C fseek() function

C library function - fseek()

The fseek() function change the current file position that is associated with stream to a new location within the file.


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

fseek() Parameters:

Name Description Required /Optional
stream Identifies an address for a file descriptor, which is an area of memory associated with an input or output stream. Required
offset Number of bytes to offset from whence Required
whence The new position, measured in bytes from the beginning of the file, shall be obtained by adding offset to the position specified by whence. Required

Return value from fseek()

  • The fseek() function shall return 0 if they succee,d otherwise, they shall return -1 and set errno to indicate the error.

Example: fseek() function

Following function opens a file test.txt for reading. After performing input operations,fseek() moves the file pointer to the beginning of the file.

#include <stdio.h>
#define  MAX_LEN  10
int main(void)
   FILE *stream;
   char buffer[MAX_LEN + 1];
   int  result;
   int  i;
   char ch;
   stream = fopen("test.txt", "r");
   for (i = 0; (i  < (sizeof(buffer)-1) &&
       ((ch = fgetc(stream)) != EOF) && (ch != '\n')); i++)
          buffer[i] = ch;
   result = fseek(stream, 0L, SEEK_SET);  /* moves the pointer to the */
                                          /* beginning of the file    */
   if (result == 0)
      printf("Pointer successfully moved to the beginning of the file.\n");
      printf("Failed moving pointer to the beginning of the file.\n");


Pointer successfully moved to the beginning of the file.

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C Programming: Tips of the Day

What's an object file in C?

An object file is the real output from the compilation phase. It's mostly machine code, but has info that allows a linker to see what symbols are in it as well as symbols it requires in order to work. (For reference, "symbols" are basically names of global objects, functions, etc.)

A linker takes all these object files and combines them to form one executable (assuming that it can, i.e.: that there aren't any duplicate or undefined symbols). A lot of compilers will do this for you (read: they run the linker on their own) if you don't tell them to "just compile" using command-line options. (-c is a common "just compile; don't link" option.)

Ref : https://bit.ly/3CbzF8M