PHP——Function 2_study notes php rounding function php delay function php sorting function

1. Variable function (variable function)
The value of the variable is the name of a function.
e.g:

<code>```
<span><span>function</span><span>show</span><span>(<span>$a</span>,<span>$b</span>)</span>{</span><span>return</span><span>$a</span>+<span>$b</span>;
}
<span>$str</span>=<span>"show"</span>;
<span>echo</span><span>$str</span>(<span>10</span>,<span>5</span>);
``</code>

2. Callback function
Callback function, the parameter of the function is the name of another function.

<code>```
<span><span>function</span><span>show</span><span>(<span>$a</span>,<span>$b</span>)</span>{</span><span>return</span><span>$a</span>+<span>$b</span>;
}
<span><span>function</span><span>test</span><span>(<span>$i</span>,<span>$j</span>,<span>$k</span>)</span>{</span><span>return</span><span>$k</span>(<span>$i</span>,<span>$j</span>);
}
<span>$num</span>=test(<span>10</span>,<span>5</span>,<span>"show"</span>);
<span>echo</span><span>$num</span>;
``</code>

3. Recursive function
A function calling itself within its function body is called a recursive call (the function calls itself inside the function)

<code><span><span>function</span><span>test</span><span>()</span>{</span><span>static</span><span>$num</span>;
       <span>$num</span>++;
       <span>if</span>(<span>$num</span><=<span>10</span>){
         <span>echo</span><span>'this is num '</span>.<span>$num</span>.<span>'<br>';
         test();<span>//自己再调用自己</span>
       }
    }

    test();</code>

4.function_exits(string $function_name)
Determine whether the function exists, the return value is bool;

<code><span>if</span>(function_exists(<span>'show'</span>)){
        <span>exit</span>(<span>'此函数名称已存在'</span>);
    }<span>else</span>{
        <span><span>function</span><span>show</span><span>()</span>{</span>        }
    }

    var_dump(function_exists(<span>'show'</span>));</code>

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