C++ std::allocator<T> 与new对比效率使用

基础知识通道: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:分离分配和初始化这两个操作allocator少执行一步,new则一般执行两次(初始化和赋值);

     std::clock_t start = , end = ;

     start = clock();
     std::string *str1 = new std::string[allocate_length];
     auto str6=str1;
     for (int i = ; 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个string原始内存
     auto str4=str3;

     //方法一:使用默认构造
     for (int i = ; i < allocate_length; i++)
     {
         str_allocate.construct(str3++,"Hello World");
     }

     //方法二:使用allocator的伴随算法(分别是带n与不带)
     //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()调用对象的析构，但是内存还是由allocator控制，需要自己释放
     str_allocate.deallocate(str4,allocate_length);
     end = clock();

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

     return ;
 }