How to include the two different versions of the same header? - c++

Question

I am writing file conversion code from a proprietary file format to one more generic. My goal is to support multiple versions of the manufacturer's file format.
I have a multiple versions of the same proprietary headers. The headers define various structs which comprise the main file header (the file is simply a large header followed by raw data).
I need to read the first 4 bytes of the source file to determine the file version. The file version, in turn, tells me which version of the C-structs was used to create the file.
The issues are:
I can't modify the proprietary headers
The headers do not use namespaces or classes
There are a good handful of macros defined in the headers
Possible solutions:
Build different converter binaries for each file version type :-(
Inconvenient for both user and developer
Dynamically load libraries for each version
The converter is plugin-oriented, so there's already a lot of this happening
I have tried hacking with namespaces:
namespace version1 {
#include "version1.h"
}
namespace version2 {
#include "version2.h"
}
int main (void) {
version1::header *hdr = new version1::header;
return 0;
}
But this won't work because of include guards, and because there are multiple macros are redefined in each header.
Is there an elegant way to handle this?

Answer 1

You could use two different source files, together with a forward declaration:
// Forward declare in main.cpp:
namespace version1
{
struct header;
}
namespace version2
{
struct header;
}
// version1.cpp:
namespace version1
{
#include <version1.h>
}
version1::header* new_v1_header()
{
return new version1::header;
}
// other functions using `version1::header`
// version2.cpp:
namespace version2
{
#include <version2.h>
}
version2::header* new_v2_header()
{
return new version2::header;
}
// other functions using `version2::header`
Another alternative is to implement a wrapper class, which has a base-class that is just an empty shell:
class header_base
{
virtual int func1(char *stuff) = 0;
... many other virtual functions.
};
// Create implementation of header_v1 or header_v2:
header_base* make_header(unsigned int magic);
header_base.cpp:
#include "header_v1.h"
#include "header_v2.h"
header_base* make_header(unsigned int magic)
{
switch(magic)
{
case Magic_V1:
return new header_v1;
case Magic_V2:
return new header_v2;
default:
assert(0);
return 0;
}
}
and then implement, in two separate
in headerv1.h:
class header_v1 : public header_base
{
int func1(char *stuff);
...
};
header_v1.cpp:
#include "header1.h"
int header_v1::func1(char *stuff)
{
...
return 17;
}
And similar for header_v2.h and header_v2.cpp.