To use this convention, you must use the _System keyword in the declaration of the function or set the /Ms compiler option.
Note: Because the IBM C and C++ Compilers library functions use the _Optlink convention, if you use the /Ms compiler option, you must include all appropriate library header files to ensure the functions are called with the correct convention.
The following rules apply to the _System calling convention:
Note: The __parmdwords function may not yield the correct value in the case of compilers that do not follow the rule of passing the size of the parameter list in AL. You can use the __parmdwords function with code compiled under IBM C and C++ Compilers for OS/2 provided the code was compiled with the /Gp+ compiler option.
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Examples Using the _System Calling
Convention in OS/2
_System Calling Convention in
Windows