I want to get some settings I store in the registry, and if they differ from a #define I want to redefine it, could I do it this way?:

#define DEFINED_X "testSetting"

void LoadConfig()
{
    regConfigX = some value previusly stored in the registry;
    if(regConfigX!=DEFINED_X)
    {
        #undef DEFINED_X
        #define DEFINED_X regConfigX
    }
}

I tought #define was used only when compiling, would this code work when running the compiled exe?