PHP four ways to define strings

This article mainly introduces the PHP definition string of four ways, has a certain reference value, now share to everyone, the need for friends can refer to

1. Single quotation mark

In single quotes, any special characters are output as-is "except \ \ and \ ' will be escaped output" only single quotes, backslashes are escaped

2, double quotes

The difference between single and double quotes

Double quotation marks replace the value of a variable, and single quotes treat it as a string output.

Support for escaping

Performance speed problem, because the string in double quotes needs to detect whether a variable containing the $ symbol decoration, in theory, the single quotation mark is relatively fast (single quotation mark efficiency is higher)

3, Heredoc

Heredoc can be understood not to use double quotes to define strings, but the effect is consistent with using double quotes. "Double quotation marks are equivalent to ordinary characters" (Long string)

Syntax requirements:

1, opening and closing tags use the same string, usually written in uppercase letters.

2. No spaces or extra characters can appear after the start tag.

3. The closing tag must be written on the head, not indented and blank, and there should be a semicolon at the end of the tag.

4. Variables located between the opening and closing tags can be parsed normally, but the function is not allowed.

The double quotation marks are just one ordinary character, and the other effect is consistent with the string effect of the double quotation marks.

Cases:

<?php$var = ' This is Suifeng '; Echo <<< "Eto" $var <br/> "666666" Eto

Output:

This is Suifeng

666666

4,Nowdoc

Similarly, Nowdoc is defined without using single quotes, but the effect is equivalent to a string defined using single quotation marks. "The single quotation marks are equivalent to ordinary characters at this time"

Data type

Three big data types "scalar, compliant, special"

Floating-point types

Floating-point types cannot be applied to comparison operators

Boolean type

Seven cases of false

Integer 0, floating point 0.0, Boolean false, empty string, 0 string, empty array, NULL

Array type

Hyper-Global Array

• $GLOBALS

• $_server

• $_request

• $_post

• $_get

• $_files

• $_env

• $_cookie

• $_session

Null three cases

Variables that are directly assigned null, undefined variables, unset () destroyed

Constant

Defined

Const define

Const faster, is the language structure, define is the function

Define cannot be used for definition of class constants, const can, constants cannot be modified once defined, cannot be deleted

Predefined Constants (Magic constants)

• __line__ : Returns the current line number in the file. Can also be written as __line__.

• __file__: Returns the absolute path (including the file name) of the current file.

• __dir__: Returns the absolute path (without the file name) of the current file, equivalent to dirname (__file__).

• __function__: Returns the name of the current function (or method).

• __class__: Returns the current class name (including the scope or namespace of the class).

• __trait__: Returns the current TRAIT name (including the scope or namespace of the TRAIT).

• __method__: Returns the current method name (including the class name).

• __namespace__: Returns the name of the namespace for the current file.