How to determine whether a function is defined in PHP

1. Declare the file type and encoding for PHP interaction with the browser, as shown in the figure:

2. function_exists( ) Function of the function: If the function has been defined, it returns TRUE. The syntax structure is as shown in the figure:

3. Use the function_exists() function to determine whether the show() function has been is defined, the code is as shown in the figure:

Run the web page, output the judgment result of the function_exists() function, and display the result as shown in the figure:

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