Your company here — click to reach over 10,000 unique daily visitors

sys_uio.h - Man Page

definitions for vector I/O operations


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <sys/uio.h>


The <sys/uio.h> header shall define the iovec structure, which shall include at least the following members:

void   *iov_base  Base address of a memory region for input or output.
size_t  iov_len   The size of the memory pointed to by iov_base.

The <sys/uio.h> header uses the iovec structure for scatter/gather I/O.

The <sys/uio.h> header shall define the ssize_t and size_t types as described in <sys/types.h>.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

ssize_t readv(int, const struct iovec *, int);
ssize_t writev(int, const struct iovec *, int);

The following sections are informative.

Application Usage

The implementation can put a limit on the number of scatter/gather elements which can be processed in one call. The symbol {IOV_MAX} defined in <limits.h> should always be used to learn about the limits instead of assuming a fixed value.


Traditionally, the maximum number of scatter/gather elements the system can process in one call were described by the symbolic value {UIO_MAXIOV}. In IEEE Std 1003.1-2001 this value is replaced by the constant {IOV_MAX} which can be found in <limits.h>.

Future Directions


See Also

<limits.h>, <sys_types.h>

The System Interfaces volume of POSIX.1-2017, read(), readv(), write(), writev()

Referenced By

read(3p), readv(3p), sys_socket.h(0p), write(3p), writev(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual