Capítulo 32_ Accepting Arguments

Tabla de contenidos
Determining the Number of Arguments
Retrieving Arguments
Old way of retrieving arguments (deprecated)
Dealing with a Variable Number of Arguments/Optional Parameters
Accessing Arguments
Dealing with Arguments Passed by Reference
Assuring Write Safety for Other Parameters

One of the most important issues for language extensions is accepting and dealing with data passed via arguments_ Most extensions are built to deal with specific input data (or require parameters to perform their specific actions), and function arguments are the only real way to exchange data between the PHP level and the C level_ Of course, there's also the possibility of exchanging data using predefined global values (which is also discussed later), but this should be avoided by all means, as it's extremely bad practice_

PHP doesn't make use of any formal function declarations; this is why call syntax is always completely dynamic and never checked for errors_ Checking for correct call syntax is left to the user code_ For example, it's possible to call a function using only one argument at one time and four arguments the next time _ both invocations are syntactically absolutely correct_

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 32_1)_

Figura 32_1_ WRONG_PARAM_COUNT in action_

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_"