cannot use namespace and cannot include standard C++ library in my .h files

Question

i'm using C++ Audio processing library for my Swift project from https://www.surina.net/soundtouch/sourcecode.html

I have also included those cpp file in my compile sources in Projects-targets-build phases.

When i try to import all of library header file in my bridging header

#import "SoundTouch.h"

i got error when try to compile it

Unknown type of name 'namespace' in STTypes.h
'stdexcept' file not found

i'm using namespace in my header file

namespace soundtouch { ... } 

i cannot use several standard library also like string

#include <stdexcept>
#include <string>

what i'm missing here?

Answer 1

Swift does not understand C++ even in header files. C does not have namespaces, so when the Swift compiler comes across the word namespace it's going to think the same as the C compiler would, which is that it is the name of a variable. That's not all though. Swift also won't understand other C++ keywords like class nor will it understand C++ style name mangling, even though it does its own name mangling, nor export "C" { ... }.

If you have a C++ header file that you want to import into Swift, you have to make sure all the C++ stuff is hidden with #ifdef __cplusplus just like if you are including the header in a C program. Also, all the function declarations will need to be extern "C" to disable name mangling.

You will need an alternate declaration for classes, you can use void* or I found an incomplete struct type works quite well and you'll need to create C wrapper functions to call functions defined in the class. Something like the following might work (I haven't tested it).

#if defined __cplusplus
extern "C" {
#endif

#if defiend __cplusplus

class Foo
{
    void bar(int c);
}
#endif
struct FooHandle;

void Foo_bar(struct FooHandle* foo, int c);

#if defined __cplusplus
}
#endif

And you'll need to define the shim function in a C++ file

#include MyHeader.h

void Foo_bar(struct FooHandle* foo, int c)
{
    ((Foo*) foo)->bar(c);
}

Apologies if I got the C++ wrong, I haven't used it seriously since 1998