How to determine if a variable is in an array in php

In PHP programming, we often need to determine whether a variable exists in an array. If the variable exists in the array, we can perform subsequent operations, otherwise it may cause program errors or abnormal operation. This article will introduce how to determine whether a variable exists in an array in PHP.

1. in_array() function

PHP’s in_array() function can check whether the specified value exists in the array and return a Boolean value. The syntax is as follows:

in_array($value, $array, $strict);

Where, $value is the value to be found, $array is the array to be found, $strict is an optional parameter, if this parameter is used and is true, check whether $value exists in $array and the types need to be exactly the same.

For example, the following code uses the in_array() function to check whether a numeric variable exists in an integer array:

$variable = 12;
$array = array(10, 20, 30, 40, 50);
if (in_array($variable, $array)) {
    echo "存在于数组中";
} else {
    echo "不存在于数组中";
}

The output result is: exists in the array.

2. array_search() function

PHP’s array_search() function can search for a given value in the array and return the corresponding key name. If the value is not found, false is returned. The syntax is as follows:

array_search($value, $array, $strict);

Where, $value is the value to be found, $array is the array to be found, $strict is an optional parameter, if this parameter is used and is true, check whether $value exists in $array and the types need to be exactly the same.

For example, the following code uses the array_search() function to check whether a string variable exists in a string array:

$variable = "hello";
$array = array("world", "hello", "world!");
$key = array_search($variable, $array);
if ($key !== false) {
    echo "存在于数组中，其键名为: " . $key;
} else {
    echo "不存在于数组中";
}

The output result is: exists in the array, and its key Named: 1.

3. isset() function

PHP’s isset() function can be used to check whether a variable exists and the value is not null. The isset() function returns false if a variable does not exist or has a value of null, otherwise it returns true. Therefore, when we need to check whether a variable exists in the array, we can first check whether the variable exists and is not empty, and then use the in_array() function to judge.

For example, the following code uses the isset() function and the in_array() function combination to determine whether a variable exists in an array:

$variable = "apple";
$array = array("banana", "orange", "apple");
if (isset($variable) && in_array($variable, $array)) {
    echo "存在于数组中";
} else {
    echo "不存在于数组中";
}

The output result is: exists in the array.

To sum up, when we need to determine whether a variable exists in an array, we can use PHP's in_array() function, array_search() function and isset() function to determine. For different scenarios and needs, different functions can be selected to implement corresponding functions.

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