Win32 API to enumerate dll export functions?

dumpbin /exports is pretty much what you want, but that's a developer tool, not a Win32 API.

LoadLibraryEx with DONT_RESOLVE_DLL_REFERENCES is heavily cautioned against, but happens to be useful for this particular case – it does the heavy lifting of mapping the DLL into memory (but you don't actually need or want to use anything from the library), which makes it trivial for you to read the header: the module handle returned by LoadLibraryEx points right at it.

#include <winnt.h>
HMODULE lib = LoadLibraryEx("library.dll", NULL, DONT_RESOLVE_DLL_REFERENCES);
assert(((PIMAGE_DOS_HEADER)lib)->e_magic == IMAGE_DOS_SIGNATURE);
PIMAGE_NT_HEADERS header = (PIMAGE_NT_HEADERS)((BYTE *)lib + ((PIMAGE_DOS_HEADER)lib)->e_lfanew);
assert(header->Signature == IMAGE_NT_SIGNATURE);
assert(header->OptionalHeader.NumberOfRvaAndSizes > 0);
PIMAGE_EXPORT_DIRECTORY exports = (PIMAGE_EXPORT_DIRECTORY)((BYTE *)lib + header->
    OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
assert(exports->AddressOfNames != 0);
BYTE** names = (BYTE**)((int)lib + exports->AddressOfNames);
for (int i = 0; i < exports->NumberOfNames; i++)
    printf("Export: %s\n", (BYTE *)lib + (int)names[i]);

Totally untested, but I think it's more or less correct. (Famous last words.)

Go over to Microsoft research and grab the Detours Library. One of its examples does exactly what you are asking. The whole library basically makes detouring/rerouting win32 function calls extremely easy. Its pretty cool stuff.

Detours

Edit: Also note that if you just want to look at the export table, you can (at least in visual studios) set your project properties to print out the export/import tables. I can't remember the exact option but should be easy to google.

**Edit2:**The option is Project Properties->Linker->Debugging->Generate MapFile ->Yes(/MAP)

If you're just looking for a way to find out what functions are exported in a DLL, you can use Microsoft's dependency walker (depends.exe). This wont help you if you actually need to discover the exports programmatically, though.

It's been 12 years since this was asked, but wanted to point out some problems with the solutions presented.

None of them account for ordinals (exports without a name string). Complicated by potential gaps between ordinal indexes. Ordinals have a starting base (the "Base" field of IMAGE_EXPORT_DIRECTORY) but there is no guarantee that ordinal numbers are sequential.

Don't want to spend the time to code it up, but one way to do it is iterate by index 0 to NumberOfFunctions.
Then in a 2nd (inner) loop match that index up in 0 to NumberOfNames into the AddressOfNameOrdinals array.
If you match the function index to the AddressOfNameOrdinals array index, that is your index into AddressOfNames array (an offset you have to resolve). If you don't get a match (over NumberOfNames indexes) then it's an ordinal export.
If the function index in the AddressOfFunctions entry is 0 then it's just an ordinal gap and you skip to the next index.
To get the actual ordinal number (for printing out as a string) you add "Base" to the NumberOfFunctions loop index.