C Library - fgetpos() function

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The C library fgetpos(FILE *stream, fpos_t *pos) function gets the current file position of the stream and writes it to pos. It stores the position in a variable of type fpos_t. This function is useful when you need to save a specific location in a file and return to it later.

Syntax

Following is the C library syntax of the fgetpos() function −

int fgetpos(FILE *stream, fpos_t *pos);

Parameter

This function accepts two parameter −

• FILE *stream: A pointer to a FILE object that identifies the stream.
• fpos_t *pos: A pointer to an object of type fpos_t where the position is stored.

Return Value

The fgetpos() function returns 0 on success and it returns a non-zero value on failure.

Example 1: Simple Position Fetch

This example shows how to get and print the current position in a file.

Below is the illustration of C library fgetpos() function.

#include <stdio.h>

int main() {
   FILE *file = fopen("example1.txt", "w+");
   if (file == NULL) {
       perror("Failed to open file");
       return 1;
   }

   fputs("Hello, World!", file);
   fpos_t pos;
   
   // Get the current file position
   if (fgetpos(file, &pos) != 0) {
       perror("fgetpos failed");
       fclose(file);
       return 1;
   }
   
   printf("Current position: %ld\n", (long)pos);

   fclose(file);
   return 0;
}

Output

The above code wites "Hello, World!" to the file and fetches the position, which is 13 because "Hello, World!" has 13 characters including the space and punctuation.−

Current position: 13

Example 2: Reading and Rewinding in a File

In this example it shows reading from a file, saving the position, and then rewinding to the saved position.

#include <stdio.h>

int main() {
   FILE *file = fopen("example3.txt", "w+");
   if (file == NULL) {
       perror("Failed to open file");
       return 1;
   }

   fputs("Line 1\nLine 2\nLine 3\n", file);
   fpos_t pos;
   
   // Rewind to the start of the file
   rewind(file);
   
   char buffer[20];
   fgets(buffer, sizeof(buffer), file);
   printf("First read: %s", buffer);
   
   // Save the current position after reading the first line
   if (fgetpos(file, &pos) != 0) {
       perror("fgetpos failed");
       fclose(file);
       return 1;
   }
   
   fgets(buffer, sizeof(buffer), file);
   printf("Second read: %s", buffer);
   
   // Return to the saved position
   if (fsetpos(file, &pos) != 0) {
       perror("fsetpos failed");
       fclose(file);
       return 1;
   }
   
   fgets(buffer, sizeof(buffer), file);
   printf("Re-read after fsetpos: %s", buffer);

   fclose(file);
   return 0;
}

Output

After execution of above code, it writes multiple lines to a file, reads the first line, saves the position, reads the second line, then returns to the saved position and reads the second line again.

First read: Line 1
Second read: Line 2
Re-read after fsetpos: Line 2