Using Linkage Specifications in C++

In the following example, a function is prototyped in a piece of C++ code and uses, by default, C++ linkage. 
void CXX_FUNC (int);    // C++ linkage

Note that C++ is case-sensitive, but PL/I, COBOL, assembler, and FORTRAN are not. In these languages, external names are mapped to uppercase. To ensure that external names match across interlanguage calls, code the names in uppercase in the C++ program, supply an appropriate #pragma map specification, or use the NOLONGNAME compiler option. This will truncate and uppercase names for functions without C++ linkage.

To reference functions defined in other languages, you should use a linkage specification with a literal string that is one of the following:
For example, the following specification declares the two functions ASMFUNC1 and ASMFUNC2 to have operating system linkage. The function names are case-sensitive and must match the definition exactly. You should also limit identifiers to 8 or fewer characters. 
  extern "OS" {
    int ASMFUNC1(void);
    int ASMFUNC2(int);
  }

Use the reference type parameter (type&) in C++ prototypes if the called language does not support pass-by-value parameters or if the called routine expects a parameter to be passed by reference.

Note: To have your program be callable by any of these other languages, include an extern declaration for the function that the other language will call.
Parent topic: Using Linkage Specifications in C or C++