C++ std::allocator 與new對比效率使用

基礎知識通道:http://blog.csdn.net/Xiejingfa/article/details/50955295

 

C/C++:

 

#include <iostream>
#include <vector>
#include <string>

#define allocate_length 100000


int main()
{

    //allocator比new快的原因:分離分配和初始化這兩個操作allocator少執行一步,new則一般執行兩次(初始化和賦值);


    std::clock_t start = 0, end = 0;

    start = clock();
    std::string *str1 = new std::string[allocate_length];
    auto str6=str1;
    for (int i = 0; i < allocate_length; i++)
    {
        *str1++ = "Hello World";
    }

    delete []str6;
    end = clock();
    std::cout << (double(end - start) / CLOCKS_PER_SEC) << std::endl;




    start = clock();
    std::allocator<std::string> str_allocate;
    std::string *str3 = str_allocate.allocate(allocate_length); //分配20個string原始內存
    auto str4=str3;

    //方法一:使用默認構造
    for (int i = 0; i < allocate_length; i++)
    {
        str_allocate.construct(str3++,"Hello World");
    }

    //方法二:使用allocator的伴隨算法(分別是帶n與不帶)
    //其他算法:std::uninitialized_copy(iterator begin,iterator end,T value);

    //std::uninitialized_fill_n(str3,allocate_length,"Hello World");


    //str_allocate.destroy()調用對象的析構，但是內存還是由allocator控制，需要自己釋放
    str_allocate.deallocate(str4,allocate_length);
    end = clock();

    std::cout << (double(end - start) / CLOCKS_PER_SEC) << std::endl;


    return 0;
}