Specifying the Linkage Convention

Use the #pragma linkage and #pragma argument directives to specify the linkage convention. See Table 1 and Accessing ILE C Procedures from Any ILE Program for more information on using these directives.

When specifying linkage conventions, consider the following C++ characteristics:

A C++ program uses the standard OS linkage calling convention. Use the #pragma linkage directive to flag the function call as an external program call.
When you call C++ functions, you must make sure that the sender and receiver both agree on the type of parameter being passed, whether it is by pointer or by value, and whether parameters are widened. For example, if the function you are calling was declared as extern "C nowiden", you must use the #pragma argument(func, nowiden) directive in the function declaration in ILE C.
You can declare a C++ function as external by explicitly declaring the function within the C++ code using either extern "C" or extern "C nowiden". You can add #ifdef statements to the function declarations in the header files used by both C and C++ modules, as shown in Figure 1.

Figure 1. An ILE C++ Function Declared As an External Function

#ifdef __cplusplus
 extern "C" {
   #endif
   function declarations
   #ifdef __cplusplus
       }
   #endif

Note: These statements are declared with C linkage.