PHP 中的 Print_r()-php教程-PHP中文網

PHP 中的 Print_r()

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發布： 2024-08-29 12:52:14

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PHP 開發人員使用 print_r() 函數產生有關腳本中變數的人類可讀資訊。他們可以將函數的輸出儲存在變數中或直接在輸出視窗上列印。儲存或顯示值的行為取決於提供給函數的輸入參數。要注意的是，從 PHP 版本 4 開始就支援 print_r()，包括 PHP4、PHP5 和 PHP7。

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文法:

您可以使用以下語法在任何 PHP 腳本中實作 print_r() 函數：

print_r ( mixed $variable_name , bool $returnType) : mixed

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variable_name 參數的值是必要的，而 $returnType 是可選的。

PHP中print_r()的參數

此方法可接受兩個參數作為輸入參數。

1. $變數_名稱

此參數是 print_r() 方法的強制輸入參數。它指定函數需要以人類可讀的格式提取資訊的變數。對於類別變量，此方法還捕獲類別成員的屬性。

2. $returnType

此函數有一個可選的輸入參數，可讓您決定是否儲存或列印輸出。您可以使用此參數來確定所需的行為。

這是一個布林類型的參數。此參數的預設值設定為FALSE。

Value of ReturnType	Description
TRUE	The function provides a return value that you can store in a variable.
FALSE	The function prints the output; you cannot capture or store the value.

ReturnType 的值描述 TRUE 函數提供一個傳回值，您可以將其儲存在變數中。 FALSE 函數列印輸出；您無法捕獲或儲存該值。表>

Return Value:

The return value of the function depends on the type of the variable and the value of the returnType as the input argument. If a given variable is of type string, integer, or float, the return value is the variable itself as it is. When you set the return type to FALSE, and the input variable is an array or object, the function will return the keys and elements as the output values.

When the returnType is set to TRUE, print_r() results in a storable outcome.

Note: By default, the value for returnType is FALSE. Thus the default functionality of the print_r() method is the print/display the information of the given variable. To configure the function to capture the output and store it in different variables, the developer needs to use the parameter returnType in its print_r() function call by setting the value to TRUE.

Examples to Implement of print_r() in PHP

Below are the examples of print_r() in PHP:

Example #1

The code snippet below illustrates the functionality of print_r() in displaying information about a string variable, an integer variable, and an array input. To achieve this, you must include only the input variable as a parameter in the function call. In this case, the default value of the returnType parameter is FALSE.

Code:

<?php
// PHP program to illustrate the print_r() function to exhibit printing functionality :
// Declaring a string variable
$input_str = "An information string";
// Declaring a  integer variable
$input_int= 101;
// Declaring an array variable
$input_arr = array("Count1"=>"35", "Count2"=>"45", "Count3"=>"55");
// printing the variables
print_r("Printing the string variable information");
echo"\n";
print_r($input_str);
echo"\n";
echo"\n";
print_r("Printing the integer variable information");
echo"\n";
print_r($input_int);
echo"\n";
echo"\n";
print_r("Printing the array variable information");
echo"\n";
print_r($input_arr);
?>

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Output:

PHP 中的 Print_r()

As mentioned earlier, when handling string and integer variables, the information is printed as it is. However, when it comes to an array variable, the output displays the data in the format of key-value pairs and their corresponding data types.

Example #2

By default, the value is FALSE. To capture and store the output from print_r() in a variable, you need to set the returnType parameter as TRUE in the function call.

Code:

<?php
// PHP program to illustrate the print_r() function exhibiting the storing functionality
// Declaring a string variable
$input_str = "An information string";
// Declaring an integer variable
$input_int= 5040;
// Declaring an array variable
$input_arr = array("element1"=>"31", "element2"=>"41", "element3"=>"51");
// Capturing and storing the output in different variables
print_r("Capturing the integer variable information");
echo"\n";
//Storing the integer variable output
$input_int_cap=print_r($input_int,true);
print_r($input_int_cap);
echo"\n";
echo"\n";
print_r("Capturing the string variable information");
echo"\n";
//Storing the string variable output
$input_str_cap=print_r($input_str,true);
print_r($input_str_cap);
echo"\n";
echo"\n";
print_r("Capturing the array variable information");
echo"\n";
//Storing the array variable output
$input_arr_cap=print_r($input_arr,true);
print_r($input_arr_cap);
?>

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Output:

PHP 中的 Print_r()

Variables of their respective data types capture and store the information from integer and string variables. On the other hand, when dealing with an array variable, the function stores the output in a dedicated variable specifically designed to hold arrays. This storage encompasses the key-value pairs and the associated data types of each element.

The display result refers to the output produced using print_r() with storing variables.

Additional Note

This method can also show properties of private and protected properties of an object, whereas it has restricted features that will not show results for static class members.
In PHP 5, you can utilize the Reflection class to employ print_r() for static class member variables.
Developers commonly use print_r() for debugging PHP scripts.
Using the returnType parameter in the function call of print_r() involves the utilization of internal output buffering. As a result, it is impossible to employ print_r() within an ob_start() callback method.