fseek() in C

The fseek() function in C is used to move the file pointer to a specific position in a file. This allows for reading or writing data at a particular location within the file. It is a part of the standard input/output library.

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

Parameters

• stream: A pointer to the file object.
• offset: The number of bytes to move the file pointer. It can be positive, negative, or zero.
• whence: The reference position for offset. It can have the following values:
  • SEEK_SET: Beginning of the file.
  • SEEK_CUR: Current position of the file pointer.
  • SEEK_END: End of the file.

The function returns 0 on success and a non-zero value on failure.

Example: Using fseek()

                            
#include <stdio.h>
int main() 
{
    FILE *file = fopen("example.txt", "w+");
    if (file == NULL) {
        printf("Error opening file\n");
        return 1;
    }

    // Write data to the file
    fputs("Hello, world!", file);

    // Move the file pointer to the beginning
    fseek(file, 0, SEEK_SET);

    // Read and print the data
    char buffer[50];
    if (fgets(buffer, sizeof(buffer), file) != NULL) {
        printf("Data: %s\n", buffer);
    }             
            
    fclose(file);
    return 0;
}
                            
                        

Key Points

• The fseek() function allows random access to a file by moving the file pointer.
• The offset parameter specifies the number of bytes to move.
• The whence parameter determines the reference point for the movement:
  • SEEK_SET: From the beginning of the file.
  • SEEK_CUR: From the current position.
  • SEEK_END: From the end of the file.
• The function returns 0 if successful or a non-zero value if an error occurs.