Common causes and solutions for PHP blank pages

Compiling PHP will inevitably lead to errors. In fact, it is not difficult to solve the problem. The most difficult solution is to have a blank page. Let's think about it. If an error occurs when you write PHP, you can correct it according to the error prompt. If PHP does not show you anything, isn't it difficult for the author? Next, I will summarize the solutions and causes for the blank pages of PHP when writing PHP. Of course, I am not very good at writing PHP, so if there is an error, please do not hesitate to point it out.

1. The action is not defined.
Let's take a look at the following code:
[Code]
<? Php
$ Action = $ _ GET ['id'];
If ($ action = '')
$ Action = 1;
If ($ action = 1 ){
Echo ("$ action's value is 1 ");
} Else if ($ action = 2 ){
Echo ("$ action's value is 2 ");
}
?>
[/Code]
You can understand this code, that is, if the $ action variable is empty, set it to 1, and then determine the value of the $ action variable to make different events. Of course, what will PHP do if $ action is neither 1 nor 2 ??