Internal function means that a function is declared inside the function.

Notes:

1. The internal function name cannot be an existing function name

2. Assume that an internal function is defined in function a, You cannot use function a twice.

Let’s look at the code below, you will learn it quickly:

<?php
function foo()
{
   echo '我是函數(shù)foo喲，調一下我才會執(zhí)行定義函數(shù)bar的過程<br />';
 function bar()
 {
      echo '在foo函數(shù)內(nèi)部有個函數(shù)叫bar函數(shù)<br />';
 }


}

//現(xiàn)在還不能調用bar()函數(shù)，因為它還不存在
bar();

foo();

//現(xiàn)在可以調用bar()函數(shù)了，因為foo()函數(shù)的執(zhí)行使得bar()函數(shù)變?yōu)橐讯x的函數(shù)

bar();

//再調一次foo()看看是不是會報錯？
foo();

?>

You will find that a bar function is defined inside the foo() function above, which is the inner function number .

After careful observation and experimentation, you will draw the following conclusions:

1. Calling foo() twice will report an error

2. If you do not adjust the foo() function The bar function cannot be executed because bar is inside foo