How to determine whether key exists in an array in php

In PHP, array is a very common data type that can store multiple values ​​and access these values ​​through subscripts. In actual development, it is often necessary to determine whether a certain key exists in an array. This problem seems simple, but in fact there are some things that need attention.

First of all, PHP provides some functions to determine whether a certain key exists in an array, for example:

1. array_key_exists() function

array_key_exists( ) function is used to determine whether a certain key exists in an array. Its function prototype is as follows:

bool array_key_exists (mixed $key, array $array)

Among them, $key represents the key to be determined key, $array represents the array to be searched. Returns true if $key exists in $array, false otherwise.

For example:

$arr = array("name" => "张三", "age" => 18);
if (array_key_exists("name", $arr)) {
    echo "存在name键";
} else {
    echo "不存在name键";
}

In the above code, because the name key exists in the $arr array, "name key exists" will be output.

2. isset() function

isset() function is used to determine whether a variable is set and is not NULL. Its function prototype is as follows:

bool isset ( mixed $var [, mixed $... ] )

Among them, $var represents the variable to be judged. Returns true if $var is set and not NULL, false otherwise.

For arrays, if you want to determine whether a $key exists, you can use the isset() function, for example:

$arr = array("name" => "张三", "age" => 18);
if (isset($arr["name"])) {
    echo "存在name键";
} else {
    echo "不存在name键";
}

In the above code, because the name key exists in the $arr array, So "name key exists" will be output.

In addition, there is another way to determine whether $key exists - use the array_search() function. The function of this function is to search for the specified value in the array. If found, the value is returned. key, otherwise false is returned. If you want to determine whether a key exists, you can use this function, for example:

$arr = array("name" => "张三", "age" => 18);
if (array_search("name", $arr)) {
    echo "存在name键";
} else {
    echo "不存在name键";
}

In the above code, because the name key exists in the $arr array, "name key exists" will be output.

But it should be noted that the above method is only applicable when $value and $key are both strings. If $key is of other types, it is not recommended to use the array_search() function.

Another thing to note is that if the value corresponding to $key is NULL, both the isset() function and the array_key_exists() function will return false. Therefore, when determining whether $key exists, it is recommended to use the array_key_exists() function.

To sum up, using the array_key_exists() function and isset() function in PHP can effectively determine whether a key exists in an array, while the array_search() function can be used when the value is a string and $ Used when key is also a string. In actual development, it is necessary to choose the appropriate method for judgment based on the specific situation.

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