In response to your answer: why don't you think it is convenient? As you already noticed, you can use the enum values directly in your sketch.

Anyway, it is better to use a switch statement:

Serial.write("ODB State: ");
switch (odb.getState())
{ 
case ODB_DISCONNECTED: 
    Serial.write("Disconnected");
    break;

case OBD_CONNECTING:
    Serial.write("Connecting");
    break;

case OBD_CONNECTED:
    Serial.write("Connected");
    break;

case OBD_FAILED:
    Serial.write("Failed");
    break;

default:
    // Error case
    break;
}
 
Serial.write("\n");

This way, whenever the enum is changed (e.g. added items), you automatically fall into the error state, so you know you have to adapter the code.

In response to your answer: why don't you think it is convenient? As you already noticed, you can use the enum values directly in your sketch.

Anyway, it is better to use a switch statement:

Serial.write("ODB State: ");
switch (odb.getState()) {
  case ODB_DISCONNECTED: 
    Serial.write("Disconnected");
    break;

  case OBD_CONNECTING:
    Serial.write("Connecting");
    break;

  case OBD_CONNECTED:
    Serial.write("Connected");
    break;

  case OBD_FAILED:
    Serial.write("Failed");
    break;

  default:
    // Error case
    break;
}
Serial.write("\n");

This way, whenever the enum is changed (e.g. added items), you automatically fall into the error state, so you know you have to adapter the code.