fsetpos() is an I/O function that moves the file position indicator to the point specified by the position parameter. This function returns a zero value on success, otherwise returns a nonzero value and sets the global variable errno to a positive value.

    int fsetpos ( FILE * stream, const fpos_t * pos );

   #include <stdio.h>
   int main() 
   {
     FILE * str=fopen ("fsetposeg.txt","w");
     fpos_t pos;
     fgetpos (str, &pos);
     fputs ("It is a blue color box",str);
     fsetpos (str, &pos);
     fputs ("This", str);
     fclose (str);
     return 0;
   } 

    This is a blue color box

In the above example the "fsetpos()" is used to write a text "this" to the current file position of the specified stream.