The in_array() function in PHP is a built-in function that is used to check if a specific value exists within an array and returns a boolean result. Returns true if the value is found and false if the value is not found.

Syntax:

bool in_array(mixed $needle, array $haystack, bool $strict = false)

In this syntax:

• $needle (mixed): The value to search for in the array.
• $haystack (array): The array in which to search.
• $strict (bool, optional): If set to true, the function will also check the types of the $needle and the array elements.
• Defaults to false (non-strict comparison).

Return Value

• Returns true if $needle is found in $haystack.
• Returns false if $needle is not found.

How in_array() Works?

The in_array() function in the PHP works in the following ways:

• By default, in_array() performs a loose comparison (==) between $needle and the array elements.
• If $strict is true, it performs a strict comparison (===) which checks both the value and the type.
• This behavior is important when searching in arrays with mixed types (e.g., strings, integers, floats).

Now, let us understand with the help of the example:

<?php
  $fruits = ["apple", "banana", "orange"];
if (in_array("banana", $fruits)) {
    echo "Banana is in the list!";
} else {
    echo "Banana is not found.";
}
?>

Banana is in the list!

1. Using in_array() with Numbers

This example demonstrates how in_array() checks for both numeric and string values in an array using loose comparison.

<?php
$numbers = [1, 2, 3, "4"];
var_dump(in_array(3, $numbers));      
var_dump(in_array("4", $numbers));    
var_dump(in_array(5, $numbers));      
?>

bool(true)
bool(true)
bool(false)

2. Strict Type Checking

This example illustrates how in_array() uses strict mode to compare both value and type when searching in an array.

<?php
 $numbers = [1, 2, 3, "4"];
var_dump(in_array(4, $numbers, true));   
var_dump(in_array("4", $numbers, true));  
?>

bool(false)
bool(true)

3. Case Sensitivity

This example highlights in_array()’s case-sensitive behavior when searching for string values inside an array.

<?php
  $colors = ["Red", "Green", "Blue"];

var_dump(in_array("red", $colors));  // false, "red" != "Red"
var_dump(in_array("Red", $colors));  // true

?>

bool(false)
bool(true)

4. Searching in Multidimensional Arrays

in_array() does not search inside nested arrays automatically:

<?php
  $array = [
    ["id" => 1, "name" => "anjali"],
    ["id" => 2, "name" => "arti"]
];
var_dump(in_array("anjali", $array));  
?>

bool(false)

To search deeply in multidimensional arrays, you need to use custom functions or array functions like array_column():

<?php
  if (is_array($array)) {
    $names = array_column($array, 'name');
    if (in_array("anjali", $names)) {
        echo "anjali is found!";
    }
} else {
    echo "Input data is not valid.";
}
?>

Input data is not valid.

Common Use Cases for in_array()

• Form validation: Check if a submitted value is among the allowed options.
• User permissions: Verify if a user role exists in the allowed roles array.
• Filtering: Decide whether to include/exclude elements based on a list.
• Control flow: Execute code conditionally based on presence of values.

Best Practices

• Use the $strict parameter to avoid unexpected matches, especially when working with numeric strings and integers.
• For multidimensional arrays, consider flattening or using array functions like array_column().
• For case-insensitive checks, manually normalize the case before searching.
• Remember that in_array() only searches the first-level array elements.

Conclusion

The PHP in_array() function is a straightforward and handy tool for checking if a value exists within an array. Its flexibility with the optional strict type checking and compatibility with various data types make it a staple in PHP programming. Remember its limitations in multidimensional arrays and case sensitivity to use it effectively.