C++ :: Parse Executable Files - Registering Types To Be Used At Runtime

I'm writing a program that needs to parse executable files. I've got an "executable" base-class, and currently an "elf" class which inherits from it for parsing ELF files, and I will add more parsers (COM, MZ, PE, a.out, MACH-O, whatever) later on.

I want the program to automatically detect which kind of executable it's loading at runtime. It should be easy because every executable format I'm aware of/plan to support starts with a magic number. But because I can't have the parsers not check the file type (what if I re-use the code?), and I don't want to check each file twice (not just for performance, but also because only the ELF parser should know that ELF files start with "x7fELF", etc.) so I've come up with a pretty lazy solution: just try to parse the file with each known parser and have them throw an exception ("exe_type_error") if they can't parse it. If that exception gets thrown, try the next parser; if not, stop.

The remaining problem is how, at runtime, my program will know what parsers are available. I don't want to hard-code it in the main function; instead, I'd like the parsers to "register" themselves as available. That way, if I decide to go down the route of adding new parsers via dynamic linking, I will only have to add an API for dynamic libraries to register their parser, without recompiling any of the main program's code. I also want to do the same thing for another key part of the program (it's a static executable optimizer; it will run a series of "tests" (e.g. "is xor eax, eax faster than mov eax, 0 on this machine?") and optimizations ("if yes, change all mov eax, 0 to xor eax, eax") and I want to load those at runtime too).