HP aC++/HP C A.06.28 Programmer's Guide Integrity servers (769150-001, March 2014)

10 Mixing C++ with Other Languages
This chapter provides guidelines for linking HP aC++ modules with modules written in HP C and
HP FORTRAN 90 on HP 9000 Series 700/800 systems. It discusses the following topics:
• “Calling Other Languages” (page 188)
• “Data Compatibility between C and C++” (page 188)
• “HP aC++ Calling HP C” (page 189)
• “HP C Calling HP aC++” (page 191)
• “Calling HP FORTRAN 90 from HP aC++” (page 193)
Calling Other Languages
A module is a file that contains one or more variable or function declarations, one or more function
definitions, or similar items logically grouped together. Mixing modules written in C++ with modules
written in C is relatively straightforward since C++ is for the most part a superset of C. Mixing
C++ modules with modules in languages other than C is more complicated.
When creating an executable file from a group of programs of mixed languages, one of them
being C++, you must be aware of the following:
• In general, the overall control of the program must be written in C++. In other words, the main
function should appear in a C++ module and no other outer block should be present.
• You must pay attention to case sensitivity conventions for function names in the different
languages.
• You must make sure that the data types in the different languages correspond. Do not mismatch
data types for parameters and return values.
• Storage layouts for aggregates differ among languages.
• You must use the extern "C" linkage specification to declare modules that are not written
in C++; this is true whether or not the module is written in C.
• You must use the extern "C" linkage specification to declare modules that are written in
C++ and called from other languages.
• Do not use extern "C" when you include standard C header files because these header
files already contain extern "C" directives.
NOTE: HP aC++ classes are not accessible to non-C++ routines.
Data Compatibility between C and C++
Many of the data types between C and C++ are identical as C++ is, for most part, a superset of
C. Both languages support char, short, int, long, float, and double data types. ANSI C
and HP C++ also support a long double type. In addition, HP aC++ supports bool, wchar_t,
long long, and unsigned long long data types.
Pointers, structs, and unions that can be declared in C are also compatible. Arrays composed of
any of the above types are compatible.
C++ classes are generally incompatible with C structs. The following features of the C++ class
facility may cause the compiler to generate extra code, extra fields, or data tables:
• Multiple visibility of members (including both private and public data members in a class)
• Inheritance, either single or multiple
• Virtual functions
188 Mixing C++ with Other Languages