PHP language constructor introduction _ PHP Tutorial

Introduction to the PHP language constructor. PHP contains several special keywords, such as echo, print, die, and require. although they are used as functions, they are actually similar to control statements like if and while, rather than a function. PHP contains several special keywords, such as echo, print, die, and require. although they are used as functions, they are actually similar to control statements like if and while, rather than a function. That is, when the interpreter encounters:

The code is as follows:

Print 'Hello World ';

In such an expression, it is not converted into a function call, but directly mapped to a series of pre-defined operations. When using a language, you can add parentheses or do not add parentheses, but you must add parentheses when using a function.

The variable function you mentioned is variable function. translating it into a variable function is also a little distorted) the term is translated according to the meaning of the adjective (variable. The Variable function in PHP is a function with the same name and value as the Variable if a pair of parentheses is added to the Variable. if the Variable is found, the interpreter tries to execute it. For example, if there is a function foo (), you can use the following method to call this function:

The code is as follows:

// Initialize a string variable
$ Func = 'foo ';

// Find the function with the same name as this string and execute it
$ Func ();

Therefore, the meaning of the sentence you mentioned is that using a variable function to call a language is not allowed. for example:

The code is as follows:

$ Func = 'print ';

// This will cause an exception because print is not a function but a component of the language.
$ Func ('Hello World ');

When this code is executed, an exception occurs, and the print function is not defined.

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