Sublime text not flushing automatically, c code

Question

I'm trying to execute my compiled c file from ST using this build system:

{
   "working_dir" : "$file_path",


   "selector": "source.x",

   "shell_cmd": "${file_path}/${file_base_name}.x",
   "file_regex":  "^([^:]*):([0-9]+):[0-9]+: (?:error|note):"



}

however:

printf("hello world \n");

does not print during execution, but only when i quit the program (that's a big problem for me).

however:

 printf("hello world \n");
fflush(stdout);

Print immediately during exection.

Any idea ?