rewind() in C

The rewind() function is a standard library function declared in the <stdio.h> header file. It is used to move the file position indicator back to the beginning of a file without closing and reopening it.

• It resets the file pointer to the start of the file, allowing the file to be read or written again from the beginning.
• It also clears the end-of-file (EOF) and error indicators associated with the file stream.
• It is commonly used when the same file needs to be processed multiple times within a program.

#include <stdio.h>

int main() {
    
    FILE *fptr = fopen("file.txt", "w+");
    
    // Write data to file
    fprintf(fptr, "Hello, GFG!");
    
    // Rewind fptr to the beginning
    rewind(fptr);

    // Read data from file
    char ch;
    while ((ch = fgetc(fptr)) != EOF) {
        printf("%c", ch);
    }

    fclose(fptr);
    return 0;
}

Hello, GFG!

Explanation

• fprintf() first writes "Hello, GFG!" to the file, which moves the file pointer to the end of the written content.
• rewind() resets the file pointer to the beginning of the file, allowing fgetc() to read the file from the start one character at a time.

Syntax

void rewind(FILE *stream);

Parameters

• stream: Pointer to the file whose position indicator is to be reset.

Return Value

• The rewind() function does not return any value (void).
• After execution, the file position is reset to the beginning, and the EOF and error flags are cleared.

Working

The rewind() function resets the file position indicator to the beginning of the specified file.

• Open or access a file using a valid FILE* pointer.
• Perform read or write operations, which move the file pointer from its initial position.
• Call rewind() to move the file pointer back to the beginning of the file.
• Continue reading from or writing to the file without reopening it.

Advantages

The rewind() function provides a simple way to reuse an already opened file.

• Resets the file pointer to the beginning without reopening the file.
• Clears the end-of-file (EOF) and error indicators automatically.
• Useful when the same file needs to be read or processed multiple times.

Limitations

Although rewind() is convenient, it has a few limitations.

• It always resets the file pointer to the beginning and cannot move to an arbitrary position.
• It does not return a status value, so errors cannot be detected directly.
• It works only with valid file streams opened using file handling functions.

rewind() vs fseek()