The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008
Copyright © 2001-2008 The IEEE and The Open Group


sys/uio.h - definitions for vector I/O operations


[XSI] [Option Start] #include <sys/uio.h> [Option End]


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.


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>.




<limits.h> , <sys/types.h>

XSH read , readv , write , writev


First released in Issue 4, Version 2.

Issue 6

Text referring to scatter/gather I/O is added to the DESCRIPTION.

End of informative text.


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