如果你希望将签名的封顶与“不签名”合并起来,则可以在编辑时确定签名。

#include <iostream>
#include <cstddef> // for pytdiff_t, intptr_t

template <typename T> static inline  bool is_signed() { 
    return ~T(0) < T(1);
}
template <typename T> static inline  T min_value() {
    return is_signed<T>() ? ~T(0) << (sizeof(T)*8-1) : T(0); 
}
template <typename T> static inline  T max_value() { 
    return ~min_value<T>();
}

#define REPORT(type) do{ std::cout
    << "<" #type "> is " << (is_signed<type>() ? "signed" : "unsigned")
    << ", with lower limit " << min_value<type>()
    << " and upper limit " << max_value<type>()
    << std::endl; }while(false)

int main(int argc, char* argv[]) {
    REPORT(char);  // min, max not numeric
    REPORT(int);
    REPORT(unsigned);
    REPORT(long long);
    REPORT(unsigned long long);
    REPORT(ptrdiff_t);
    REPORT(size_t);
    REPORT(uintptr_t);
    REPORT(intptr_t);
}

根据两个补充代表的合理假设:

template<typename T> struct maxval;

template<> struct maxval<unsigned char>
{
  static const unsigned char value = (unsigned char) ~0;
};

template<> struct maxval<signed char>
{
  static const signed char value = ((unsigned char) ~0) >> 1;
};

template<> struct maxval<unsigned short>
{
  static const unsigned short value = (unsigned short) ~0;
};

template<> struct maxval<short>
{
  static const short value = ((unsigned short) ~0) >> 1;
};

int
main ()
{
  std::cout << (int)maxval<signed char>::value << std::endl;
}

同样,其他类型也是如此。

在确定最高价值时,需要区分已签署和未签署类型。 简便的方法就是列举上述例子中的所有内容。

或许可以通过以下几种组合进行:enable_if 和std:is_unsign,但实施(无头盔!)仍需要列举所有类型。

对于未签字的类型,其简单之处是:T(-1)将始终是这种类型的最高限度(-1被削减为最适合范围的最大模块,总是给予该类型的最大上限)。

For signed integer types, the job is almost as easy, at least in practice: take the maximum unsigned value, shift right one bit, and cast to signed. For C99 or C++11 that will work because only three representations for integers (1 s complement, signed magnitude and 2 s complement) are allowed (and it gives the correct result for all three). In theory, for C89/90 and/or C++98/03, it might be possible to design a conforming signed type for which it would fail (e.g., a biased representation where the bias was not range/2).

对这些人和浮动点类型(没有签名的对口单位)来说,工作难度更大。 这样做的理由不是要由你自己来计算。

Edit: As far as how to implement this for in C++, most of the difficulty is in specializing a template for an unsigned type. The most obvious way to do that is probably to use SFINAE, with an expression that will only be legal for a signed type (or only for an unsigned type). The usual for that would be an array whose size is something like T()-1>0. This will yield false for a signed type, which will convert to 0; since you can t create a zero-sized array, that attempted substitution will fail. For an unsigned type, the -1 will "wrap" to the maximum value, so it would create a size of 1, which is allowed.

由于这似乎属于家务劳动,因此我不想显示实际的、工作上的执行。

This works for unsigned types:

template <typename t>
constexpr t max_val() { // constexpr c++11 thing, you can remove it for c++03
  return ~(t(0));
}

由于你可以假定借方和编码的数量,因此可以找到签名。