What are the commonly used methods for printing variables in PHP?

Commonly used methods are: 1. Use echo(), the syntax "echo($var)"; 2. Use var_dump(), the syntax "var_dump($var)"; 3. Use print(); 4 , use print_r(); 5. use printf(); 6. use sprintf().

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

A common way to print variables:

1. echo()

echo outputs one or more strings, which is a PHP statement. It is not a function, so it has no return value

<?php       $name = &#39;张三&#39;; 
   echo($name); 
?>

2、var_dump()

var_dump() Used to display structural information about one or more expressions, print the type, value, and length of the variable

<?php    $name = &#39;张三&#39;; 
  var_dump($name); 
?>

Output result:

3. print()

print() is used to output information about one or more strings or variable values. It can only print out the values ​​of simple type variables, and cannot print arrays and objects (print () is slightly slower than echo())

4. print_r()

print_r() is a function used to print easy-to-understand information about variables.

print_r function prototype: bool print_r (mixed expression [, bool return] )

It can be seen from the above that the return value of print_r is Boolean, and the parameters are of mix type. Can be a string, integer, array, object class print_r() displays easy-to-understand information about a variable. If a string, integer, or float is given, the variable value itself is printed. If an array is given, the keys and elements will be displayed in a certain format. object is similar to an array.

<?php
$a = array (&#39;a&#39; => &#39;apple&#39;, &#39;b&#39; => &#39;banana&#39;, &#39;c&#39; => array (&#39;x&#39;,&#39;y&#39;,&#39;z&#39;));
print_r ($a);
?>

5. printf()

Function printf() is used to output formatted strings, and C language The functions with the same name are used the same way. The syntax format of the function is as follows:

printf(string $format[, mixed $args[, mixed $... ]])

Among them, $format is a required parameter, which is used to set the string and how to format the variables in it; the remaining parameters (such as $args) are optional parameters. Used to set the parameters inserted into $format at the corresponding "%" symbol.

The conversion format used by the first parameter of the printf() function is to replace the uncertain (dynamic) part of the string with a placeholder. The placeholder is converted from the percent symbol "%" to Represented by characters, as shown in the table below.

##%E Use uppercase scientific notation (e.g. 1.2E 2) %uUnsigned decimal number%fFloating point number (local setting)%FFloating point number (non-native setting)%g Shorter %e and %f%GShorter %E and %f##%o%s%x%X

占位符的 % 于后面的字母之间也可以插入一些附加的内容（例如 %.2f）：

• +：在数字前面加上 + 或 - 来定义数字的正负性。默认地，只有负数做标记，正数不做标记；

• '：规定使用什么作为填充，默认是空格。它必须与宽度指定器一起使用，例如 %'x20s；

• -：左调整变量值；

• [0-9]：规定变量值的最小宽度；

• .[0-9]：规定小数位数或最大字符串长度；

注意：如果使用多个上述的格式值，它们必须按照上面的顺序进行使用，不能打乱。

【示例】使用 printf() 函数输出指定的字符串。

<?php
$number = 9;
$str = "北京";
printf("在%s有 %u 百万辆自行车。",$str,$number);
?>

6、sprintf()

sprintf() 函数的用法和 printf() 相似，但它并不输出字符串，而是把格式化后的字符串以返回值的形式返回，我们可以使用一个变量来接收 sprintf() 函数的返回值，这样就可以在需要时侯使用这个格式化后的字符串了。示例代码如下所示：

<?php
    $num = 3.1415926;
    $str = sprintf(&#39;%.2f&#39;, $num);
    echo $str;
?>

运行结果如下：

3.14

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Format	Function Description
%%	Return the percent symbol
%b	Binary number
%c	Character corresponding to the ASCII value
%d	Decimal numbers containing signs (negative numbers, 0, positive numbers)
%e	Use lowercase scientific notation method (e.g. 1.5e 3)
Octal number
String
Hexadecimal number (lowercase letters)
Hexadecimal number (uppercase letters)

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