Question

I have to convert some C/C++ code to Java. My C++ is extremely rusty.

In a .h file, I have the following:

#ifdef __cplusplus
extern "C" {
#endif

/* tons of declarations */

#ifdef __cplusplus
} /* extern C */
#endif

What is the use of extern "C"? What does it mean? Is it telling the compiler that corresponding code should be interpreted as pure C, rather than C++?

EDIT

Thanks for the answers so far. The history of the code I have to convert is that it seems like a part was written in C first, then the rest was written in C++. So my header file seems to correspond to ‘old’ C code.

I’ll convert this code into a public final class with static method and attributes. No overriding.

Answer 1

It’s telling the compiler that function signatures should be C compatible. Name mangling are different in C and C++ (i.e. C++ supports method overloading while C does not) so in order to make some function calls (i.e. some DLL dynamic calls) compatible with C signature, you use extern C in C++ code.

Take a look at this StackOverflow question for a great explanation on the topic.