# Use a string user ID (/en/realtime-media/rtc-server-sdk/build/build-core-media-features/stringuid)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

The Agora Server Gateway supports both integer and string user IDs. This page shows you how to use string user IDs.

## Implementation [#implementation]

1. When initializing the `IAgoraService` instance, set `AgoraServiceConfiguration.useStringUid` to `true`.

   ```cpp
   // Create an IAgoraService object
   auto service = createAgoraService();
   // Initialize the IAgoraService object
   agora::base::AgoraServiceConfiguration config;
   // Set Agora App ID
   config.appId = appid;
   // Enable the audio processing module
   config.enableAudioProcessor = enableAudioProcessor;
   // Disable the audio device module 
   // Normally, audio capture or playback devices are not connected to a server
   config.enableAudioDevice = enableAudioDevice;
   // Whether to enable video
   config.enableVideo = enableVideo;
   // Enable user IDs in string format (the characters can be digits, letters, or special symbols) 
   config.useStringUid = enableUseStringUid;
   if (service->initialize(config) != agora::ERR_OK) {
       return nullptr;
   }
   ```

2. Call `connect` to connect to the Video SDK channel.

   ```cpp
   if (connection->connect(options.appId.c_str(), options.channelId.c_str(),
                           options.userId.c_str())) {
       AG_LOG(ERROR, "Failed to connect to Agora channel!");
       return -1;
   }
   ```

## Limitations [#limitations]

* Enabling string user IDs when initializing `IAgoraService` takes effect only after connecting to a channel. Before connection, the SDK defaults to integer user IDs. This means that you cannot subscribe to non-numeric user IDs. Ensure that any user ID you `subscribe` to before connection include only numbers. After connection, you can subscribe to user IDs with other characters.

* String user IDs can only communicate with other string user IDs. If a channel contains both string and integer user IDs, unknown errors may occur.

* Unlike integer user IDs, you must specify the string `userId` parameter in the `connect` method. If you leave it unset, you receive an error.

* A string user ID must be unique within each channel.

## Supported character set [#supported-character-set]

* Integer user IDs

  * 10 digits: 0-9

* String user IDs

  * Lowercase English letters
  * Uppercase English letters
  * 10 digits: 0-9
  * The space character
  * "!", "#", "$", "%", "&", "(", ")", "+", "-", ":", ";", "\<", "=", ".", ">", "?", "@", "\[", "]", "^", "\_", " \{", "}", "|", "\~", ","