Summary of various printout functions in php

Development must require debugging code, and PHP debugging code cannot be single-step debugged through development software such as Xcode like the iOS compiler language. Therefore, PHP developers usually print relevant prompts through output functions. information to debug the code.

A step-by-step explanation of commonly used print output functions in PHP

echo

The echo function can output at the same time Multiple strings, with multiple parameters, but parentheses are not required and there is no return value. However, there is no problem if you bring parentheses, so the function requires parentheses:

echo &#39;技术博客<br>&#39;;
echo (&#39;echo也可以带括号<br>&#39;);

I believe the echo function is the most commonly used printing function!

print

The print function can only output one string at a time, can only take one parameter, requires parentheses and will have a return value. Returns false when its execution fails.

print(&#39;www.php.cn<br>&#39;);

The print function is also used quite a lot, for printing information, but it is not as convenient as echo, but it has its uses!

printf

The printf function takes two parameters. The first parameter specifies the output format, and the second parameter is the variable to be output. The output format is:

%s: by string;
%d: by integer;
%b: by binary;
%x: by hexadecimal;
%o: By octal;
$f: By floating point

/*
$var = 10;
printf(&#39;整型：%d<br>&#39;, $var);
printf(&#39;浮点型：%.2f<br>&#39;, $var); // 保留两位小数
printf(&#39;字符串：%s<br>&#39;, $var);
printf(&#39;二进制：%b<br>&#39;, $var);
printf(&#39;八进制：%o<br>&#39;, $var);
printf(&#39;十六进制：%x<br>&#39;, $var);
 
// 打印结果
/*
整型：10
浮点型：10.00
字符串：10
二进制：1010
八进制：12
十六进制：a
*/

#sprintf

sprintf cannot directly output variables value, but directly read the value to the specified variable:

$ret = sprintf('%.2f', $var);
echo "结果：{$ret}<br>";

This function is used to format variable output is very useful and used a lot!

print_r

print_r This function is used to output an array, with one or two. If parameter two is set to YES, the expression information will not be output, but will be returned directly:

##mixed print_r ( mixed $expression [, bool $ return = false ] )

$arr = array('name' => '技术博客', 'site' => 'www.php.cn');
print_r($arr);
echo &#39;<br>&#39;;
 
// 参数二设置为true则不会打印，而是直接返回
$arr1 = print_r($arr, true);
echo "{$arr1}<br>";

var_dump
##var_dump This function is used the most during debugging. It is used to output the contents of variables. The content of type and string is often used for debugging in development:

// 当打印的是字符串，其中有对象时，打印出来是：
// string(20) "var_dump：Array
var_dump(&#39;var_dump：&#39; . $arr . &#39;<br>&#39;);
 
// 当只有对象本身时，打印出来如下：
// " array(2) { ["name"]=> string(21) "技术博客" ["site"]=> string(19) "www.php.cn" }
var_dump($arr);

die

die function is also widely used. During the debugging process, The following execution is often interrupted. It will output the content first, and then exit the program or not output the content:

if (!isset($type)) {
 die(&#39;I am die!<br>&#39;);
}

Summary:

The above functions can print the value of the object , system function values ​​and the contents of arrays;

echo, print, and printf can print variable contents, but cannot display arrays and system super variable arrays;

print_r and var_dump can not only print arrays, scalar variables, but also objects The content;
The var_dump statement can not only print the contents of variables and arrays, but also display the contents of Boolean variables and resources (
resource
); The var_export function returns the structure of the variables passed to the function Information, similar to the var_dump() function, except that the content returned is legal php code
.

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