The difference between using commas and dots to connect echo in PHP programming_php skills

It is mentioned that using echo string is better than using .connection. Let’s not talk about the reasons first, let’s look at the following two sentences

 <&#63;php
 // 逗号比.更节省时间&#63;
 echo '1+5=' . 1+5; 
 echo '1+5=' . 5+1;

What is the result?

1+5=6？
1+5=6？
——————
6？
2？
——————
6.6？
6.6？
——————

I can only say that the result of echo '5 1=' . 1 5; is 10, so the results are 6 and 2.

Why is this? Is there no commutative property in addition in PHP? Of course not..
Let’s not think about why. If I replace the period above with a comma, try it.

echo '1+5=' , 5+1;  //输出 1+5=6 
echo '1+5=' , 1+5;  //输出 1+5=6 

It can be seen that only by using commas can we get the expected results.

Then why doesn’t a period work? Why does a comma work?

echo ('1+5' . 5)+1; //输出2 

After adding parentheses to the previous one, the result will be the same.

Prove that PHP first concatenates strings and then performs addition calculations. It proceeds from left to right.

That’s great. Since the string is connected first, it should be "1 55". Then add 1 to this string. Then why is 2 output?

This is related to the mechanism of converting strings into numbers in PHP. Let’s look at the following example

echo (int)'abc1';  //输出0
echo (int)'1abc'; //输出1
echo (int)'2abc'; //输出2
echo (int)'22abc'; //输出22

We can see from the above example that if a string is forced to be converted into a number, PHP will search for the beginning of the string. If the beginning is a number, it will be converted.

If not, just return 0.

Go back to the 1 55 just now. Since this string is 1 55, it should be 1 after forced type conversion. Add 1 to this. Of course it is 2.
In order to prove our conjecture, let’s verify it.

echo '5+1=' . 1+5; //输出10
echo '5+1=' . 5+1; //输出6
echo '1+5=' . 1+5; //输出6
echo '1+5=' . 5+1; //输出2

The results proved that our assumption was correct.
So why does using commas avoid the above problems?

The manual says that using commas means multiple parameters.

That is to say, it is multi-parameter. In other words.

Comma separated is equivalent to N parameters. In other words, echo is used as a function.

In this case, echo will calculate each parameter first and then connect it and output it. So if we use commas, the above problem will not exist :)

php echo manual

<&#63;php
// Strings can either be passed individually as multiple arguments or
// concatenated together and passed as a single argument
echo 'This ', 'string ', 'was ', 'made ', 'with multiple parameters.', chr(10);
echo 'This ' . 'string ' . 'was ' . 'made ' . 'with concatenation.' . "\n";

As for why it is fast, it can be easily understood. Use . to splice it into echo first, although the number of commas represents the number of echo calls (it can be understood this way for now).
But the splicing speed is slower than the echo speed.
If you understand it deeply, VLD is as shown below. It’s a picture of @tywei the great god

There is one more CONCAT on the top than on the bottom, and one more echo on the bottom than on the top.