我有一个以下模板化的结构：
template<int Degree>
struct CPowerOfTen {
enum { Value = 10 * CPowerOfTen<Degree - 1>::Value };
};
template<>
struct CPowerOfTen<0> {
enum { Value = 1 };
};
这将是这样使用的：
const int NumberOfDecimalDigits = 5; const int MaxRepresentableValue = CPowerOfTen<NumberOfDecimalDigits>::Value - 1; // now can use both constants safely - they're surely in sync
现在该模板要求Degree为非负数.我想为此强制执行编译时断言.
~CPowerOfTen() {
compileTimeAssert( Degree >= 0 );
}
但由于它没有被直接调用,因此Visual C 9决定不实例化它,因此根本不评估编译时断言语句.
如何对Degree为非负的强制执行编译时检查？
解决方法
template<bool> struct StaticCheck;
template<> struct StaticCheck<true> {};
template<int Degree>
struct CPowerOfTen : StaticCheck<(Degree > 0)> {
enum { Value = 10 * CPowerOfTen<Degree - 1>::Value };
};
template<>
struct CPowerOfTen<0> {
enum { Value = 1 };
};
编辑：没有无限递归.
// Help struct
template<bool,int> struct CPowerOfTenHelp;
// positive case
template<int Degree>
struct CPowerOfTenHelp<true,Degree> {
enum { Value = 10 * CPowerOfTenHelp<true,Degree - 1>::Value };
};
template<>
struct CPowerOfTenHelp<true,0> {
enum { Value = 1 };
};
// negative case
template<int Degree>
struct CPowerOfTenHelp<false,Degree> {}
// Main struct
template<int Degree>
struct CPowerOfTen : CPowerOfTenHelp<(Degree >= 0),Degree> {};
