Function freopen () in C

This function may be used for opening a file in different modes. The function prototype may be written in the following manner:

FILE *freopen(const char* filename, const char* mode, FILE* stream);

The function opens the file whose name is the string filename in a mode pointed to by mode and associates it with the stream pointed to by stream. The function returns pointer to stream if successful otherwise it returns a NULL pointer. Program provides an illustration for re-opening a file in different modes.

#include <stdio.h> 
 #include <stdlib.h> 
 void main() 
 { 
    FILE* fptr; //filestream 
    fptr = fopen ("Student_file","w"); 
    clrscr(); 
    if( fptr ==NULL) //test if fopen () fails to open file. 
      { 
          printf("File could not be opened."); 
          exit (1); 
      } 
    else 
          printf("File Student_fileis open for writing.\n"); 
          freopen ("Student_file","a", fptr);  
                      /* reopen filefor appending*/ 
          if(fptr ==NULL) 
             printf( "Failed to reopen"); 
          else 
             printf ("Student_file is opened in append mode.\n"); 
             freopen ("Student_file","r", fptr); 
                    /* reopen filefor appending*/ 
             if(fptr ==NULL) 
                printf( "Failed to reopen"); 
             else 
                printf("The file is open for reading.\n"); 
                fclose(fptr); 
 }