Determining the Number of Arguments

Since PHP doesn't have formal function definitions with support for call syntax checking, and since PHP features variable arguments, sometimes you need to find out with how many arguments your function has been called. You can use the ZEND_NUM_ARGS macro in this case. In previous versions of PHP, this macro retrieved the number of arguments with which the function has been called based on the function's hash table entry, ht, which is passed in the INTERNAL_FUNCTION_PARAMETERS list. As ht itself now contains the number of arguments that have been passed to the function, ZEND_NUM_ARGS has been stripped down to a dummy macro (see its definition in zend_API.h). But it's still good practice to use it, to remain compatible with future changes in the call interface. Note: The old PHP equivalent of this macro is ARG_COUNT.

The following code checks for the correct number of arguments:

if(ZEND_NUM_ARGS() != 2) WRONG_PARAM_COUNT;

If the function is not called with two arguments, it exits with an error message. The code snippet above makes use of the tool macro WRONG_PARAM_COUNT, which can be used to generate a standard error message (see Figura 52-1).

This macro prints a default error message and then returns to the caller. Its definition can also be found in zend_API.h and looks like this:

ZEND_API void wrong_param_count(void); #define WRONG_PARAM_COUNT { wrong_param_count(); return; }

As you can see, it calls an internal function named wrong_param_count() that's responsible for printing the warning. For details on generating customized error messages, see the later section "Printing Information."