我在用着这个帖子 https://stackoverflow.com/a/53691931/3336423用一些额外的信息来扩展 nan 值和这个帖子 https://stackoverflow.com/a/35272035/3336423修改std::cout行为并显示此额外信息。
这是定义函数和的代码NumPut class:
#include <iostream>
#include <assert.h>
#include <limits>
#include <bitset>
#include <cmath>
#include <locale>
#include <ostream>
#include <sstream>
template <typename T>
void showValue( T val, const std::string& what )
{
union uT {
T d;
unsigned long long u;
};
uT ud;
ud.d = val;
std::bitset<sizeof(T) * 8> b(ud.u);
std::cout << val << " (" << what << "): " << b.to_string() << std::endl;
}
template <typename T>
T customizeNaN( T value, char mask )
{
T res = value;
char* ptr = (char*) &res;
assert( ptr[0] == 0 );
ptr[0] |= mask;
return res;
}
template <typename T>
bool isCustomNaN( T value, char mask )
{
char* ptr = (char*) &value;
return ptr[0] == mask;
}
template <typename T>
char getCustomNaNMask( T value )
{
char* ptr = (char*) &value;
return ptr[0];
}
template <typename Iterator = std::ostreambuf_iterator<char> >
class NumPut : public std::num_put<char, Iterator>
{
private:
using base_type = std::num_put<char, Iterator>;
public:
using char_type = typename base_type::char_type;
using iter_type = typename base_type::iter_type;
NumPut(std::size_t refs = 0)
: base_type(refs)
{}
protected:
virtual iter_type do_put(iter_type out, std::ios_base& str, char_type fill, double v) const override {
if(std::isnan(v))
{
char mask = getCustomNaNMask(v);
if ( mask == 0x00 )
{
out = std::copy(std::begin(NotANumber), std::end(NotANumber), out);
}
else
{
std::stringstream maskStr;
maskStr << "(0x" << std::hex << (unsigned) mask << ")";
std::string temp = maskStr.str();
out = std::copy(std::begin(CustomNotANumber), std::end(CustomNotANumber), out);
out = std::copy(std::begin(temp), std::end(temp), out);
}
}
else
{
out = base_type::do_put(out, str, fill, v);
}
return out;
}
private:
static const std::string NotANumber;
static const std::string CustomNotANumber;
};
template<typename Iterator> const std::string NumPut<Iterator>::NotANumber = "Not a Number";
template<typename Iterator> const std::string NumPut<Iterator>::CustomNotANumber = "Custom Not a Number";
inline void fixNaNToStream( std::ostream& str )
{
str.imbue( std::locale(str.getloc(), new NumPut<std::ostreambuf_iterator<char>>() ) );
}
一个简单的测试函数：
template<typename T>
void doTest()
{
T regular_nan = std::numeric_limits<T>::quiet_NaN();
T myNaN1 = customizeNaN( regular_nan, 0x01 );
T myNaN2 = customizeNaN( regular_nan, 0x02 );
showValue( regular_nan, "regular" );
showValue( myNaN1, "custom 1" );
showValue( myNaN2, "custom 2" );
}
我的主要程序：
int main(int argc, char *argv[])
{
fixNaNToStream( std::cout );
doTest<double>();
doTest<float>();
return 0;
}
doTest<double>输出：
Not a Number (regular): 0111111111111000000000000000000000000000000000000000000000000000
Custom Not a Number(0x1) (custom 1): 0111111111111000000000000000000000000000000000000000000000000001
Custom Not a Number(0x2) (custom 2): 0111111111111000000000000000000000000000000000000000000000000010
doTest<float>输出：
Not a Number (regular): 01111111110000000000000000000000
Not a Number (custom 1): 01111111110000000000000000000001
Not a Number (custom 2): 01111111110000000000000000000010
虽然我期望float:
Not a Number (regular): 01111111110000000000000000000000
Custom Not a Number(0x1) (custom 1): 01111111110000000000000000000001
Custom Not a Number(0x2) (custom 2): 01111111110000000000000000000010
问题是num_put只有一个虚拟的do_put for double， 不是为了float. So my float被默默地投射到double，丢失我的扩展信息。
我知道有一些替代方案，比如使用FloatFormat从第二篇文章开始，或者只是写一个聪明的float2double函数并在将 NaN 值发送到输出流之前调用它，但它们要求开发人员处理这种情况......他可能会忘记。
有没有办法在内部实现NumPut类或任何其他能让事情正常工作的东西float被发送到灌输者stream就像它适用于double?
我的要求是能够简单地调用类似的函数fixNaNToStream对于任何输出流（std::cout, local std::stringstream, ...) 然后发送float and double并将它们识别为我的自定义 NaN 并相应地显示。
