[Qgis-developer] Patch for compiling qgis-0.8pre2 with geos-3.0.0rc3

[Tom Elwertowski]

Mike Leahy wrote:
> Gary Sherman wrote:
>> Does this mean that it will also compile with GEOS 2.x?
> 
> Sorry, it is 3.x only.  With my very limited understanding of c++ 
> programming, I can only guess if it's even possible to allow compiling 
> against both 2.x and 3.x.

I see several possibilities here:

One is to add the following to each file with removed namespace prefixes.

#if GEOS_VERSION_MAJOR < 3
using namespace geos;
#endif

This is ok for cpp files but not a good idea for h files because it can 
result in name collisions in unexpected places if the h file is widely 
included.

Another idea is to change our prefixes from "geos" to "GEOS" or 
something similar if "GEOS" is already in use and then add the following 
after figuring out what the new namespace is:

#if GEOS_VERSION_MAJOR < 3
#define GEOS geos
#else
#define GEOS geos3whatever
#endif

This technique avoids having headers propagate the "using" clause into 
unexpected places.

Your changes to what geos headers to include may also need a bit of 
adjustment to work with both 2 and 3.

I have not installed GEOS 3 because I thought that the API had changed 
and code needed to be revised. Your patches seem to indicate that 
existing code probably still works and just the namespace has changed.

I will install GEOS 3 and try this myself. Thanks for doing the research.

Tom