fread

fread is a standard C library function that reads data from a file stream into memory. It is declared in stdio.h as size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream).

The function reads up to nmemb elements, each of size bytes, from the stream into the array pointed to by ptr. It returns the number of elements successfully read, which may be less than nmemb if end-of-file is encountered or if a read error occurs. If size or nmemb is zero, the call returns 0. The actual number of bytes read is the return value multiplied by size.

fread is binary-safe in the sense that it reads raw bytes without interpreting them. However, on platforms that support text mode files, translation of newline characters can occur when a stream is opened in text mode, which can affect the number of bytes read. The FILE* object provides buffering, so fread may fetch data from the underlying source in larger chunks than requested.

To distinguish between end-of-file and error, use feof and ferror. On error, errno may be set. fread is intended for bulk, unformatted input and is commonly used to read binary data or large blocks of data, as opposed to formatted input functions such as fscanf or line-oriented input such as fgets. A typical usage pattern is to repeatedly call fread with a fixed-size buffer and process the portion actually read until it returns 0, then check for errors or end-of-file.