Detailed explanation of PHP function_exists() function usage

In PHP development, sometimes we need to determine whether a function is available, then we can use the function_exists() function. This article will introduce the usage of function_exists() function in detail.

1. What is the function_exists() function?

The function_exists() function is a built-in function that comes with PHP and is used to determine whether a function is defined. This function returns a Boolean value, True if the function exists, False otherwise.

2. How to use

The syntax of function_exists() function is as follows:

bool function_exists (string $function_name)

Among them, $function_name means to judge The function name can be a function name in the form of a string or an array of callback type. The example is as follows:

1. Determine whether an ordinary function exists

$funcName = 'myFunction';

if ( function_exists( $funcName ) ) {

echo “函数$funcName存在！”;

} else {

echo “函数$funcName不存在！”;

}

2. Determine whether the class method exists

$className = 'MyClass';
$methodName = 'myMethod';

if ( method_exists( $className, $methodName ) ) {

echo “方法$methodName 存在！”;

} else {

echo “方法$methodName不存在！”;

}

3. Precautions for use

1. The function_exists() function can only determine whether the function name exists, but cannot determine whether the function is defined. If the function is defined but not executed, the function_exists() function will still return True.

2. Function names are case-sensitive.

3. For functions with namespaces, you need to write out their full names for judgment.

4. Summary

The function_exists() function is a commonly used function in PHP and is very practical when determining whether a function exists. Through the detailed introduction in this article, I believe you have mastered the usage of the function_exists() function. I hope this article can be helpful to PHP beginners.

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