std :: vector比普通数组慢得多吗？

我一直认为，这std::vector是“作为数组实现” 的一般常识，等等等等。今天，我进行了测试，但事实并非如此：

以下是一些测试结果：

UseArray completed in 2.619 seconds UseVector completed in 9.284 seconds UseVectorPushBack completed in 14.669 seconds The whole thing completed in 26.591 seconds 大约慢了3到4倍！对于“ vector可能会慢一些纳秒”的注释，并没有真正的理由。

和我使用的代码：

#include #include

#include #include

#include <boost/date_time/posix_time/ptime.hpp> #include <boost/date_time/microsec_time_clock.hpp>

class TestTimer { public: TestTimer(const std::string & name) : name(name), start(boost::date_time::microsec_clockboost::posix_time::ptime::local_time()) { }

    ~TestTimer()
    {
        using namespace std;
        using namespace boost;

        posix_time::ptime now(date_time::microsec_clock<posix_time::ptime>::local_time());
        posix_time::time_duration d = now - start;

        cout << name << " completed in " << d.total_milliseconds() / 1000.0 <<
            " seconds" << endl;
    }

private:
    std::string name;
    boost::posix_time::ptime start;

};

struct Pixel { Pixel() { }

Pixel(unsigned char r, unsigned char g, unsigned char b) : r(r), g(g), b(b)
{
}

unsigned char r, g, b;

};

void UseVector() { TestTimer t("UseVector");

for(int i = 0; i < 1000; ++i)
{
    int dimension = 999;

    std::vector<Pixel> pixels;
    pixels.resize(dimension * dimension);

    for(int i = 0; i < dimension * dimension; ++i)
    {
        pixels[i].r = 255;
        pixels[i].g = 0;
        pixels[i].b = 0;
    }
}

}

void UseVectorPushBack() { TestTimer t("UseVectorPushBack");

for(int i = 0; i < 1000; ++i)
{
    int dimension = 999;

    std::vector<Pixel> pixels;
        pixels.reserve(dimension * dimension);

    for(int i = 0; i < dimension * dimension; ++i)
        pixels.push_back(Pixel(255, 0, 0));
}

}

void UseArray() { TestTimer t("UseArray");

for(int i = 0; i < 1000; ++i)
{
    int dimension = 999;

    Pixel * pixels = (Pixel *)malloc(sizeof(Pixel) * dimension * dimension);

    for(int i = 0 ; i < dimension * dimension; ++i)
    {
        pixels[i].r = 255;
        pixels[i].g = 0;
        pixels[i].b = 0;
    }

    free(pixels);
}

}

int main() { TestTimer t1("The whole thing");

UseArray();
UseVector();
UseVectorPushBack();

return 0;

} 我做错了什么吗？还是我刚刚打破了这个表演神话？

我在Visual Studio 2005中使用发布模式。

在Visual C ++中，#define _SECURE_SCL 0减少UseVector一半（将其减少到4秒）。IMO，这确实是巨大的。