What is the usage of curly braces in php

There are many ways to use php curly braces, such as: 1. "function name(){}" or "for(){}" usage; 2. "$str{4}" usage; 3. "{$val}" usage.

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

# What is it?

Detailed explanation of the use of PHP braces (curly braces {})

1. No matter what program, function name(){}, for(){ }, ....This is too much, and I don’t even know what it is used for.

2. $str{4} is followed by

{}

after the variable of the string. Braces and square brackets

[]

both replace a certain character. String variables are treated as arrays.

3. {$val} is the problem I encountered. At this time, the role of the curly brackets is to tell PHP that the enclosed items should be treated as variables. The following example:

//The following is okay as it's inside a string. Constants are not
//looked for within strings so no E_NOTICE error here
print "Hello $arr[fruit]"; // Hello apple

//With one exception, braces surrounding arrays within strings
//allows constants to be looked for
print "Hello {$arr[fruit]}"; // Hello carrot
print "Hello {$arr['fruit']}"; // Hello apple

######Another: The role of braces (braces {}) in PHP string variables#########Add after the PHP variable A curly bracket {}, filled with numbers, refers to the characters of the corresponding serial number of the PHP variable. ######For example: ######$str = 'hello';###

echo $str{0}; // 输出为 h ,也可以 $str[0]
echo $str{1}; // 输出为 e ,也可以 $str[1]

###If you want to check whether a string meets a certain length, you can consider using this kind of braces (curly braces ) to replace the strlen function by adding isset. Because isset is a language structure and strlen is a function, using isset is more efficient than using strlen. ######For example, to determine whether the length of a string is less than 5: ######if (!isset ($str{5})) is better than if (strlen ($str)

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