php function_exists function problem, repeatedly defining functions

<code>$a=get(1);  //出错,找不到定义
echo $a;
if(!function_exists("get")){
   function get($a){
      return "test";
   }
}</code>

If you want to realize the function, you need to check whether the function is defined. If it is, it will not be defined. If not, just define it.
The function_exists position is at the end of the file, and it will prompt that the function definition cannot be found

Reply content:

<code>$a=get(1);  //出错,找不到定义
echo $a;
if(!function_exists("get")){
   function get($a){
      return "test";
   }
}</code>

If you want to realize the function, you need to check whether the function is defined. If it is, it will not be defined. If not, just define it.
The function_exists position is at the end of the file, and it will prompt that the function definition cannot be found

<code class="php">if(!function_exists("get")){
   function get($a){
      return "test";
   }
}
$a=get(1); // 这不就找到了
echo $a;</code>

Recommended methodis_callable, manual

Explanation of sequential execution..