Implementation status: partially implemented


#include <stdio.h>

size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);


The fwrite() function writes data from the array pointed to by ptr to the given stream. It puts down nmemb elements each of size size.


ptr - an array containing data,
size - a size of a single element,
nmemb - a number of elements,
stream - a stream to which data is put.

For each object, size calls are made to the fputc() function, taking the values (in order) from an array of unsigned char exactly overlaying the object. The file-position indicator for the stream (if defined) is advanced by the number of bytes successfully written. If an error occurs, the resulting value of the file-position indicator for the stream is unspecified.

The last data modification and last file status change timestamps of the file are marked for update between the successful execution of fwrite() and the next successful completion of a call to fflush() or fclose() on the same stream, or a call to exit() or abort().

Return value

The fwrite() function returns the number of elements successfully written, which may be less than nmemb if a write error is encountered. If size or nmemb is 0, fwrite() return 0 and the state of the stream remains unchanged. Otherwise, if a write error occurs, the error indicator for the stream is set, and errno is set to indicate the error.


[EAGAIN] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the write operation.
[EBADF] The file descriptor underlying stream is not a valid file descriptor open for writing.
[EFBIG] An attempt was made to write to a file that exceeds the maximum file size.
[EFBIG] An attempt was made to write to a file that exceeds the file size limit of the process.
[EFBIG] The file is a regular file and an attempt was made to write at or beyond the offset maximum.
[EINTR] The write operation was terminated due to the receipt of a signal, and no data was transferred.
[EIO] A physical I/O error has occurred, or the process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the calling thread is not blocking SIGTTOU, the process is not ignoring SIGTTOU, and the process group of the process is orphaned.
[ENOSPC] There was no free space remaining on the device containing the file.
[EPIPE] An attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal is also sent to the thread.
[ENOMEM] Insufficient storage space is available.
[ENXIO] A request was made of a nonexistent device, or the request was outside the capabilities of the device.

Implementation tasks

  • implement error handling,