does PHP have a equivalent to the C++ #ifndef #define?

I'm coding a really large web page in PHP. One of the problems I run into is I'll create a function in file inc.function.something.php and it will need a function included in inc.function.somethingelse.php. If I require() somethingelse.php in something.php and it's already been required in main.php, I get an error about the function being defined twice. Is there an equivalent to the C++: #ifndef some_header_file_h #define some_header_file_h // insert code that shouldn't be repeated here #endif // some_header_file_h Thanks in advance, Dan Anderson