C fseek() function

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The fseek() function is used to set the file pointer to the specified offset. It is used to write data into file at desired location.

Syntax:




int fseek(FILE *stream, long int offset, int whence)


There are 3 constants used in the fseek() function for whence: SEEK_SET, SEEK_CUR and SEEK_END.

Example:




#include <stdio.h>
void main(){  
   FILE *fp;  
  
   fp = fopen("myfile.txt","w+");  
   fputs("This is javatpoint", fp);  
    
   fseek( fp, 7, SEEK_SET );  
   fputs("Rama", fp);  
   fclose(fp);  
}


newfile.txt

This is Rama

EXAMPLE PROGRAM FOR FSEEK(), SEEK_SET(), SEEK_CUR(), SEEK_END() FUNCTIONS IN C:




#include <stdio.h>
int main ()
{
   FILE *fp;
   char data[60];
   fp = fopen ("test.c","w");
   fputs("Fresh2refresh.com is a programming tutorial website", fp);
   fgets ( data, 60, fp );
   printf(Before fseek - %s", data); 
 
   // To set file pointet to 21th byte/character in the file
   fseek(fp, 21, SEEK_SET);
   fflush(data);
   fgets ( data, 60, fp );
   printf("After SEEK_SET to 21 - %s", data);
 
   // To find backward 10 bytes from current position
   fseek(fp, -10, SEEK_CUR);
   fflush(data);
   fgets ( data, 60, fp );
   printf("After SEEK_CUR to -10 - %s", data);
 
   // To find 7th byte before the end of file
   fseek(fp, -7, SEEK_END); 
   fflush(data);
   fgets ( data, 60, fp );
   printf("After SEEK_END to -7 - %s", data);
 
   // To set file pointer to the beginning of the file
   fseek(fp, 0, SEEK_SET); // We can use rewind(fp); also
 
   fclose(fp);
   return 0;
}


OUTPUT:

Before fseek – Fresh2refresh.com is a programming tutorial website

After SEEK_SET to 21 – a programming tutorial website

After SEEK_CUR to -10 – sh.com is a programming tutorial website

After SEEK_END to -7 – website




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