Differences between. H,. m, and. mm in objective-C

. H: Header file. The header file contains class, type, function, and constant declarations.
. M:Source codeFile. This is a typical sourceCodeFile Extension, which can contain objective-C and C code.
. Mm:Source code file. Source code files with such extensions can contain not only objective-C and C code, but also C ++ code. This extension is used only when the C ++ class or feature is required in your objective-C code.

When you need to include header files in the source code, you can use the standard # include compilation option, but objective-C provides a better method. The # import option and # include option are identical, but they ensure that the same file is only contained once. Objective-C examples and documents tend to use # import.