转换字节顺序

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从PostgreSQL传来的二进制数据是网络字节顺序的,即高位先到,低位后到.
使用时转换成本机字节顺序, 才能万无一失.

//将网络字节序的字节数据,转换成本机字节顺序的:
long long netToHost_Int8(byte * bytes, int len = 8)
{
    unsigned long long llv = 0;

    for (int i = 0; i < len; i++){
        llv <<= 8;
        llv |= bytes[i];
    }

    return llv;
}

double netToHost_Double(char * chars)
{
    unsigned long long llv = netToHost_Int8((byte*)chars);
    return *(double*)&llv;
}

int netToHost_Int4(char * chars)
{
    return (int)netToHost_Int8((byte*)chars, 4);
}

short netToHost_Int2(char * chars)
{
    return (short)netToHost_Int8((byte*)chars, 2);
}