In php, what is the difference between strings surrounded by single quotes and double quotes?

In PHP, there are differences between single quotes and double quotes in string representation: variable interpolation: Single quotes do not perform variable interpolation, while double quotes do. Special escape characters: Single quotes are not supported, double quotes are supported. String concatenation: Single quotes only concatenate when adjacent, double quotes always concatenate.

The difference between single quotes and double quotes in PHP

In PHP, strings can be represented by single quotes or enclosed in double quotes. There are some key differences in syntax between these two quote types:

1. Variable interpolation

• Single quotes: will not work String for variable interpolation. This means that any variable enclosed in single quotes will be output unchanged without being replaced by its value.
• Double quotes: will perform variable interpolation on the string. If the string in double quotes contains a variable, the variable will be replaced by its value.

For example:

<code class="php">$name = "John Doe";
echo 'My name is $name.'; // 输出：My name is $name.
echo "My name is $name."; // 输出：My name is John Doe.</code>

2. Special escape characters

• Single quote : Special escape characters (for example, \n, \t) are not supported.
• Double quotes: supports special escape characters, which are used to represent special characters such as newlines and tabs.

For example:

<code class="php">echo 'This is a new line: \n'; // 输出：This is a new line: \n
echo "This is a new line: \n"; // 输出：This is a new line: <换行></code>

3. String concatenation

• Single quotes: String concatenation is performed only when two single-quoted strings are adjacent.
• Double quotes: Always perform string concatenation, even if there are spaces between strings.

For example:

<code class="php">$firstName = 'John';
$lastName = 'Doe';
echo $firstName' '$lastName; // 输出：John $lastName
echo $firstName." ".$lastName; // 输出：John Doe</code>

Summary

In general, single quotes are used for characters that need to be output as is string or does not support special escape characters. Double quotes are used when variable interpolation is required or when special escape characters are used.

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