C + + Primer The 18th chapter Vector's re-implementation and bug correction

C++primer 18th. 1.2 In introducing the allocator class, an example of a vector modeled in the standard library was given. Feel the sample code is very good, but I found a bug, shared with everyone.

According to the author's sample program, compile the program always in the Alloc.construct () function error, different IDE may be prompted by different reasons, I am undefined reference to ' vector<std::string>: Alloc '.

Think about it, it should be related to the static property of the Alloc member in the class vector, so there are two ways to fix it:

1) Delete the static keyword

2) Add:template<class t> std::allocator<t> in global scope vector<t>::alloc;

The test source code is as follows:

1#include <iostream>2#include <string>3#include <memory>4 using namespacestd;5 6 std::p trdiff_t MAX (std::p trdiff_t A, std::p trdiff_t B)7 {8     returna > B?a:b;9 }Ten  OneTemplate <classT>classvector{ A  Public: -Vector (): Elements (0), First_free (0), End (0) {} -     voidPush_back (Constt&); the  - Private: -     StaticStd::allocator<t>Alloc; -     voidreallocate (); +  Public: -Telements; +TFirst_free; ATend; at }; -  -template<classT> std::allocator<t> vector<t>::alloc;//If there is no such sentence, the compiler error, but if the class vector to remove the static keyword, this sentence can be deleted -  -Template <classT> - voidVector<t>::p Ush_back (Constt&t) in { -     if(First_free = =end) to reallocate (); + alloc.construct (first_free,t); -++First_free; the } *  $Template <classT>Panax Notoginseng voidVector<t>:: Reallocate () - { thestd::p trdiff_t size = first_free-elements; +std::p trdiff_t newcapacity =2* MAX (size,1); A  theT * newelements =alloc.allocate (newcapacity); +  - uninitialized_copy (Elements, First_free, newelements); $  $      for(T * p = first_free; p! = elements; Alloc.destroy (--p)); -  -     if(elements) theAlloc.deallocate (Elements, End-elements); - Wuyielements =newelements; theFirst_free = elements +size; -End = elements +newcapacity; Wu } -  About intMain () $ { -vector<string>str; -     strings; -      for(inti =0; I <5; ++i) A     { +Cin>>s; the Str.push_back (s); -     } $      for(string* p = str.elements; P! = Str.first_free; ++p) thecout<<*p<<Endl; the     return 0; the}

Although know the solution, but for the cause of the bug is not very clear, welcome to message exchange and advice.

C + + Primer The 18th chapter Vector's re-implementation and bug correction