[C++] Running time and Integer to String

std::string num2str(int64_t p_vint, int8_t p_radix)
{ 
    char str[48] = { 0 };    
    int64_t temp = 0;
    int64_t o_length = 0;
    bool is_negative = false;
    //for hex
    //judge if is negative number
    str[0] = '+';
    if (p_vint < 0)
    {
        str[0] = '-';
        p_vint = 0 - p_vint;
        is_negative = true;
    }

    if (p_radix > 10)
    {
        for (int64_t i = 1; p_vint > 0; ++o_length, ++i)
        {
            temp = p_vint;
            p_vint /= p_radix;
            str[i] = temp - p_vint * p_radix + 0x30;
            str[i] = (str[i] > 0x39 ? (str[i] + 7) : str[i]);
        }
    }
    else
    {
        int a = 0;
        for (int64_t i = 1; p_vint > 0; ++o_length, ++i)
        {
            temp = p_vint;
            p_vint /= p_radix;
            a = temp - p_vint * p_radix + 0x30;
            str[i] = a;
        }
    }

    for (int64_t i = 1; i < (o_length / 2 + 1); i++)
    {
        str[i] ^= str[o_length + 1 - i];
        str[o_length + 1 - i] ^= str[i];
        str[i] ^= str[o_length + 1 - i];
    }

    if (!is_negative)
    {
        str[o_length + 1] = 0;
        char * str_tmp = &str[1];
        return std::string(str_tmp);
    }
    else
    {
        str[++o_length] = 0;
    }
    return std::string(str);
}

　　Running Time:

#include <chrono>
#include <string.h>

using namespace std::chrono;

int main()
{
    auto start = system_clock::now();
    char * str = new char[48];
    memset(str, 0, 48);
    //for (int i = 0; i < 1000000; i++)
    //{
        num2str(6400, 10, str);
        std::cout << str;  
    //}

    auto usage = duration_cast<milliseconds>(system_clock::now() - start);
    std::cout << "Running Time：" << (double)usage.count() << "ms" << std::endl;

    getchar();
    return 0;
}

　　

/*
2.
#include <ctime>

    clock_t start = clock();

    clock_t end = clock();
    std::cout << "Running time:" << (double)(end - start) / CLOCKS_PER_SEC * 1000 << "ms" << std::endl;
*/

　　

//3.No Recommanded:
#include <Windows.h>

int main()
{
    double time = 0;
    double counts = 0;
    LARGE_INTEGER nFreq;
    LARGE_INTEGER nBeginTime;
    LARGE_INTEGER nEndTime;
    QueryPerformanceFrequency(&nFreq);
    QueryPerformanceCounter(&nBeginTime);//开始计时  
    //encode("d:/bgm_.txt", "d:/bgm2.txt");

    //test
    //for (int i = 0; i < 1000000; i++)
    //    int2str(i);   //5.33s
    //for (int i = 0; i < 1000000; i++)
    //    int2str_oss(i);   //23.53s

    QueryPerformanceCounter(&nEndTime);//停止计时  
    time = (double)(nEndTime.QuadPart - nBeginTime.QuadPart) / (double)nFreq.QuadPart;
    std::cout << "Running Time：" << time * 1000 << "ms" << std::endl;

    return 0;