C/stdio.h/freopen

    
//Header file:     #include <stdio.h>  
//Declaration:     FILE *freopen(const char *fname, const char *mode, FILE *stream); 
//Return:          returns a pointer to stream on success or a null pointer on failure. 
//Legal Values for the mode Parameter
   
//Mode             Meaning
//"r":             Open text file for reading 
//"w":             Create a text file for writing 
//"a":             Append to text file 
//"rb":            Open binary file for reading 
//"wb":            Create binary file for writing 
//"ab":            Append to a binary file 
//"r+":            Open text file for read/write 
//"w+":            Create text file for read/write 
//"a+":            Open text file for read/write 
//"rb+" or "r+b":  Open binary file for read/write 
//"wb+" or "w+b":  Create binary file for read/write 
//"ab+" or "a+b":  Open binary file for read/write 

  

  #include <stdio.h>
  #include <stdlib.h>
  int main(void)
  {
    FILE *fp;
    printf("This will display on the screen.\n");
    if((fp=freopen("OUT", "w" ,stdout))==NULL) {
      printf("Cannot open file.\n");
      exit(1);
    }
    printf("This will be written to the file OUT.");
    fclose(fp);
    return 0;
  }