# PR_AttachSharedMemory

Attaches a memory segment previously opened with {ref}`PR_OpenSharedMemory`
and maps it into the process memory space.

## Syntax

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

```{code}
NSPR_API( void * )
  PR_AttachSharedMemory(
     PRSharedMemory *shm,
     PRIntn flags
);

/* Define values for PR_AttachSharedMemory(...,flags) */
#define PR_SHM_READONLY 0x01
```

### Parameters

The function has these parameters:

shm

: The handle returned from {ref}`PR_OpenSharedMemory`.

flags

: Options for mapping the shared memory. `PR_SHM_READONLY` causes the
  memory to be attached read-only.

### Returns

Address where shared memory is mapped, or `NULL` if an error occurs.
Retrieve the reason for the failure by calling {ref}`PR_GetError` and
{ref}`PR_GetOSError`.