You try to use a c++ lib:
First you translate the .h who define the prototypes.
Headinc (the translator) made the job and you have now a masm header file.
Yuou Try it but you are ennoying by some functions not usable.
Suspect than some of them are written in decorated form in the library.
Masm couldn't find them but he can call them with the proper definitions.
It is the goal of this tool.
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Use dumpbin /ALL on the library (c++ express dumpbin)
You have now a file describing those functions.
Give the two files to the tool.
He write a new file,with the needed definitions by masm.
Use this file as new header.