How to determine whether an array contains a key value in php

In PHP, determining whether an array contains a key value is a very basic operation that must be mastered. Because in daily development, we often need to perform corresponding operations based on the key values ​​in the array, so we need to understand how to determine whether an array contains a specified key value.

1. isset() function

In PHP, the most common way to determine whether an array contains a specified key value is to use the isset() function. This function is used to detect whether the variable has been set and is not NULL. When the specified variable exists and the value is non-null, the isset() function returns true; on the contrary, if the variable does not exist, the value is null, or is unloaded by the unset() function, it returns false.

Therefore, we can use the isset() function to determine whether an array contains a specified key value. The specific method is:

if(isset($array['key'])){
    //存在
}else{
    //不存在
}

In the above code, $array represents the array name to be judged, and ['key'] represents the key name to be judged. If this key exists in this array, it returns true, otherwise it returns false.

2. array_key_exists() function

In addition to using the isset() function, PHP also provides another function to determine whether the array contains a specified key name—— array_key_exists() function. This function is used to check whether the given key name or index exists in the array, and the return value is Boolean.

Compared with the isset() function, the array_key_exists() function is more strict. As long as the array contains the specified key name, regardless of whether its value is null or non-null, this function will return true. Therefore, the usage of the array_key_exists() function is as follows:

if(array_key_exists('key', $array)){
    //存在
}else{
    //不存在
}

In the above code, 'key' represents the key name to be judged, and $array represents the array name to be judged. If this key exists in this array, it returns true, otherwise it returns false.

Compared with the isset() function, the array_key_exists() function is more rigorous and can more accurately determine whether an array contains a specified key name.

3. in_array() function

In addition to the above two methods, PHP also provides a more flexible method-use the in_array() function to determine Whether an array contains a specified key value. The usage of this function is as follows:

if(in_array('value',$array)){
    //存在
}else{
    //不存在
}

In the above code, 'value' represents the key value to be judged, and $array represents the array name to be judged. If this key value exists in this array, it returns true, otherwise it returns false.

It should be noted that the in_array() function can be used to determine whether the array contains a specified value, not just the key value. Compared with isset() function and array_key_exists() function, in_array() function is more flexible and can determine whether any value in the array exists in this array.

To sum up, to determine whether an array contains a specified key value, you can use the isset() function, array_key_exists() function or in_array() function. Different functions are suitable for different scenarios, and we need to choose the appropriate method according to specific needs. At the same time, we also need to note that the return values ​​​​of these functions are all Boolean, so when using them, they need to be processed accordingly according to the actual situation, such as outputting prompt information, continuing to execute subsequent code, etc.

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