C++ compile time function execution

Question

I have string tags in my code that are converted to numbers and used to search values in a tag-value structure.

I have something like this:

void foo(         


        

Answer 1

You cannot operate on string literals at compile-time, so what you want isn't feasible in the way you suggested. However, if you're contemplating to process these strings at compile-time, then this means you know all strings at compile-time, and from that you might arrive at acceptable approximations to what you want.

The code you showed implies that the number generation (let's call it a hash) is invoked every time someone searches for a tag. Would reducing this to one invocation be acceptable? If so, you could define constants and use these instead of strings:

const int SomeTag       = toNumber("SomeTag"      ); 
const int SomeOtherTag  = toNumber("SomeOtherTag" ); 
const int YetAnotherTag = toNumber("YetAnotherTag"); 
// ... 

Then, simply replace all occurances of search("SomeTag") by search(SomeTag).

If there's a great number of tags, typing the above could be very tedious, in which case a macro might help:

#define DEFINE_TAG(Tag_) const int Tag_ = toNumber(#Tag_); 

DEFINE_TAG(SomeTag); 
DEFINE_TAG(SomeOtherTag); 
DEFINE_TAG(YetAnotherTag); 
// ... 

#undef DEFINE_TAG