利用C++中union的特性，可以將2個(gè)參數(shù)生成對(duì)應(yīng)類型的唯一key。
如下代碼所示，用2個(gè)short類型的參數(shù)生成一個(gè)int類型的key掏击，當(dāng)param1和param2有一個(gè)不同可以生成唯一的key。
應(yīng)用場(chǎng)景：當(dāng)讀取的配置有一個(gè)index和一個(gè)sub_index,當(dāng)index相同時(shí)sub_index遞增秩铆，此時(shí)我們將index和sub_index組合就可以生成一個(gè)唯一key砚亭，用作存儲(chǔ)配置map的key。
當(dāng)獲取配置的時(shí)侯殴玛，我們可以根據(jù)index和sub_index生成key從map中找到對(duì)應(yīng)配置捅膘。

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int ConvertParamToInt(short param1, short param2)
{
    union 
    {
        int i_value;
        struct 
        {
            short s_value1;
            short s_value2;
        };
    } union_param;
    union_param.s_value1 = param1;
    union_param.s_value2 = param2;
    return union_param.i_value;
}
void ParamIntToValue(const int key, int& param1, int& param2)
{
    union
    {
        int i_value;
        struct
        {
            short s_value1;
            short s_value2;
        };
    } union_param;
    union_param.i_value = key;
    param1 = union_param.s_value1;
    param2 = union_param.s_value2;
}
long long ConvertParamToLongLong(int param1, int param2)
{
    union
    {
        long long ll_value;
        struct
        {
            int i_value1;
            int i_value2;
        };
    } union_param;
    union_param.i_value1 = param1;
    union_param.i_value2 = param2;
    return union_param.ll_value;
}
void ParamLongLongToValue(const long long key, int &param1, int &param2)
{
    union
    {
        long long ll_value;
        struct
        {
            int i_value1;
            int i_value2;
        };
    } union_param;
    union_param.ll_value = key;
    param1 = union_param.i_value1;
    param2 = union_param.i_value2;
}
long long ConvertParamToLongLong(int param1, short param2, short param3)
{
    union
    {
        long long ll_value;
        struct
        {
            int i_value1;
            short s_value2;
            short s_value3;
        };
    } union_param;
    union_param.i_value1 = param1;
    union_param.s_value2 = param2;
    union_param.s_value3 = param3;
    return union_param.ll_value;
}
void ParamLongLongToValue(const long long key, int& param1, short& param2,short &param3)
{
    union
    {
        long long ll_value;
        struct
        {
            int i_value1;
            short s_value2;
            short s_value3;
        };
    } union_param;
    union_param.ll_value = key;
    param1 = union_param.i_value1;
    param2 = union_param.s_value2;
    param3 = union_param.s_value2;
}