如何避免C++11中收缩转换的错误

Question

我有下面的代码，它使用枚举值来初始化结构的向量。我收到有关窄转换的错误。我参考了 Microsoft 文档：link 我可以通过以下代码解决问题。

#include <iostream>
#include <vector>
#include <string>

enum NUMBERS
{
    NUMBERS_ZERO    = 0xA0000000,
    NUMBERS_ONE     = 0xA0000001,
    NUMBERS_TWO     = 0xA0000002,
    NUMBERS_THREE   = 0xA0000003,
};

struct Person {
    uint32_t        m_id = 0;
    std::string     m_name;

    Person(uint32_t id, std::string name) :
        m_id(id), m_name(name) {}
};

std::vector<Person> PersonList =
{
    {static_cast<uint32_t>(NUMBERS_ZERO),   "abc"},
    {static_cast<uint32_t>(NUMBERS_ONE),    "pqr"},
    {static_cast<uint32_t>(NUMBERS_TWO),    "xyz"},
    {static_cast<uint32_t>(NUMBERS_THREE),  "zzz"}
};

int main()
{
    for (auto it : PersonList)
        std::cout << it.m_id << " : " << it.m_name << "\n";
    return 0;
}

因为我们可以看到上面带有类型转换的 vector 初始化看起来 weird/complex。我怎样才能提高代码的可读性。我试过下面的代码，但它抛出 error: Conversion from 'Numbers' to 'uint32_t' requires a narrow conversion. 任何建议将不胜感激。

/*
struct Person {
    uint32_t        m_id = 0;
    std::string     m_name;

    Person(uint32_t id, std::string name) :
        m_id(static_cast<uint32_t>(id)), m_name(name) {}
};

std::vector<Person> PersonList =
{
    {NUMBERS_ZERO,  "abc"},
    {NUMBERS_ONE,   "pqr"},
    {NUMBERS_TWO,   "xyz"},
    {NUMBERS_THREE, "zzz"}
};
*/

Answer 1

您可以定义一个用于枚举的类型，这样就不需要强制转换了：

enum NUMBERS : uint32_t
{
    NUMBERS_ZERO    = 0xA0000000,
    NUMBERS_ONE     = 0xA0000001,
    NUMBERS_TWO     = 0xA0000002,
    NUMBERS_THREE   = 0xA0000003,
};

如果没有类型定义，可以假定数字是有符号的并且不适合 32 位整数，因此使用缩小转换。

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