Arduino - Concatanate Two String in MQTT

Projects General Guidance
1

Hello
i am trying to combine two strings in two varibles (string class) and publish using client.publish. any tutorial or any example any one can give??? searched google for ages

2

Combining C strings - Sök (bing.com)

First try. The first find looks promising.

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      String sTopic = "";
      sTopic.reserve( 35 );
      sTopic.concat( String(px_eData.SunRiseHr) + "," );
      sTopic.concat( String(px_eData.SunRiseMin) + "," );
      sTopic.concat( String(px_eData.SunSetHr) + "," );
      sTopic.concat( String(px_eData.SunSetMin) + "," );
      sTopic.concat( String(px_eData.DawnHr) + "," );
      sTopic.concat( String(px_eData.DawnMin) + "," );
      sTopic.concat( String(px_eData.TransitHr) + "," );
      sTopic.concat( String(px_eData.TransitMin) );
      xSemaphoreTake( sema_MQTT_KeepAlive, portMAX_DELAY );
      MQTTclient.publish( topicSRSSDDT, sTopic.c_str() );
      xSemaphoreGive( sema_MQTT_KeepAlive );
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is there a much easier way???

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