CODEWITHSUNDEEP
c++macros
David Degea
David Degea

Reputation: 1398

How to trigger the __cplusplus (C++) #ifdef?

#ifdef __cplusplus
// C++ code
#else
// C code
#endif

The structure is this. My question is, how to actually trigger the #ifdef on?

I mean, in program? What code I write can turn #ifdef on?

For example, in this case. is that 

#define __cplusplus

will turn it on?

Upvotes: 17

Views: 26534

Answers (4)

kravemir
kravemir

Reputation: 11026

"#define __cplusplus"

will let it on?

Yes, it will "let it on".

__cplusplus should be automatically defined by C++ compiler. C++ uses different name mangling and the macro often used to make C headers compatible with C++:

#ifdef __cplusplus
extern "C" {
#endif

...

#ifdef __cplusplus
}
#endif

Upvotes: 21

Jerry Coffin
Jerry Coffin

Reputation: 490338

A C++ compiler defines this automatically.

Since this starts with two consecutive underscores, it is reserved. You are not allowed to define it yourself (i.e., attempting to do so gives undefined behavior).

Upvotes: 10

Puppy
Puppy

Reputation: 146968

The C++ Standard enforces that __cplusplus will always be defined in C++ programs. The C Standard obviously does not. This means that the user need go to no effort to enable this machinery.

Upvotes: 13

R. Martinho Fernandes
R. Martinho Fernandes

Reputation: 234584

Just compile it with a C++ compiler and __cplusplus is defined automatically in that case.

Upvotes: 16

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