# PR_Writev

Writes data to a socket from multiple buffers.

## Syntax

```{code}
#include <prio.h>

PRInt32 PR_Writev(
  PRFileDesc *fd,
  PRIOVec *iov,
  PRInt32 size,
  PRIntervalTime timeout);

#define PR_MAX_IOVECTOR_SIZE 16
```

### Parameters

The function has the following parameters:

`fd`

: A pointer to a {ref}`PRFileDesc` object for a socket.

`iov`

: An array of `PRIOVec` structures that describe the buffers to write
  from.

`size`

: Number of `PRIOVec` structures in the `iov` array. The value of
  this parameter must not be greater than `PR_MAX_IOVECTOR_SIZE`. If
  it is, the function will fail and the error will be set to
  `PR_BUFFER_OVERFLOW_ERROR`.

`timeout`

: A value of type {ref}`PRIntervalTime` describing the time limit for
  completion of the entire write operation.

### Returns

One of the following values:

- A positive number indicates the number of bytes successfully written.
- The value -1 indicates that the operation failed. The reason for the
  failure can be obtained by calling {ref}`PR_GetError`.

## Description

The thread calling {ref}`PR_Writev` blocks until all the data is written or
the write operation fails. Therefore, the return value is equal to
either the sum of all the buffer lengths (on success) or -1 (on
failure). Note that if {ref}`PR_Writev` returns -1, part of the data may
have been written before an error occurred. If the timeout parameter is
not `PR_INTERVAL_NO_TIMEOUT` and all the data cannot be written in the
specified interval, {ref}`PR_Writev` returns -1 with the error code
`PR_IO_TIMEOUT_ERROR`.

This is the type definition for `PRIOVec`:

```{code}
typedef struct PRIOVec {
  char *iov_base;
  int iov_len;
} PRIOVec;
```

The `PRIOVec` structure has the following fields:

`iov_base`

: A pointer to the beginning of the buffer.

`iov_len`

: The size of the buffer.