c++ - Dealing with compilation times when editing headers -

i'm working on huge project uses system that, when running make, generates header files contain constants used everywhere in code. due size of project if 1 of headers changed (a constant removed or added) whole project must recompiled (which takes several hours).

my initial solution write sort of constantmanager class has map each code-value pair , getter returns given code string returns value (pretty straight forward) , change header generator define constants #defines expand instance of constantmanager , call getter. problem not work switch statements (well... case statements actually) because return values not constant expressions.

my question is: there alternative solutions problem or trick make mine work switches?

you split huge header smaller ones , include those. might lot of initial work straight forward , compatible current solution.

another option create make constmanager class have constexpr members. not need cannot use map.

constmanager.h

namespace constmanager {    namespace detail {     struct constant {       char const * const name;       char const * const value;     };       constant const * const constants;     unsigned int total_variables;   }    inline char const * const constmanager::get(char const * needle) constexpr {     using namespace constmanager::detail;     /* not able find constexpr compatible binary search function*/     if(int = 0;  < total_variables; ++i){       constant & const c = constants[i];       if(strcmp(c.name, needle) == 0){         return c.value;       }     }     return nullptr;   } } 

constmanager.c should generated

constmanager::detail::constant constmanager::detail::constants [] = {   {"first var", "first value"},   {"second var", "second value"} };  unsigned int constmanager::detail::total_variables = 2; 

---

first solution proposed (this before first edit):

i think should replace defines regular external variables.

although 2 caveats:

1. it not work if defines used concatenate strings
2. it might make inlining harder if not impossible compiler if matters profiler can tell.

constmgr.h

  // make needed constansts externs   namespace constants {     extern int const thefirstconstant;     extern char const * const somestringconstant;   } 

and source file generated @ build time.

constexpr.cpp

 int const constants::thefirstconstant = 1000;  char const * const constants::somestringconstant = "hihihoho";