Methods for passing parameters by PHP functions: 1. Pass by value, copy the value of the actual parameter and then pass it to the formal parameter of the function; 2. Pass by reference, copy the memory address of the actual parameter and pass it For formal parameters of the function; 3. Default parameters, specify a default value for one or more formal parameters of the function; 4. Variable length parameters, which will be passed to the function as an array.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

When calling a function, you need to pass parameters to the function , the parameters passed into the function are called actual parameters, and the parameters defined by the function are called formal parameters. There are four ways to pass parameters to a function, namely passing by value, passing by reference, default parameters and variable length parameters.

1. Value passing

Value passing is the default value passing method for functions in PHP, also known as "copy passing by value". As the name suggests, the value passing method will copy the value of the actual parameter and then pass it to the formal parameter of the function, so operating the value of the parameter in the function will not affect the actual parameters outside the function. Therefore, if you do not want the function to modify the value of the actual parameter, you can pass it by value.

[Example] The following defines a simple function. The function has two parameters, and the values ​​of the parameters are exchanged in the function.

The running results are as follows:

It can be seen from the running results that the values ​​​​are indeed exchanged within the function, but outside the function, the values ​​​​do not change. So we can say that passing a function by value is just passing a copy of the variable. So if you want the function to be able to operate on external parameters of the function, you need to use reference passing.

2. Passing by reference

Passing by reference is to copy the memory address of the actual parameter and then pass it to the formal parameter, actual parameter and formal parameter of the function. They all point to the same memory address, so the function's operation on the formal parameters will affect the actual parameters outside the function.

Passing by reference is to pass the memory address of the actual parameter to the formal parameter of the function. Therefore, the actual parameters and formal parameters point to the same memory address. At this time, all operations inside the function will affect the values ​​of the actual parameters outside the function. The method of passing by reference is to add an & symbol on the basis of value passing, as shown below:

[Example] Slightly adjust the code of the above example and use the method of passing by reference to pass to the swap function. Parameters, the code is as follows:

The running result is as follows:

3. Default parameters

The default parameter is a certain or Multiple formal parameters specify a default value. If the corresponding value is not passed in when calling the function, the function will use this default value. This can avoid errors when calling without parameters, and can also make some programs more reasonable. If the corresponding parameters are passed in, this default value will be replaced.

The default parameters of the function are as follows:

Among them, the "PHP Chinese Network" after the formal parameter $str is its default value, and the = connection needs to be used between the formal parameters and the default values. .

[Example] Let’s define a function with default parameters as follows:

The running result is as follows:

The default parameters can also be multiple, and The default parameter must be placed to the right of the non-default parameter, and the value of the specified default parameter must be a specific value, such as a number or a string, rather than a variable.

[Example] Let’s define a function with multiple default parameters as follows:

The running result is as follows:

4. Variable Length parameter

In PHP 5.6 and later versions, the formal parameters of the function can use... to indicate that the function can accept a variable number of parameters, and the variable parameters will be passed as an array Give function. An example is as follows:

The running results are as follows:

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