are other operations which flush the output buffer as well, such as an input function (`getchar` or `scanf`) but it's unclear from your code snippet what your loop is doing. – lurker Oct 09 '13 at 11:20
  • possible duplicate of [Why does program not execute final printf statement?](http://stackoverflow.com/questions/11277796/why-does-program-not-execute-final-printf-statement) – lurker Oct 09 '13 at 11:22

3 Answers3

11

This is because stdout is line buffered, i.e. the output is not written to the device (the terminal) until a full line has been collected.

You can call fflush(stdout); to force a flush of the buffer to the terminal. Do not try to flushing stdin by the way, that's not allowed.

unwind
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  • ok but why does the code work without the infinite loop and with the same printf as above then? – DesirePRG Oct 09 '13 at 11:22
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    When program terminates shortly after, the os would definitely flush output buffer sooner as opposed to no flush request and program being continued. – fkl Oct 09 '13 at 11:23
2

try 

printf("hello\n");

or 

printf("hello");
fflush(stdout)
Arnaud Denoyelle
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0

Use printf("hello\n");

For more info see answers to this question.

Community
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0xF1
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