This is common practice. Here's why. In C++ this
#ifdef __cplusplus
extern "C" {
#endif
………./*some function,struct*/
#ifdef __cplusplus
}
#endif
compiles as
extern "C" {
………./*some function,struct*/
}
As you identify, this declares C linkage, usually to a precompiled C
library, or to make a C-compatible library. The extern must be conditional,
because in pure C this form of extern is a syntax error.
So what happens in pure C? The #ifdef section is skipped because
__cplusplus is undefined. So it just compiles as
………./*some function,struct*/
In other words, just C definitions, which will have C linkage by default.
This allows a header file for a C library to be compiled in C, and to be
compiled in C++ with suitable linkage.
(You should not see // in this section, because in pure C it is forbidden).
On 7 March 2017 at 16:45, bigpig <bigpig1...@gmail.com> wrote:
> I see some code like this in iOS project:
>
> #ifdef __cplusplus
> extern "C" {
> #endif
>
> ……….//some function,struct
>
>
> #ifdef __cplusplus
> }
> #endif
> if there is C++ compiler and use C linkage,but if there isn’t C++ compiler
> then use what?
> And what is the reason of using this way in code?
>
> Thanks!
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