问C++11:打印“双”作为十六进制？

EN

#include <iostream>
using std::cout; using std::endl;

int main()
{
    double test = -0x123.abc42p+10;
    cout << std::fixed;         // Change from the default for demo
    cout << test << endl;       // Display in "Current" format
    auto fSave = cout.flags();  // Save current flags
    cout << std::hexfloat;      // Change to HEX float
    cout << test << endl;       // ... and display
    cout.setf(fSave, std::ios_base::floatfield); // Restore float field
    cout << test << endl;       // Restored to previous settings!
    return 0;
}

// Include cstdarg / stdarg.h prior to gmp.h in the case
// we want va_list functions like gmp_vfprintf.
#include <cstdarg>
#include <gmp.h>

void func (double d)
{
    gmp_printf ("%a", d);
}

#include <iostream>

void func (std::ostream& ost, double d)
{
    auto len = gmp_snprintf (nullptr, 0, "%a", d);
    char str[1 + len];
    gmp_sprintf (str, "%a", d);
    ost << str;
}