A brief analysis of the difference between == and === in php

In PHP, sometimes we need to compare whether two variables are equal. In order to achieve this function, we can use the equal operator "==" or the congruent operator "===". Although both operators can perform equality comparisons, there are some differences between them.

In this article, we will introduce the specific functions of "==" and "===" respectively, and discuss their differences and usage scenarios in detail.

1. "==" operator

The "==" operator is the equal operator in PHP, which is used to compare whether the values ​​of two variables are equal. For example:

$x = 4;
$y = "4";
if ($x == $y) {
   echo "变量x和y的值相等";
}

In the above example, although $x and $y have different types, their values ​​are equal. Therefore, using the "==" operator determines that the result is true and outputs "the values ​​of variables x and y are equal."

However, it should be noted that the "==" operator only compares values, regardless of the data type of the variable. Therefore, it is possible that some comparison results may not meet expectations.

For example, in the following example:

$x = 0;
$y = "abc";
if ($x == $y) {
   echo "变量x和y的值相等";
}

Although the data types and values ​​of $x and $y are different, the "==" operator is used for comparison, and the output result is " The values ​​of variables x and y are equal".

2. "===" operator

The "===" operator is the congruence operator in PHP, which is used to compare two variables. Whether both value and data type are equal. For example:

$x = 4;
$y = "4";
if ($x === $y) {
   echo "变量x和y的值和数据类型都相等";
}

In the above example, the values ​​of $x and $y are equal, but the types are different. Therefore, using the "===" operator for comparison will result in false and nothing will be output.

3. The difference between “==” and “===”

1. Comparison type

“==” The operator only compares the values ​​of variables for equality, regardless of whether the variable types are equal. The "===" operator compares whether the values ​​and types of variables are equal.

2. Comparison results

When the two variable types and values ​​are equal, the results of using the "==" operator and the "===" operator are both true . But when the types of variables are different, the results of using the "==" operator and the "===" operator may be different.

For example, in the following example:

$x = 1;
$y = "1";
if ($x == $y) {
   echo "值相等";
}

if ($x === $y) {
   echo "值和类型都相等";
}

Use the "==" operator for comparison, the output result is "equal values"; use the "===" operator for comparison, no Output anything.

4. Usage scenarios

1. It is recommended to use the "===" operator

In most cases, it is recommended Use the "===" operator for variable comparison. This ensures the accuracy of the comparison results and avoids some unexpected comparison results.

2. Scenarios of using the "==" operator

When some type conversion is required, the "==" operator can be used. For example, when you need to convert a string to an integer, you can use the "==" operator, as shown below:

$x = "4";
if ($x == 4) {
   echo "转换成功";
}

3. Other scenarios

In some other scenarios , when performing array comparison, you can use the "==" operator.

$x = array("a" => "apple", "b" => "banana");
$y = array("a" => "apple", "b" => "banana");
if ($x == $y) {
   echo "数组相等";
}

In short, the choice of operator needs to be decided according to the actual situation, and in most cases, it is recommended to use the "===" operator for variable comparison to ensure the correctness of the comparison results.

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