are gcc-3 binaries compatible with gcc-4

I have a static library that has been compiled with gcc 3.4.3 .I would like to use this in code that will now be compiled with gcc-4. I've read vaguely that gcc-3 and gcc-4 binaries are not compatible and that the library will need to be recompiled , but just want confirmation on this. Isn't there anyway a gcc-3 library can be used with gcc-4 ?