fwrite

fwrite is a standard C library function used to write blocks of data from a memory buffer to a file stream. It is declared in stdio.h and is commonly used for writing binary data or large arrays of objects, as opposed to formatting functions like fprintf or snprintf.

Prototype and parameters: size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); The function writes nmemb items, each of size bytes, from the buffer pointed to by ptr to the given stream. The number of items successfully written is returned. The total number of bytes written is size * returned_nmemb.

Return value and error handling: If successful, fwrite returns nmemb. If an error occurs or the end of the file is reached for the stream, it may return a smaller value than nmemb. To determine whether writing failed, test the return value and, if needed, use ferror(stream) to check for an error condition. The feof function is generally used for input streams; its meaning on output streams is implementation-defined.

Notes and usage: fwrite writes to the stream’s internal buffer, and data may not be physically written to the underlying medium until the buffer is flushed. To ensure durability, call fflush(stream) or close the stream with fclose. In text mode on some platforms, newline translation may occur; for portable binary data, open the file in binary mode. In C++, fwrite is available via std::fwrite in <cstdio>, integrating with C++ streams when interoperation with C code is needed.