C + + std::allocator<t> use

Basic Knowledge Channel:http://blog.csdn.net/Xiejingfa/article/details/50955295

C + +:

1#include <iostream>2#include <vector>3#include <string>4 5 #defineAllocate_length 1000006 7 8 intMain ()9 {Ten  One     //allocator faster than NEW: Split allocation and initialization these two operations allocator one less step, new is typically performed two times (initialization and assignment); A  -  -std::clock_t start =0, end =0; the  -Start =clock (); -STD::string*STR1 =NewSTD::string[allocate_length]; -Auto str6=str1; +      for(inti =0; i < allocate_length; i++) -     { +*str1++ ="Hello World"; A     } at  -     Delete[]STR6; -End =clock (); -Std::cout << (Double(End-start)/clocks_per_sec) <<Std::endl; -  -  in  -  toStart =clock (); +STD::ALLOCATOR&LT;STD::string>str_allocate; -STD::string*STR3 = Str_allocate.allocate (allocate_length);//allocate 20 strings of raw memory theAuto str4=STR3; *  $     //method One: Use the default constructPanax Notoginseng      for(inti =0; i < allocate_length; i++) -     { theStr_allocate.construct (str3++,"Hello World"); +     } A  the     //method Two: The adjoint algorithm using allocator (with N and no band respectively) +     //Other algorithms: std::uninitialized_copy (iterator begin,iterator end,t value); -  $     //Std::uninitialized_fill_n (str3,allocate_length, "Hello World"); $  -  -     //Str_allocate.destroy () calls the destructor of the object, but the memory is still controlled by allocator and needs to be freed the str_allocate.deallocate (str4,allocate_length); -End =clock ();Wuyi  theStd::cout << (Double(End-start)/clocks_per_sec) <<Std::endl; -  Wu  -     return 0; About}

C + + std::allocator<t> use