enum

// enum.cpp

#include <iostream>

using namespace std;

enum color
{
    WHITE,
    BLACK,
    RED,
    GREEN,
    BLUE,
    YELLOW,
    NUM_COLORS
};
enum datatype
{
    TYPE_INT8 = 1,
    TYPE_INT16 = 2,
    TYPE_INT32 = 4,
    TYPE_INT64 = 8
};

struct Point
{
    enum datatype type;
    union
    {
        std::int8_t data8[3];
        std::int16_t data16[3];
        std::int32_t data32[3];
        std::int64_t data64[3];
    };
};

size_t datawidth(struct Point pt)
{
    return size_t(pt.type) * 3;
}

int64_t l1norm(struct Point pt)
{
    int64_t result = 0;
    switch (pt.type)
    {
    case (TYPE_INT8):
        result = abs(pt.data8[0]) + abs(pt.data8[1]) + abs(pt.data8[2]);
        break;
    case (TYPE_INT16):
        result = abs(pt.data16[0]) + abs(pt.data16[1]) + abs(pt.data16[2]);
        break;
    case (TYPE_INT32):
        result = abs(pt.data32[0]) + abs(pt.data32[1]) + abs(pt.data32[2]);
        break;
    case (TYPE_INT64):
        result = abs(pt.data64[0]) + abs(pt.data64[1]) + abs(pt.data64[2]);
        break;
    }
    return result;
}

int main()
{
    enum color pen_color = RED;
    pen_color = color(3); // convert int to enum
    cout << "We have " << NUM_COLORS << " pens." << endl;
    // pen_color += 1; //error!
    int color_index = pen_color;
    color_index += 1;
    cout << "color_index = " << color_index << endl;

    // declaration and initialization
    struct Point point1 = {.type = TYPE_INT8, .data8 = {-2, 3, 4}};
    struct Point point2 = {.type = TYPE_INT32, .data32 = {1, -2, 3}};

    cout << "Data width = " << datawidth(point1) << endl;
    cout << "Data width = " << datawidth(point2) << endl;

    cout << "L1 norm = " << l1norm(point1) << endl;
    cout << "L1 norm = " << l1norm(point2) << endl;

    return 0;
}

// enum.c

#include <stdio.h>

int main()
{
    enum day
    {
        Monday = 1,
        Tuesday,
        Wednesday
    };                        // 初始化
    enum day today = Tuesday; // 变量的使用
    printf("%d\n", Wednesday);
    return 0;
}

嵌套 enum

#include <iostream>

class Mat
{
public:
    enum DataType
    {
        TYPE8U,
        TYPE8S,
        TYPE32F,
        TYPE64F
    };

private:
    DataType type;
    void *data;

public:
    Mat(DataType type) : type(type), data(NULL) {}

    DataType getType() const { return type; }
};

int main()
{
    Mat image(Mat::DataType::TYPE8U);

    if (image.getType() == Mat::DataType::TYPE8U)
        std::cout << "This is an 8U matrix." << std::endl;
    else
        std::cout << "I am not an 8U matrix." << std::endl;

    return 0;
}