PHP：具有未定义常量的switch语句

Question

Just a quick question regarding how PHP handles switch statements.

If I had the following code

switch (APPLICATION_ENVIRONMENT) {
    case 'production':
        echo 'production';
        break;
    case 'stage':
        echo 'stage';
        break;
    default: //dev
        echo 'dev';
}

would this still evaluate to default if APPLICATION_ENVIRONMENT was not defined anywhere? Or would it throw out an error? Looking at existing source in the application im running, whoever has done this previously has done an if(defined()) on the constant first to check if it exists, which is a waste if switch can eval that properly for me

Thanks DJ

Answer 1

If undefined, APPLICATION_ENVIRONMENT would be interpreted by PHP as the string "APPLICATION_ENVIRONMENT", and so would fall through to the default since the string "APPLICATION_ENVIRONMENT" is not one of your defined switch cases.

echo APPLICATION_ENVIRONMENT;

PHP Notice: Use of undefined constant APPLICATION - assumed 'APPLICATION_ENVIRONMENT' in php shell code on line 1

PHP will issue a notice when it encounters an undefined constant, and, for better or worse, will process it under the assumption that you intended to quote it as a string.