Tcl_GetVersion(major, minor, patchLevel, type)
Tcl_GetVersion should be used to query the version number of the Tcl library at runtime. This is useful when using a dynamically loaded Tcl library or when writing a stubs-aware extension. For instance, if you write an extension that is linked against the Tcl stubs library, it could be loaded into a program linked to an older version of Tcl than you expected. Use Tcl_GetVersion to verify that fact, and possibly to change the behavior of your extension.
Tcl_GetVersion accepts NULL for any of the arguments. For instance if you do not care about the patchLevel of the library, pass a NULL for the patchLevel argument.