What is the difference between 'extern' and 'externdef' ?

[megavlad]

question in title

[Vortex]

The externdef directive is a combination of public and extern all rolled into one. It uses the same syntax as the extern directive, that is, you place a list of name:type entries in the operand field. If MASM does not encounter another definition of the symbol in the current source file, externdef behaves exactly like the extern statement. If the symbol does appear in the source file, then externdef behaves like the public command. With externdef there really is no need to use the public or extern statements unless you feel somehow compelled to do so.

The important benefit of the externdef directive is that it lets you minimize duplication of effort in your source files. Suppose, for example, you want to create a module with a bunch of support routines for other programs. In addition to sharing some routines and some variables, suppose you want to share constants and macros as well. The include file mechanism provides a perfect way to handle this. You simply create an include file containing the constants, macros, and externdef definitions and include this file in the module that implements your routines and in the modules that use those routines:

https://www.plantation-productions.com/Webster/www.artofasm.com/DOS/ch08/CH08-10.html#HEADING10-109

[megavlad]

Thanks