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. For details, refer to Chapter 1, "Development
Concepts."
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.
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 Figure 9.4).
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."
