PHP code audit (1)-----Debugging function

The content of this article is to share with you debugging functions. Friends who are interested can take a look at it, and can also give some reference to students who need help

• The two most basic output methods echo and print

/**
*echo 是一个语言结构，有无括号均可使用：echo 或 echo()
*///打印字符串echo "hello";
echo("hello");//打印变量$text="learn php";
echo $text;
echo($text);

/**
print 也是语言结构，有无括号均可使用：print 或 print()
*///打印字符串print "hello";
print("hello");//打印变量$text="learn php";
print $text;
print($text);

echo The difference between print and print:

echo - can output more than one string
print - can only output one string and always returns 1
Tip: echo is slightly smaller than print Fast because it does not return any value

• The difference between double quotes and single quotes

Double quotes Parsing variables
Single quotes do not parse variables

 $str1="hello"; $str2="php"; echo "$str1";//输出：hello echo '$str2';//输出：$str2

• print_r() function

print_r() displays about Easy-to-understand information about a variable. If a string, integer
, or float is given, the variable value itself will be printed. If an array is given, the keys
and elements will be displayed in a certain format. object is similar to an array.
Remember, print_r() will move the array pointer to the end. Use reset() to return the pointer to the beginning.

//打印string$str1="hello";
print_r($str1);
print_r("hello");//打印integer$num=1024;
print_r($num);
print_r(1024);//打印float$num=1024.1024;
print_r($num);
print_r(1024.1024);//打印array
 $cars=array("Volvo","BMW","Toyota");
 print_r($cars);/*打印结果
Array ( [0] => Volvo [1] => BMW [2] => Toyota )
*/

• *var_dump() function
  var_dump() method, determines the type and length of a variable, and outputs the value of the variable. If the variable has a value, the output is of the variable. value and return data type. for precise debugging.
  Display structural information about one or more expressions, including the type and value of the expression. Arrays will expand values ​​recursively, showing their structure through indentation.

 $cars=array("Volvo","BMW","Toyota");
 var_dump($cars); /* 打印结果
 E:\wamp64\www\test.php:56:
array (size=3)
  0 => string 'Volvo' (length=5)
  1 => string 'BMW' (length=3)
  2 => string 'Toyota' (length=6)
 */


 $n=null;
 var_dump($n); /*打印结果
 E:\wamp64\www\test.php:59:null
 */

• var_export() function
  var_export() function returns structural information about the variable passed to the function, it and var_dump() is similar, except that the representation returned is legal PHP code. var_export must return legal PHP code. In other words, the code returned by var_export can be directly assigned to a variable as PHP code. And this variable will get the same type of value as var_export.

Note three points:
1.var_export() will always retain the structured form to store data.
2.But please remember : The type of the variable value at this time is already a string ($var), and the value can no longer be taken out in the form of an array.
3. var_export will output NULL

 $cars=array("Volvo","BMW","Toyota");
 var_export($cars);
 /*打印结果
 array ( 0 => 'Volvo', 1 => 'BMW', 2 => 'Toyota', )
 */

for resource-type variables.

• debug_zval_dump() function
  debug_zval_dump() The output result is similar to var_dump. The only added value is refcount, which records how many times a variable has been referenced. This is PHP An important feature of the copy on write mechanism.

 $cars=array("Volvo","BMW","Toyota");
 debug_zval_dump($cars);
 /*打印结果  array(3) refcount(2){ [0]=> string(5) "Volvo" refcount(1) [1]=> string(3) "BMW" refcount(1) [2]=> string(6) "Toyota" refcount(1) }
 */

• exit() function
  Terminate the program running

• The two most basic output methods echo and print

/**
*echo 是一个语言结构，有无括号均可使用：echo 或 echo()
*///打印字符串echo "hello";
echo("hello");//打印变量$text="learn php";
echo $text;
echo($text);

/**
print 也是语言结构，有无括号均可使用：print 或 print()
*///打印字符串print "hello";
print("hello");//打印变量$text="learn php";
print $text;
print($text);

The difference between echo and print:

echo - can output more than one string
print - can only output one string and always returns 1
Tip: echo is slightly faster than print because it does not return any value

• The difference between double quotes and single quotes

Double quotes parse variables
Single quotes do not parse variables

 $str1="hello"; $str2="php"; echo "$str1";//输出：hello echo '$str2';//输出：$str2

• print_r() Function

print_r() Displays easy-to-understand information about a variable. If a string, integer
, or float is given, the variable value itself will be printed. If an array is given, the keys
and elements will be displayed in a certain format. object is similar to an array.
Remember, print_r() will move the array pointer to the end. Use reset() to return the pointer to the beginning.

//打印string$str1="hello";
print_r($str1);
print_r("hello");//打印integer$num=1024;
print_r($num);
print_r(1024);//打印float$num=1024.1024;
print_r($num);
print_r(1024.1024);//打印array
 $cars=array("Volvo","BMW","Toyota");
 print_r($cars);/*打印结果
Array ( [0] => Volvo [1] => BMW [2] => Toyota )
*/

• *var_dump() function
  var_dump() method, determines the type and length of a variable, and outputs the value of the variable. If the variable has a value, the output is of the variable. value and return data type. for precise debugging.
  Display structural information about one or more expressions, including the type and value of the expression. Arrays will expand values ​​recursively, showing their structure through indentation.

 $cars=array("Volvo","BMW","Toyota");
 var_dump($cars); /* 打印结果
 E:\wamp64\www\test.php:56:
array (size=3)
  0 => string 'Volvo' (length=5)
  1 => string 'BMW' (length=3)
  2 => string 'Toyota' (length=6)
 */


 $n=null;
 var_dump($n); /*打印结果
 E:\wamp64\www\test.php:59:null
 */

• var_export() function
  var_export() function returns structural information about the variable passed to the function, it and var_dump() is similar, except that the representation it returns is legal PHP code. var_export must return legal PHP code. In other words, the code returned by var_export can be directly assigned to a variable as PHP code. And this variable will get the same type of value as var_export.

Note three points:
1.var_export() will always retain the structured form to store data.
2.But please remember : The type of variable value at this time is already a string ($var), and the value inside can no longer be taken out in the form of an array.
3. var_export will output NULL

 $cars=array("Volvo","BMW","Toyota");
 var_export($cars);
 /*打印结果
 array ( 0 => 'Volvo', 1 => 'BMW', 2 => 'Toyota', )
 */

• debug_zval_dump（）函数
  debug_zval_dump（） 输出结果跟 var_dump 类似，唯一增加的一个值是 refcount，就是记录一个变量被引用了多少次，这是 php 的 copy on write (写时复制) 的机制的一个重要特点。

 $cars=array("Volvo","BMW","Toyota");
 debug_zval_dump($cars);
 /*打印结果  array(3) refcount(2){ [0]=> string(5) "Volvo" refcount(1) [1]=> string(3) "BMW" refcount(1) [2]=> string(6) "Toyota" refcount(1) }
 */

• exit()函数
  终止程序运行

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