Byte/KB/MB/GB 等字节单位换算

字节单位换算公式：

1 GB = 1024 MB
1 MB = 1024 KB
1 KB = 1024 Bytes
1 Byte = 8 bits

将字节单位转化为目标单位

根据公式我写了一段C++代码，用于将输入的以字节为单位的数值，转换为目标单位数值。代码中的枚举类型用的是C++11的语法。

enum class Unit{
    Byte, KB, MB, GB, TB, PB, EB
};

double convert(double size, Unit unit)
{
    double result = size;
    switch (unit)
    {
    case Unit::EB:
        result /= 1024;     // flow through
    case Unit::PB:
        result /= 1024;     // flow through
    case Unit::TB:
        result /= 1024;     // flow through
    case Unit::GB:
        result /= 1024;     // flow through
    case Unit::MB:
        result /= 1024;     // flow through
    case Unit::KB:
        result /= 1024;     // flow through
    case Unit::Byte:
        result /= 1;
    default:
        break;
    }
    return result;
}

测试代码：

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    double size = 2.4 * std::pow(1024, 3);        // 2.4GB
    cout << convert(size, Unit::Byte) << "Byte" << endl;
    cout << convert(size, Unit::KB) << "KB" << endl;
    cout << convert(size, Unit::MB) << "MB" << endl;
    cout << convert(size, Unit::GB) << "GB" << endl;
    cout << convert(size, Unit::TB) << "TB" << endl;
    cout << convert(size, Unit::PB) << "PB" << endl;
    cout << convert(size, Unit::EB) << "EB" << endl;
    return 0;
}

运行结果：

2.57698e+009Byte
2.51658e+006KB
2457.6MB
2.4GB
0.00234375TB
2.28882e-006PB
2.23517e-009EB

将字节单位转化为合适的单位

上面的代码中必须指定目标单位，但很多时候我不知道目标单位，只要转化后的单位看上去比较合理（数值介于1-1024之间）即可，所以又写了下面这段代码，输入以字节为单位的数值，返回一个二元组，该而二元组包含了转换后的大小以及单位。

std::pair<double, Unit> convert(double size)
{
    std::pair<double, Unit> result = std::make_pair(size, Unit::Byte);
    while (result.first >= 1024)
    {
        result.first /= 1024;
        result.second = static_cast<Unit>(1 + static_cast<int>(result.second));
    }
    return result;
}    

测试代码：

    std::pair<double, Unit> result = convert(size);
    cout << result.first;                  // 输出结果： 2.4GB
    switch (result.second)
    {
    case Unit::Byte:
        cout << "Byte" << endl; break;
    case Unit::KB:
        cout << "KB" << endl; break;
    case Unit::MB:
        cout << "MB" << endl; break;
    case Unit::GB:
        cout << "GB" << endl; break;
    case Unit::TB:
        cout << "TB" << endl; break;
    case Unit::PB:
        cout << "PB" << endl; break;
    case Unit::EB:
        cout << "EB" << endl; break;
    default: break;
    }