When using PHP5.4 and above, when calling the function, Parse error: syntax error, unexpected '&' or PHP Fatal error: Call-time pass-by-reference has been removed. This is because passing parameters by reference when calling the function is deprecated because it affects the neatness of the code. If the function's parameters are not declared to be passed as references, then it can modify its parameters in a documented manner. To prevent side effects, it is best to specify in the function declaration which parameters are passed by reference. Therefore, the PHP core configuration allows_call_time_pass_reference was removed in PHP 5.4. When the parameter is a reference parameter in the called function definition, the parameter can be directly passed without adding parameters through the reference symbol "&".
For example, a function definition is foo($arg1,$arg2) before PHP5.4. If you want the second parameter to be referenced and passed when called, it should be foo($v1,&$v2) when called. If you want to pass a reference after PHP5.4, you need to specify which parameter to pass a reference when defining the function, such as foo($arg1,&$arg2), and call it directly when calling: foo($v1,$v2).