Re: [Libexif-devel] Using libexif: Question about exif-data.h

[Marcus M. <ma...@je...>]

> #ifdef __cplusplus
> extern "C" {
> #endif /* __cplusplus */
> 
> If __cpluplus is defined, then extern "C" is declared, { is opened, and then
> there is an #endif.  What do these three statements accomplish?
> 
> 
> Near the bottom of the file, another #ifdef __cplusplus statement appears,
> then the } is closed, and another #endif /* __cplusplus */ statement
> appears.
> 
> I do not understand the function of the second #ifdef __cplusplus statement
> just before the }. 
> 
> What is the purpose of the declaration (made somewhere else in the library)
> of __cplusplus?  Where (in what file) is that declaration made?
> 
> All of the other statements in the file exif-data.h are contained between {
> and  } , therefore, apparently controlled by the #ifdef __cplusplus
> statement at the beginning.  Why?

libexif imports functions as "C" functions.

For using libexif in a C++ program you of course need the prototypes, but
the prototypes need to be marked as "C" functions, otherwise they are imported
using C++ mangling of function names.

The extern "C" { ... }; wrapper around the prototypes accomplishes exact that.
The prototypes are visible to C++ code, but as C imports.

Ciao, Marcus