C++ 性能下降(或必须改进代码？)

Question

我正在开发一个简单的程序，它在循环中将相同的字符串复制到另一个字符串中。我使用的是Visual Studio C++ 2019 Community Edition，项目类型为“命令行”。
如果我运行它 3,42 秒，那么计算出的每秒拷贝数是 130 601 397，但如果我运行它 77,97 秒，那么每秒拷贝数是 47 469 296 ...
程序运行的时间越长，性能下降越多......
这是代码:

#include <iostream>
#include <cstdlib>
#include <signal.h>
#include <chrono>
#include <string>

using namespace std;

unsigned long repeats_counter = 0;

std::chrono::steady_clock::time_point t1;
std::chrono::steady_clock::time_point t2;

// When CTRL+C (SIGINT), this is executed 
signal_callback_handler(int signum) {
    t2 = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> diff = t2 - t1;
    std::cout << "Total execution time " << diff.count() << " s\n";
    unsigned long average_repeats_per_sec = (unsigned long)(repeats_counter / diff.count());
    std::cout << "Number of average repeats per second was " << 
    std::to_string(average_repeats_per_sec) << "\n";
    std::cout << "Number of average repeats per minute was " << 
    std::to_string(average_repeats_per_sec * 60) << "\n";
    cout << "Number of effective repeats = " << repeats_counter << endl;
    // Terminate program
    exit(signum);
}


int main()
{
    signal(SIGINT, signal_callback_handler);
    signal(SIGTERM, signal_callback_handler);

    std::string from_str, to_str;

    cout << "Start copying. CTRL+C to stop." << endl;
    t1 = std::chrono::high_resolution_clock::now();
    from_str = "the string to be copied";
    while (true) {
        to_str = from_str;
        repeats_counter++;
    }
    return 0;
}

Answer 1

这可能是由整数溢出引起的。 unsigned long至少是 32 位，在某些平台上它等于 unsigned int. unsigned long long部分缓解了这个问题，但从技术上讲，循环应该有某种防御措施，尽管它增加了循环的成本。
代码可移植性有两个问题，编译器由于实现的原因省略了:

std::chrono::steady_clock::time_point应该是 std::chrono::high_resolution_clock::time_point

signal_callback_handler应该有返回类型 void