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# PR_GetUniqueIdentity
Asks the runtime to allocate a unique identity for a layer identified by
the layer's name.
## Syntax
```{code}
#include <prio.h>
PRDescIdentity PR_GetUniqueIdentity(const char *layer_name);
```
### Parameter
The function has the following parameter:
`layer_name`
: The string associated with the creation of a layer's identity.
### Returns
The function returns one of the following values:
- If successful, the {ref}`PRDescIdentity` for the layer associated with
the string specified in the layer named `layer_name`.
- If the function cannot allocate enough dynamic memory, it fails and
returns the value `PR_INVALID_IO_LAYER` with the error code
`PR_OUT_OF_MEMORY_ERROR`.
## Description
A string may be associated with a layer when the layer is created.
{ref}`PR_GetUniqueIdentity` allocates a unique layer identity and
associates it with the string. The string can be subsequently passed to
{ref}`PR_CreateIOLayerStub` to create a new file descriptor of that layer.
Call {ref}`PR_GetUniqueIdentity` only once for any particular layer name.
If you're creating a custom I/O layer, cache the result, and then use
that cached result every time you call {ref}`PR_CreateIOLayerStub`.