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

[Benny S. <ich...@pa...>]

In the file exif-data.h, I am confused by some statements.

The file starts with:

*******************************************************

#ifndef __EXIF_DATA_H__
#define __EXIF_DATA_H__

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

..... many other statements......

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* __EXIF_DATA_H__ */

*******************************************************

I understand the statements containing __EXIF_DATA_H__.

Regarding the statements:

#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?

Thanks,

Benny Smith
Santa Rosa, CA