C++ std::allocator<T>使用

             1 #include <iostream>
 2 #include <vector>
 3 #include <string>
 4 5#define allocate_length 100000
 6 7 8int main()
 9{
1011//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);121314     std::clock_t start = 0, end = 0;
1516     start = clock();
17     std::string *str1 = new std::string[allocate_length];
18     auto str6=str1;
19for (int i = 0; i < allocate_length; i++)
20    {
21         *str1++ = "Hello World";
22    }
2324delete []str6;
25     end = clock();
26     std::cout << (double(end - start) / CLOCKS_PER_SEC) << std::endl;
2728293031     start = clock();
32     std::allocator<std::string> str_allocate;
33     std::string *str3 = str_allocate.allocate(allocate_length); //分配20个string原始内存34     auto str4=str3;
3536//方法一:使用默认构造37for (int i = 0; i < allocate_length; i++)
38    {
39         str_allocate.construct(str3++,"Hello World");
40    }
4142//方法二:使用allocator的伴随算法(分别是带n与不带)
43//其他算法:std::uninitialized_copy(iterator begin,iterator end,T value);
4445//std::uninitialized_fill_n(str3,allocate_length,"Hello World");
464748//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49    str_allocate.deallocate(str4,allocate_length);
50     end = clock();
5152     std::cout << (double(end - start) / CLOCKS_PER_SEC) << std::endl;
535455return0;
56 }