C library function - fsetpos()

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Description

The C library function int fsetpos(FILE *stream, const fpos_t *pos) sets the file position of the given stream to the given position. The argument pos is a position given by the function fgetpos.

Declaration

Following is the declaration for fsetpos() function.

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

Parameters

  • stream -- This is the pointer to a FILE object that identifies the stream.

  • pos -- This is the pointer to a fpos_t object containing a position previously obtained with fgetpos.

Return Value

This function returns zero value if succesfull, else it returns a nonzero value and sets the global variable errno to a positive value, which can be interpreted with perror.

Example

The following example shows the usage of fsetpos() function.

#include <stdio.h>

int main ()
{
   FILE *fp;
   fpos_t position;

   fp = fopen("file.txt","w+");
   fgetpos(fp, &position);
   fputs("Hello, World!", fp);
  
   fsetpos(fp, &position);
   fputs("This is going to override previous content", fp);
   fclose(fp);
   
   return(0);
}

Let us compile and run the above program, this will create a file file.txt which will have the following content. First of all we get the initial position of the file using fgetpos() function and then we write Hello, World! in the file but later we used fsetpos() function to reset the write pointer at the begining of the file and then over-write the file with the following content:

This is going to override previous content

Now let's the content of the above file using the following program:

#include <stdio.h>

int main ()
{
   FILE *fp;
   int c;

   fp = fopen("file.txt","r");
   while(1)
   {
      c = fgetc(fp);
      if( feof(fp) )
      {
          break ;
      }
      printf("%c", c);
   }
   fclose(fp);
   return(0);
}


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