PHP used ', ' and '. ' The difference

PHP used ', ' and '. ' The difference

$str 1 = ' Hello ';

$str 2 = ';

$str 3 = ' world ';

$str = $str 1. $str 2. $str 3;

Echo $str, '

‘; Hello world;

Novice questions, even six months of work also doubt.

How can I use ', '

echo $str 1, $str 2, $str 3, '

‘; Hello World

echo $str 1. $str 2. $str 3. ‘

‘; Hello World

/*

This line, is $STR1, $str 2, $str 3 in memory, stitching,

To compute a big string of ' Hello World ',

And then echo, get the result of the judgment.

echo $str 1. $str 2. $str 3. ‘

‘; Hello World

echo $str 1, $str 2, $str 3, '

‘; Hello World

Echo is a statement that is responsible for the output,

You can output multiple variables or values at once by ', ' split.

Comprehensive:

With '. ' Is stitching first, then the entire output.

Using ', ' is asked to output 3 variables.

Interview, you will encounter this question:

The above two situations, with ', ' and with '. ' Which output is fast, high efficiency?

A: The comma is fast because it eliminates the process of a concatenation calculation.