# PR_GetSpecialFD

Gets the file descriptor that represents the standard input, output, or
error stream.

## Syntax

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

PRFileDesc* PR_GetSpecialFD(PRSpecialFD id);
```

### Parameter

The function has the following parameter:

`id`

: A pointer to an enumerator of type `PRSpecialFD`, indicating the
  type of I/O stream desired: `PR_StandardInput`,
  `PR_StandardOutput`, or `PR_StandardError`.

### Returns

If the `id` parameter is valid, {ref}`PR_GetSpecialFD` returns a file
descriptor that represents the corresponding standard I/O stream.
Otherwise, {ref}`PR_GetSpecialFD` returns `NULL` and sets the error to
`PR_INVALID_ARGUMENT_ERROR`.

## Description

Type `PRSpecialFD` is defined as follows:

```{code}
typedef enum PRSpecialFD{
   PR_StandardInput,
   PR_StandardOutput,
   PR_StandardError
} PRSpecialFD;
```

`#define PR_STDIN PR_GetSpecialFD(PR_StandardInput)`
`#define PR_STDOUT PR_GetSpecialFD(PR_StandardOutput)`
`#define PR_STDERR PR_GetSpecialFD(PR_StandardError)`

File descriptors returned by {ref}`PR_GetSpecialFD` are owned by the
runtime and should not be closed by the caller.