C fread() Function

Last Updated : 21 Jul, 2026

The fread() function is a standard library function declared in the <stdio.h> header file. It is used to read binary data from a file and store it in a memory buffer.

  • It reads multiple elements from a file based on the specified element size and count.
  • It is commonly used to read arrays, structures, and other binary data from files.
  • On success, it returns the number of elements successfully read; if the return value is less than the requested count, it indicates an error or end-of-file.
C++ 
#include <stdio.h>

int main() {
    FILE *file;
    int buffer[5];

    // Open the binary file for reading
    file = fopen("input.bin", "rb");
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }

    // Read the integers from the file into the buffer
    fread(buffer, sizeof(int),5, file);

    // Print the integers that were read
    for (int i = 0; i < 5; i++) {
        printf("Element %d: %d\n", i + 1, buffer[i]);
    }

    // Close the file
    fclose(file);
    return 0;
}


Output

Element 1: 10
Element 2: 20
Element 3: 30
Element 4: 40
Element 5: 50

Here, input.bin file should contain the binary representation of the integers: 10, 20, 30, 40, 50.

Syntax

size_t fread(void *buffer, size_t size, size_t count, FILE *stream);

Parameters

  • buffer: Pointer to the memory block where the read data will be stored.
  • size: Size of each element to be read, in bytes.
  • count: Number of elements to read from the file.
  • stream: Pointer to the file from which the data will be read.

Return Value

  • Returns the number of elements successfully read from the file.
  • If the return value is less than count, it indicates that an error occurred or the end of the file was reached.
  • If size or count is zero, the function returns 0 without reading any data.

Working

The fread() function reads a specified number of elements from a file and stores them in the provided memory buffer.

  • Open the file using fopen() in read ("r" or "rb") mode.
  • Pass the buffer, element size, element count, and file pointer to fread().
  • The function reads the data and stores it in the buffer.
  • After reading, close the file using fclose().

Note: The fread() function cannot distinguish between an end-of-file condition and a read error on its own. Use the feof() function to check for end-of-file and ferror() to detect file read errors.

Advantages of fread()

The fread() function provides an efficient way to read data from files, especially binary files.

  • Reads multiple elements from a file in a single function call.
  • Efficient for reading arrays, structures, and other binary data.
  • Supports reading any data type by specifying the element size and count.
  • Automatically advances the file position after each read operation.

Limitations of fread()

Although fread() is useful for reading binary data, it has a few limitations.

  • It cannot distinguish between end-of-file and a read error on its own.
  • It is primarily intended for binary files and may not be suitable for formatted text input.
  • Reading structures directly may cause portability issues due to compiler-specific padding and alignment.
  • The programmer must allocate a buffer of sufficient size before calling fread().
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