c++ - std::make_unsigned 没有给出预期的结果

Question

我有这样的东西:

template<class T>
class SomeClass {
public:
    typedef std::make_unsigned<T> unsigned_t;
    unsigned_t maxBinBitRep_ { - 1 };    
};

int main() {
    // Okay prints out 255 as expected.
    SomeClass<unsigned char>  unsignedChar;  // unsigned version
    // New to `make_unsigned<>` but should print 255.
    //std::cout << unsignedChar.maxBinBitRep << std::endl; 

    // Should be printing the same as above however it's printing: 4294967295
    SomeClass<char> signedChar;
    // same as above.
    //std::cout << signedChar.maxBinBitRep << std::endl; // signed version


    std::cout << "/nPress any key and enter to quit./n" );
    char q;
    std::cin >> q;

    return 0;
}

我正在尝试获取传递到模板参数列表中的 integral 类型，并制作它的 unsigned 版本并将其初始化为 -1 。这应该为我提供任何 integral type 所需的值。

我是否正确使用了 std::make_unsigned？

我的错误 遗漏了声明中的关键字 class...已修复打字错误。

---

编辑 - 我的实际类(class):

template<class T>
class showBinary {
public:
    static const std::size_t standardByteWidth_ { 8 };  
private:
    typedef std::make_unsigned<T> unsigned_t;
    unsigned_t maxVal_ { -1 };

    T t_;
    std::vector<unsigned> bitPattern_;
    std::size_t size_ = sizeof( T );        

public:
    explicit showBinary( T t ) : t_( t ) {

        bitPattern_.resize( size_ * standardByteWidth_ );
        for ( int i = ((maxVal_ + 1) / 2); i >= 1; i >>= 1 ) {
            if ( t_ & i ) {
                bitPattern_.emplace_back( 1 );
            } else {
                bitPattern_.emplace_back( 0 );
            }
        }
    }    

    template<typename U>
    friend std::ostream& operator<<( std::ostream& out, const showBinary<U>& val ) {
        std::ostringstream ostring;
        ostring << "Val: " << val.t_ << " ";
        ostring << "Max Value: " << val.maxVal_ << "\n";
        ostring << "Size in bytes: " << val.size_ << " ";
        ostring << "Number of bits: " << val.size_ * val.standardByteWidth_ << "\n";

        ostring << "Bit Pattern: ";

        for ( auto t : val.bitPattern_ ) {
            ostring << t;
        }
        ostring << std::endl;

        out << ostring.str();
        return out;
    }

};

它的用途:

int main() {
    showBinary<unsigned char> ucBin( 5 );
    showBinary<char> scBin( 5 );
    std::cout << ucBin << std::endl;
    std::cout << scBin << std::endl;

    std::cout << "\nPress any key and enter to quit." << std::endl;
    char q;
    std::cin >> q;

    return 0;        
}

Answer 1

Am I using std::make_unsigned correctly?

不完全是。修复:

typedef typename std::make_unsigned<T>::type unsigned_t;

---

您可以使用 std::bitset<>::to_string 将任何整数类型的值转换为其二进制字符串表示形式功能:

template<class T>
std::string as_binary_string(T value) {
    return std::bitset<sizeof(T) * 8>(value).to_string();
}