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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Function arguments</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.functions.html">Functions</a></div> <div class="next" style="text-align: right; float: right;"><a href="functions.returning-values.html">Returning values</a></div> <div class="up"><a href="language.functions.html">Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="functions.arguments" class="sect1"> <h2 class="title">Function arguments</h2> <p class="simpara"> Information may be passed to functions via the argument list, which is a comma-delimited list of expressions. </p> <p class="para"> PHP supports passing arguments by value (the default), <a href="functions.arguments.html#functions.arguments.by-reference" class="link">passing by reference</a>, and <a href="functions.arguments.html#functions.arguments.default" class="link">default argument values</a>. <a href="functions.arguments.html#functions.variable-arg-list" class="link">Variable-length argument lists</a> are also supported, see also the function references for <a href="function.func-num-args.html" class="function">func_num_args()</a>, <a href="function.func-get-arg.html" class="function">func_get_arg()</a>, and <a href="function.func-get-args.html" class="function">func_get_args()</a> for more information. </p> <p class="para"> <div class="example"> <p><b>Example #1 Passing arrays to functions</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">takes_array</span><span style="color: #007700">(</span><span style="color: #0000BB">$input</span><span style="color: #007700">)<br />{<br /> echo </span><span style="color: #DD0000">"$input[0] + $input[1] = "</span><span style="color: #007700">, </span><span style="color: #0000BB">$input</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]+</span><span style="color: #0000BB">$input</span><span style="color: #007700">[</span><span style="color: #0000BB">1</span><span style="color: #007700">];<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <div id="functions.arguments.by-reference" class="sect2"> <h3 class="title">Making arguments be passed by reference</h3> <p class="simpara"> By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function). To allow a function to modify its arguments, they must be passed by reference. </p> <p class="para"> To have an argument to a function always passed by reference, prepend an ampersand (&) to the argument name in the function definition: </p> <p class="para"> <div class="example"> <p><b>Example #2 Passing function parameters by reference</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">add_some_extra</span><span style="color: #007700">(&</span><span style="color: #0000BB">$string</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$string </span><span style="color: #007700">.= </span><span style="color: #DD0000">'and something extra.'</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">$str </span><span style="color: #007700">= </span><span style="color: #DD0000">'This is a string, '</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">add_some_extra</span><span style="color: #007700">(</span><span style="color: #0000BB">$str</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">$str</span><span style="color: #007700">; </span><span style="color: #FF8000">// outputs 'This is a string, and something extra.'<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> </div> <div id="functions.arguments.default" class="sect2"> <h3 class="title">Default argument values</h3> <p class="para"> A function may define C++-style default values for scalar arguments as follows: </p> <p class="para"> <div class="example"> <p><b>Example #3 Use of default parameters in functions</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">(</span><span style="color: #0000BB">$type </span><span style="color: #007700">= </span><span style="color: #DD0000">"cappuccino"</span><span style="color: #007700">)<br />{<br /> return </span><span style="color: #DD0000">"Making a cup of $type.\n"</span><span style="color: #007700">;<br />}<br />echo </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">();<br />echo </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">(</span><span style="color: #0000BB">null</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">(</span><span style="color: #DD0000">"espresso"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> The output from the above snippet is: </p> <p class="para"> <div class="example-contents"><pre>Making a cup of cappuccino.Making a cup of .Making a cup of espresso. </pre></div> </p> <p class="para"> PHP also allows the use of <a href="language.types.array.html" class="type array">array</a>s and the special type <b><tt>NULL</tt></b> as default values, for example: </p> <p class="para"> <div class="example"> <p><b>Example #4 Using non-scalar types as default values</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">(</span><span style="color: #0000BB">$types </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"cappuccino"</span><span style="color: #007700">), </span><span style="color: #0000BB">$coffeeMaker </span><span style="color: #007700">= </span><span style="color: #0000BB">NULL</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$device </span><span style="color: #007700">= </span><span style="color: #0000BB">is_null</span><span style="color: #007700">(</span><span style="color: #0000BB">$coffeeMaker</span><span style="color: #007700">) ? </span><span style="color: #DD0000">"hands" </span><span style="color: #007700">: </span><span style="color: #0000BB">$coffeeMaker</span><span style="color: #007700">;<br /> return </span><span style="color: #DD0000">"Making a cup of "</span><span style="color: #007700">.