_write

Syntax

#include <io.h> ssize_t _write(int fildes, const void *buf, size_t nbyte);

Description

This is a direct connection to the MS-DOS write function call, int 0x21, %ah = 0x40. No conversion is done on the data; it is written as raw binary data. This function can be hooked by the File-system extensions, see File System Extensions. If you don't want this, you should use _dos_write instead, see _dos_write.

Return Value

The number of bytes written, or -1 (and errno set) in case of failure.

Note that DOS doesn't return an error indication when the target disk is full; therefore if the disk fills up while the data is written, _write does not return -1, it returns the number of bytes it succeeded to write. If you need to detect the disk full condition reliably, call _write again to try to write the rest of the data. This will cause DOS to return zero as the number of written bytes, and then _write will return -1 and set errno to ENOSPC. The example below shows one way of doing this.

Portability

ANSI/ISO C	No
POSIX	No

Example

This example shows how to call _write in a way which ensures that errno will be set to ENOSPC if the target filesystem is or becomes full:

char *buf_ptr; /* the buffer to write */ size_t buf_len; /* the number of bytes to write */ int desc; /* the file descriptor to write to */ while (buf_len > 0) { int written = _write (desc, buf_ptr, buf_len); if (written <= 0) break; buf_ptr += written; buf_len -= written; }