---
name: "fread"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/fread"
---

# fread(3)

binary stream input/output

## NAME

fread, fwrite - binary stream input/output

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdio.h>
```

**size\_t fread(**size\_t size, size\_t n;              **void** *ptr***\[restrict** *size* **\*** *n***\],**              **size\_t** *size***, size\_t** *n***,**              **FILE \*restrict** *stream***);** **size\_t fwrite(**size\_t size, size\_t n;              **const void** *ptr***\[restrict** *size* **\*** *n***\],**              **size\_t** *size***, size\_t** *n***,**              **FILE \*restrict** *stream***);**

## DESCRIPTION

The function **fread**() reads *n* items of data, each *size* bytes long, from the stream pointed to by *stream*, storing them at the location given by *ptr*.

The function **fwrite**() writes *n* items of data, each *size* bytes long, to the stream pointed to by *stream*, obtaining them from the location given by *ptr*.

For nonlocking counterparts, see [**unlocked\_stdio**(3)](/unlocked_stdio/3.md).

## RETURN VALUE

On success, **fread**() and **fwrite**() return the number of items read or written. This number equals the number of bytes transferred only when *size* is 1. If an error occurs, or the end of the file is reached, the return value is a short item count (or zero).

The file position indicator for the stream is advanced by the number of bytes successfully read or written.

**fread**() does not distinguish between end-of-file and error, and callers must use [**feof**(3)](/feof/3.md) and [**ferror**(3)](/ferror/3.md) to determine which occurred.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **fread**(), **fwrite**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

POSIX.1-2001, C89.

## EXAMPLES

The program below demonstrates the use of **fread**() by parsing /bin/sh ELF executable in binary mode and printing its magic and class:

```
$ ./a.out;
ELF magic: 0x7f454c46
Class: 0x02
```

### Program source

```
#include <stdcountof.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
    FILE           *fp;
    size_t         ret;
    unsigned char  buffer[4];
    fp = fopen("/bin/sh", "rb");
    if (!fp) {
        perror("fopen");
        return EXIT_FAILURE;
    }
    ret = fread(buffer, sizeof(*buffer), countof(buffer), fp);
    if (ret != countof(buffer)) {
        fprintf(stderr, "fread() failed: %zu\n", ret);
        exit(EXIT_FAILURE);
    }
    printf("ELF magic: %#04x%02x%02x%02x\n", buffer[0], buffer[1],
           buffer[2], buffer[3]);
    ret = fread(buffer, 1, 1, fp);
    if (ret != 1) {
        fprintf(stderr, "fread() failed: %zu\n", ret);
        exit(EXIT_FAILURE);
    }
    printf("Class: %#04x\n", buffer[0]);
    fclose(fp);
    exit(EXIT_SUCCESS);
}
```

## SEE ALSO

[**read**(2)](/read/2.md), [**write**(2)](/write/2.md), [**feof**(3)](/feof/3.md), [**ferror**(3)](/ferror/3.md), [**unlocked\_stdio**(3)](/unlocked_stdio/3.md)