Question

Basically I need a truly compile-time string hashing in C++. I don’t care about technique specifics, can be templates, macros, anything. All other hashing techniques I’ve seen so far can only generate hashtable (like 256 CRC32 hashes) in compile time, not a real hash.

In other words, I need to have this

printf("%d", SOMEHASH("string"));

to be compiled as (in pseudo-assembler)

push HASHVALUE
push "%d"
call printf

even in Debug builds, with no runtime operations on string. I am using GCC 4.2 and Visual Studio 2008 and I need the solution to be OK for those compilers (so no C++0x).

Answer 1

The trouble is that in C++03 the result of subscripting a string literal (i.e. access a single character) is not a compile-time constant suitable for use as a template parameter.

It is therefore not possible to do this. I would recommend you to write a script to compute the hashes and insert them directly into the source code, i.e.

printf("%d", SOMEHASH("string"));

gets converted to

printf("%d", 257359823 /*SOMEHASH("string")*/ ));