C++ program using a C library headers is recognizing "this" as a keyword. Extern "C" error?

Question

My C++ program needs to use an external C library. Therefore, I'm using the

extern "C"
{
   #include <library_header.h>
}

syntax for every module I need to use.

It worked fine until now. A module is using the this name for some variables in one of its header file. The C library itself is compiling fine because, from what I know, this has never been a keyword in C.

But despite my usage of the extern "C" syntax, I'm getting errors from my C++ program when I include that header file.

If I rename every this in that C library header file with something like _this, everything seems to work fine.

The question is:

Shouldn't the extern "C" syntax be enough for backward compatibility, at least at syntax level, for an header file? Is this an issue with the compiler?

Answer 1

Shouldn't the extern "C" syntax be enough for backward compatibility, at least at syntax level, for an header file? Is this an issue with the compiler?

No. Extern "C" is for linking - specifically the policy used for generated symbol names ("name mangling") and the calling convention (what assembly will be generated to call an API and stack parameter values) - not compilation.

The problem you have is not limited to the this keyword. In our current code base, we are porting some code to C++ and we have constructs like these:

struct Something {
    char *value;
    char class[20]; // <-- bad bad code!
};

This works fine in C code, but (like you) we are forced to rename to be able to compile as C++.