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C/C++ API Documentation | 2026.1

# ClientApi::DefineUser( const char *, Error * )

Sets `P4USER` in the Windows registry and applies the setting immediately.

Virtual? | No |
Class | `ClientApi` |
Arguments | `const char *c` | the new `P4USER` setting
| `Error *e` | an `Error` object
Returns | `void` |

## Notes

To make the new `P4USER` setting apply to the next command executed with `Run()`, `DefineUser()` sets the value in the registry and then calls `SetUser()`.

## Example

The following code illustrates how this method might be used to make a Windows client application start up with a default `P4USER` setting.

    client.Init( &e );
    client.DefineUser( "default_user", &e );

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