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><H1
><A
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>Chapter 32. Accepting Arguments</A
></H1
><DIV
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><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="zend.arguments.html#zend.arguments.count"
>Determining the Number of Arguments</A
></DT
><DT
><A
HREF="zend.arguments.retrieval.html"
>Retrieving Arguments</A
></DT
><DT
><A
HREF="zend.arguments.deprecated-retrieval.html"
>Old way of retrieving arguments (deprecated)</A
></DT
><DT
><A
HREF="zend.arguments.variable.html"
>Dealing with a Variable Number of Arguments/Optional Parameters</A
></DT
><DT
><A
HREF="zend.arguments.access.html"
>Accessing Arguments</A
></DT
><DT
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>Dealing with Arguments Passed by Reference</A
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HREF="zend.arguments.write-safety.html"
>Assuring Write Safety for Other Parameters</A
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>&#13;   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. 
  </P
><P
>&#13;   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.
  </P
><DIV
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><H1
CLASS="section"
><A
NAME="zend.arguments.count"
></A
>Determining the Number of Arguments</H1
><P
>&#13;    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
    <TT
CLASS="literal"
>ZEND_NUM_ARGS</TT
> 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, <TT
CLASS="envar"
>ht</TT
>, which is passed in the
    <TT
CLASS="literal"
>INTERNAL_FUNCTION_PARAMETERS</TT
> list. As
    <TT
CLASS="envar"
>ht</TT
> itself now contains the number of arguments that
    have been passed to the function, <TT
CLASS="literal"
>ZEND_NUM_ARGS</TT
>
    has been stripped down to a dummy macro (see its definition in
    <TT
CLASS="filename"
>zend_API.h</TT
>). But it's still good practice to
    use it, to remain compatible with future changes in the call
    interface. <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>Note:</I
></SPAN
> The old PHP equivalent of
    this macro is <TT
CLASS="literal"
>ARG_COUNT</TT
>.
   </P
><P
>&#13;    The following code checks for the correct number of arguments:
    <TABLE
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><TR
><TD
><PRE
CLASS="programlisting"
>if(ZEND_NUM_ARGS() != 2) WRONG_PARAM_COUNT;</PRE
></TD
></TR
></TABLE
> 
    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 <TT
CLASS="literal"
>WRONG_PARAM_COUNT</TT
>,
    which can be used to generate a standard error message (see <A
HREF="zend.arguments.html#fig.wrong-param-count"
>Figure 32-1</A
>).
   </P
><DIV
CLASS="figure"
><A
NAME="fig.wrong-param-count"
></A
><P
><B
>Figure 32-1. <TT
CLASS="literal"
>WRONG_PARAM_COUNT</TT
> in action.</B
></P
><P
><IMG
SRC="figures/Extending_Zend_3_wrong_parameter_count.png"></P
></DIV
><P
>&#13;    This macro prints a default error message and then returns to the caller.
    Its definition can also be found in <TT
CLASS="filename"
>zend_API.h</TT
> and looks
    like this: 
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><PRE
CLASS="programlisting"
>ZEND_API void wrong_param_count(void);

#define WRONG_PARAM_COUNT { wrong_param_count(); return; }</PRE
></TD
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>
    As you can see, it calls an internal function
    named <B
CLASS="function"
>wrong_param_count()</B
> that's responsible for printing
    the warning. For details on generating customized error
    messages, see the later section "Printing Information."
   </P
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