C/stdio.h/setbuf

    
//Header file:     #include <stdio.h>  
//Declaration:  void setbuf(FILE *stream, char *buf); 
  
#include <stdio.h>
int main ()
{
  char buffer[BUFSIZ];
  FILE *fp1, *fp2;
  fp1=fopen ("test.txt","w");
  fp2=fopen ("test2.txt","a");
  setbuf ( fp1 , buffer );
  fputs ("This is sent to a buffered stream",fp1);
  fflush (fp1);
  setbuf ( fp2 , NULL );
  fputs ("This is sent to an unbuffered stream",fp2);
  //Set buf to null to turn off buffering.
  //The buffer must be BUFSIZ characters long.
  //BUFSIZ is defined in <stdio.h>.  

  fclose (fp1);
  fclose (fp2);
  return 0;
}