Question

拥有（不用担心这段代码的长度，专注于struct X和Range）（你可以复制并粘贴并编译）：
的 EDITED

    #include <limits.h>
#include <type_traits>
//This is from file "Static_limits.h"
template<class T>struct static_numeric_limits;
template<>struct static_numeric_limits<signed char>
{
    enum {min = SCHAR_MIN,max = SCHAR_MAX};
};
/*This "surplus" template is here for the reason that char is threated diferently from signed char */
template<>struct static_numeric_limits<char>
{
    enum {min = SCHAR_MIN,max = SCHAR_MAX};
};
template<>struct static_numeric_limits<unsigned char>
{
    enum {min = 0x0,max = UCHAR_MAX};
};
template<>struct static_numeric_limits<unsigned short>
{
    enum {min = 0x0,max = USHRT_MAX};
};
template<>struct static_numeric_limits<signed short>
{
    enum {min = SHRT_MIN,max = SHRT_MAX};
};
template<>struct static_numeric_limits<unsigned int>
{
    enum {min = 0x0,max = UINT_MAX};
};
template<>struct static_numeric_limits<signed int>
{
    enum {min = INT_MIN,max = INT_MAX};
};
template<>struct static_numeric_limits<unsigned long>
{
    enum {min = 0x0,max = ULONG_MAX};
};
template<>struct static_numeric_limits<signed long>
{
    enum {min = LONG_MIN,max = LONG_MAX};
};
template<>struct static_numeric_limits<unsigned long long>
{
    static const long long min = 0x0;
    static const long long max = ULLONG_MAX;
};
template<>struct static_numeric_limits<signed long long>
{
#define LLONG_MAX     9223372036854775807LL
    /* maximum signed long long int value */
    static const long long min = LLONG_MIN;
    static const long long max = LLONG_MAX;
};
//This is from main.cpp
typedef unsigned long long uint_64;
typedef signed long long int_64;
/*Validates range*/
template<class IntType, uint_64 value_,bool C = std::is_signed<IntType>::value>
struct validate_range;
template<class IntType,uint_64 value_>
struct validate_range<IntType,value_,true>
{
    enum {value = (static_cast<int_64>(value_) >= static_numeric_limits<IntType>::min) &&
                  (static_cast<int_64>(value_) <= static_numeric_limits<IntType>::max)
         };
};
template<class IntType,uint_64 value_>
struct validate_range<IntType,value_,false>
{
    enum {value = (value_ >= static_numeric_limits<IntType>::min) &&
                  (value_ <= static_numeric_limits<IntType>::max)
         };
};
template<class IntType, IntType value>
struct Range
{
private:
    const IntType value_;
protected:
    const IntType getRange()const
    {
        return value_;
}        public:
    Range():value_(value)
    {
        /*eb*/
    }
    //this static assert in here won't work even though this class is a base class for Low
    static_assert((validate_range<IntType, value>::value),"Value constant is out of range");
};
template<class IntType, IntType value>
struct Low : private Range<IntType,value>//HERE Range IS INHERITED BY Low
{
    const IntType getLowRange()const
    {
        return Range<IntType,value>::getRange();
    }
};
template<typename IntType, uint_64 low_range>
struct X : public Low<IntType,low_range>
{};
    //static_assert((validate_range<IntType, Value>::value),"Value constant is out of range");//this static doesn't work if placed in Low's base class namely Range        };
    int main(int argc, char** argv)
    {
        X<unsigned char, -2> x4;//this should fail
        return 0;
    }

所以基本上我在这里问的是为什么static_assert（（validate_range :: value），...如果放在Range结构中不起作用，而Range结构又是Low的基类，而它又是基类的X但是如果直接放在struct X中则有效的 EDITED
伙计们我很抱歉以前的代码。我编辑了我的帖子，这次它应该工作（暴露真正的问题）。再一次，对不起最后一段代码，我只是不知道发生了什么。

Answer 1

这是我得到的错误。他们似乎相当自我解释：

test.cpp:115:45: error: use of undeclared identifier 'Value'; did you mean 'value'?
     static_assert((validate_range<IntType, Value>::value),"Value constant is out of range");
                                            ^~~~~
                                            value
test.cpp:99:37: note: 'value' declared here
    template<class IntType, IntType value>
                                    ^
test.cpp:127:39: error: use of undeclared identifier 'low_range'
        struct X : public Low<IntType,low_range>
                                      ^
test.cpp:128:9: error: expected class name
        {
        ^
3 errors generated.

修改

您的最新帖子为我编译（除了有关重新定义LLONG_MAX的警告之外）。

static_assert放置问题

1 个答案: