Compile-time assertion?

Question

Is there a way I can assert that two constant expressions are equal at compile time?

e.g. I want this to cause a compile-time error

enum { foo=263, bar=264 }; SOME_EXPRESSION(foo,bar) 

but I want this to not cause an error

enum { foo=263, bar=263 }; SOME_EXPRESSION(foo,bar) 

---

edit: the above was simplified. My situation is more like

some_other_file_I_dont_control.h:

class X { public:    enum { foo=263 }; } 

my_file.h:

enum { bar=something+somethingelse }; // bar should equal X::foo SOME_EXPRESSION(X::foo, bar) 

Answer 1

Yes. You can do this with template specializations on type bool, like this:

// empty default template template <bool b> struct StaticAssert {};  // template specialized on true template <> struct StaticAssert<true> {     static void assert() {} };  int f() {     StaticAssert<1==1>::assert();   // compiles fine, assert() member found     StaticAssert<1==2>::assert();   // compile failure, no assert() member for StaticAssert<false> } 

Code is basically from memory, may need some tweaks.

Answer 2

See static_assert (C++0x only); if on an older version, see Boost's StaticAssert.