What is the difference between foo() and @foo() in php

The difference between "foo()" and "@foo()" in php: "@foo()" is the error control output, all errors will be ignored, "foo()" is the normal call output . "@" is the error suppressor. When placed before a PHP expression, all error reports for the expression will be ignored.

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

Operation The difference between Foo() and @foo() is that

@foo() is the error control output, and foo() is the normal call output.

@ is an error suppressor; when placed before a PHP expression, all errors in the expression will be ignored; the

@ symbol can ignore error reports in PHP, for expressions Some prompt errors, but some do not affect statement execution. You can add @ before the expression.

You can put the @ symbol before variables, functions, include() calls, constants, etc., but you cannot put @ before the definition of functions and classes, nor can it be used before conditional structure statements

eg: if, switch, while, for and foreach, etc.

Extension: All PHP operator test points

1) PHP operator precedence (from high to low)

• increment/decrement
• !
• arithmetic operator
• Size comparison
• (Not)Equality comparison
• Quote
• Bit operator (^)
• Bit operator (|)
• Logic and
• Logic or
• 三目
• Assignment
• and
• xor
• or

Note: The use of brackets can increase the readability of the code. It is recommended to use

2) Compare Operator: The difference between == and ===

• == Comparison value is equal; === Comparison value Whether they are equal and whether their types are the same.
• Equal value judgment (seven cases of FALSE)
  if ('== false') {
  echo '';
  } elseif ('0' == 0 ) {
  echo '';
  } elseif (0.0 == 0) {
  echo '';
  }

Note:

• All seven cases of FALSE are satisfied:
  • Integer type 0
  • Floating point type 0.0
  • Zero string '0'
  • Empty string'' "
  • Empty array array()
  • null
  • Boolean false

3) Increment/decrement operator

• The increment/decrement operator does not affect Boolean values;
  • true ; // true
  • true–; // true
  • false ; // false
  • false–; // false
• Decrementing the NULL value has no effect; incrementing the NULL value is 1;
  • NULL–; // NULL
  • #NULL; // 1
• If increment and decrement come first, they will be operated first and then returned; otherwise, they will be returned first and then operated

4) Logical operators

① Short circuit effect

$a = true || $b == 3; // 前面是 true，后面不会执行【|| : 一真为真】
$b = false && $a == 1; // 前面是 false，后面不会执行【&&：一假为假】

② || and && have different priorities than or and and

// 先执行 false || true，得到 true,再赋值给 $a
$a = false || true; // $a = true;

// 先执行 $b = false，整体为 true，则 $b的值为 false
$b = false or true; // $b = false；

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