Repositioning a File Pointer

 
int fseek(FILE *fstream, int offset, int whence);

The function sets the file pointer associated with fstream to a new position that is offsetbytes from the location specified by whence. The argument whence can have one of these values:

 
SEEK_SET // file's beginning
SEEK_CUR // current file position
SEEK_END // end of file

In the following example, fseek() is used to calculate a file's size in a portable manner:

 
long file_size (FILE *f);
{
 long cur_pos, length;
 cur_pos = ftell(f)
 fseek(f, 0, SEEK_END); // set pointer to end of file
 length=ftell(f); // offset in bytes from file's beginning
 fseek(f, cur_pos, SEEK_SET); // restore original position
 return length;
}