/Hnumber
The /H option restricts the length of external (public) names. The number field accepts an integer specifying the maximum number of significant characters; the compiler considers only the first number characters of external names in the program. The program can contain external names longer than number characters, but the extra characters are ignored.
Without the /H option, the default for C names is 32 characters; this includes any compiler-generated leading underscore (_) or at sign (@). (The compiler adds a leading underscore to names modified by __cdecl (default) calling conventions and a leading at sign to names modified by __fastcall calling conventions.) You can use the /H option to restrict C names to values less than the 32-character default, or you can specify the acceptance of C names up to a limit of 247.
The /H option is ignored for C++ names. Names from C++ programs have no added leading characters. C++; other decorated names have 247 significant characters.
You may find /H useful when creating mixed-language or portable programs.