# PR_MemMap

Maps a section of a file to memory.

## Syntax

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

void* PR_MemMap(
  PRFileMap *fmap,
  PRInt64 offset,
  PRUint32 len);
```

### Parameters

The function has the following parameters:

`fmap`

: A pointer to the file-mapping object representing the file to be
  memory-mapped.

`offset`

: The starting offset of the section of file to be mapped. The offset
  must be aligned to whole pages.

`len`

: Length of the section of the file to be mapped.

### Returns

The starting address of the memory region to which the section of file
is mapped. Returns `NULL` on error.

## Description

{ref}`PR_MemMap` maps a section of the file represented by the file mapping
`fmap` to memory. The section of the file starts at `offset` and has
the length `len`.

When the file-mapping memory region is no longer needed, it should be
unmapped with a call to {ref}`PR_MemUnmap`.