</span><span style="color: #0000BB">join</span><span style="color: #007700">(</span><span style="color: #DD0000">", "</span><span style="color: #007700">, </span><span style="color: #0000BB">$types</span><span style="color: #007700">).</span><span style="color: #DD0000">" with $device.\n"</span><span style="color: #007700">;<br />}<br />echo </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">();<br />echo </span><span style="color: #0000BB">makecoffee</span><span style="color: #007700">(array(</span><span style="color: #DD0000">"cappuccino"</span><span style="color: #007700">, </span><span style="color: #DD0000">"lavazza"</span><span style="color: #007700">), </span><span style="color: #DD0000">"teapot"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="simpara"> The default value must be a constant expression, not (for example) a variable, a class member or a function call. </p> <p class="para"> Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected. Consider the following code snippet: </p> <p class="para"> <div class="example"> <p><b>Example #5 Incorrect usage of default function arguments</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">makeyogurt</span><span style="color: #007700">(</span><span style="color: #0000BB">$type </span><span style="color: #007700">= </span><span style="color: #DD0000">"acidophilus"</span><span style="color: #007700">, </span><span style="color: #0000BB">$flavour</span><span style="color: #007700">)<br />{<br /> return </span><span style="color: #DD0000">"Making a bowl of $type $flavour.\n"</span><span style="color: #007700">;<br />}<br /> <br />echo </span><span style="color: #0000BB">makeyogurt</span><span style="color: #007700">(</span><span style="color: #DD0000">"raspberry"</span><span style="color: #007700">); </span><span style="color: #FF8000">// won't work as expected<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> The output of the above example is: </p> <p class="para"> <div class="example-contents"><pre>Warning: Missing argument 2 in call to makeyogurt() in /usr/local/etc/httpd/htdocs/phptest/functest.html on line 41Making a bowl of raspberry . </pre></div> </p> <p class="para"> Now, compare the above with this: </p> <p class="para"> <div class="example"> <p><b>Example #6 Correct usage of default function arguments</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">makeyogurt</span><span style="color: #007700">(</span><span style="color: #0000BB">$flavour</span><span style="color: #007700">, </span><span style="color: #0000BB">$type </span><span style="color: #007700">= </span><span style="color: #DD0000">"acidophilus"</span><span style="color: #007700">)<br />{<br /> return </span><span style="color: #DD0000">"Making a bowl of $type $flavour.\n"</span><span style="color: #007700">;<br />}<br /> <br />echo </span><span style="color: #0000BB">makeyogurt</span><span style="color: #007700">(</span><span style="color: #DD0000">"raspberry"</span><span style="color: #007700">); </span><span style="color: #FF8000">// works as expected<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> The output of this example is: </p> <p class="para"> <div class="example-contents"><pre>Making a bowl of acidophilus raspberry. </pre></div> </p> <blockquote><p><b class="note">Note</b>: <span class="simpara"> As of PHP 5, default values may be passed by reference. </span> </p></blockquote> </div> <div id="functions.variable-arg-list" class="sect2"> <h3 class="title">Variable-length argument lists</h3> <p class="simpara"> PHP 4 and above has support for variable-length argument lists in user-defined functions. This is really quite easy, using the <a href="function.func-num-args.html" class="function">func_num_args()</a>, <a href="function.func-get-arg.html" class="function">func_get_arg()</a>, and <a href="function.func-get-args.html" class="function">func_get_args()</a> functions. </p> <p class="simpara"> No special syntax is required, and argument lists may still be explicitly provided with function definitions and will behave as normal. </p> </div> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.functions.html">Functions</a></div> <div class="next" style="text-align: right; float: right;"><a href="functions.returning-values.html">Returning values</a></div> <div class="up"><a href="language.functions.html">Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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