Strange behaviour of fork function

[manjuscripts]

The output of the below program is "hihi" as "hi" is printed by both parent and child process

#include<stdio.h>
main()
{
  printf("hi");
  fork();
}
 

where as the output below program is

#include<stdio.h>
main()
{
  printf("hi\n");  //observe the \n after hi
  fork();
}
 

is only "hi"

what's the reason?

[mac11]

The output of the below program is "hihi" as "hi" is printed by both parent and child process

#include<stdio.h>
main()
{
printf("hi");
fork();
}


where as the output below program is

#include<stdio.h>
main()
{
printf("hi\n"); //observe the \n after hi
fork();
}

is only "hi"

what's the reason?

your printing BEFORE the fork - so there is only 1 process to print "hi"
try

fork()
printf( "hi\n");

[manjuscripts]

your printing BEFORE the fork - so there is only 1 process to print "hi"
try

fork()
printf( "hi\n");

but why it's printing "hihi" in first program? i think there's something related to "\n" or buffer.

[svlsr2000]

but why it's printing "hihi" in first program? i think there's something related to "\n" or buffer.

Yes you are right. Printing in linux is implemented in such a way that nothing is printed till it encounters some special characters like '\n' or till program is about to terminate.

Once it is passed to stdin, buffer is cleared. But this buffer is also part of your address space so when you fork even this buffer is copied. Resulting in printing Hi twice.