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C strange anomaly when writing to a file (usually works when writing to stdout)

I am very new to C, so please bear with me. I have been struggling with this for a very long time, and it was difficult for me to narrow down the cause of the error.

I noticed that when forcing the process and writing to a file (only the source process writes a strange thing to the file, the output is almost multiplied by the number of forks, it is difficult to explain, so I did a little test code where you can run, and this recreates the problem.

#include <stdio.h>
#include <stdlib.h>


void foo()
{
  FILE* file = fopen("test", "w");
  int i=3;
  int pid;
  while (i>0)
  {
    pid=fork();
    if(pid==0)
    {
      printf("Child\n");
      exit(0);
     }
    else if(pid > 0)
    {
      fputs("test\n", file);
      i=i-1;
     }
 }

}

int main()
{
  foo();
  exit(EXIT_SUCCESS);
}

Compile and run it once as is, and once with file=stdout. When writing to stdoutoutput:

test
test
test

But when writing to a file, the output is:

test
test
test
test
test
test

Also, if you add indexing and change ito a larger number, you may see some kind of pattern, but that does not help me.

, , , , . C, =).

.

+5
1

stdout ; , , . fflush() fork(), , .

+8

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