PHP：如何避免重新声明函数？
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PHP: how to avoid redeclaring functions?
提问by hhh
I tend to get errors such as:
我倾向于得到错误，例如：
Fatal error: Cannot redeclare get_raw_data_list() (previously declared in /var/www/codes/handlers/make_a_thread/get_raw_data_list.php:7) in /var/www/codes/handlers/make_a_thread/get_raw_data_list.php on line 19
致命错误：无法在第 19 行的 /var/www/codes/handlers/make_a_thread/get_raw_data_list.php 中重新声明 get_raw_data_list()（之前在 /var/www/codes/handlers/make_a_thread/get_raw_data_list.php:7 中声明）
how can I avoid the error? Is it possible to create a IF-clause to check whether a function is declared before declaring it?
我怎样才能避免这个错误？是否可以创建一个 IF 子句来在声明之前检查函数是否已声明？
采纳答案by karim79
Use require_onceor include_onceas opposed to includeor requirewhen including the files that contain your functions.
使用require_once或include_once与包含包含您的函数的文件相反的include或require。
The _oncesiblings of includeand requirewill force PHP to check if the file has already been included/required, and if so, not include/requireit again, thereby preventing 'cannot redeclare x function...' fatal errors.
本_once的兄弟姐妹include和require将强制PHP检查文件是否已被列入/必需的，如果是这样，不是include/require一遍，从而防止“无法重新声明X功能...”致命错误。
回答by Dooltaz
if(!function_exists("get_raw_data_list")) {
... define function here ...
}
回答by smack0007
"function_exists" will tell you if a function has already been declared. Though I suspect maybe you have a problem with including files more than once. When you include a file are you using require_once or include_once or just require / include?
“ function_exists”会告诉你一个函数是否已经被声明。尽管我怀疑您可能在多次包含文件时遇到问题。当您包含文件时，您是使用 require_once 或 include_once 还是只使用 require / include？
回答by Serj Sagan
If you are dealing with Classes method_exists()might be what you're looking for:
如果您正在处理类method_exists()可能是您正在寻找的：
if(!method_exists(__CLASS__, 'function_name')){
function function_name(){
}
}
This will check the current Class to make that the function function_namedoesn't exist before trying to declare it
这将function_name在尝试声明之前检查当前类以确保该函数不存在
