CONTENTS
备注:
本读书笔记基于侯捷先生的《STL源码剖析》,截图和注释版权均属于原作者所有。
本读书笔记中的源码部分直接拷贝自SGI-STL,部分代码删除了头部的版权注释,但代码版权属于原作者。
小弟初看stl,很多代码都不是太懂,注释可能有很多错误,还请路过的各位大牛多多给予指导。
为了降低学习难度,作者这里换到了SGI-STL-2.91.57的源码来学习,代码下载地址为【 http://jjhou.boolan.com/jjwbooks-tass.htm 】
stl_vector.h:
部分代码如下,去掉了文件头部的注释。
//默认使用alloc作为空间构造器,其实就是new,delete。 template <class T, class Alloc = alloc> class vector { public: //由于vector在内存中的排放类似于数组,因此迭代器,引用均可以直接使用vector存储的类型。 typedef T value_type; typedef value_type* pointer; typedef const value_type* const_pointer; typedef value_type* iterator; typedef const value_type* const_iterator; typedef value_type& reference; typedef const value_type& const_reference; typedef size_t size_type; typedef ptrdiff_t difference_type; #ifdef __STL_CLASS_PARTIAL_SPECIALIZATION typedef reverse_iterator<const_iterator> const_reverse_iterator; typedef reverse_iterator<iterator> reverse_iterator; #else /* __STL_CLASS_PARTIAL_SPECIALIZATION */ typedef reverse_iterator<const_iterator, value_type, const_reference, difference_type> const_reverse_iterator; typedef reverse_iterator<iterator, value_type, reference, difference_type> reverse_iterator; #endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */ protected: typedef simple_alloc<value_type, Alloc> data_allocator; iterator start;//起始内容指针 iterator finish;//终止内容指针 iterator end_of_storage;//存储空间的最后位置指针 void insert_aux(iterator position, const T& x); void deallocate() { //当空间被销毁时,从起始点开始销毁,销毁个数为存储空间个数。 if (start) data_allocator::deallocate(start, end_of_storage - start); } //申请一块可以容纳n个T的空间,然后全部赋值为value void fill_initialize(size_type n, const T& value) { start = allocate_and_fill(n, value);//内存申请好之后,起始地址就是起始内容指针 finish = start + n;//终止内容指针为起始指针 + n (可以参考数组) end_of_storage = finish;//由于空间是刚刚申请的,因此空间的最后位置就是终止内容的位置 } public: //以下为各种get操作,返回的是起始位置,终止位置,以及空间个数 iterator begin() { return start; } const_iterator begin() const { return start; } iterator end() { return finish; } const_iterator end() const { return finish; } reverse_iterator rbegin() { return reverse_iterator(end()); } const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); } reverse_iterator rend() { return reverse_iterator(begin()); } const_reverse_iterator rend() const { return const_reverse_iterator(begin()); } //返回当前已经存储的空间的数目 size_type size() const { return size_type(end() - begin()); } //由于vector的空间是动态扩充的,因此不存在最大值,这里就将最大值设为当 //全部内存耗尽时,能存储的空间数目 size_type max_size() const { return size_type(-1) / sizeof(T); } //返回当前容量,由于vector动态扩充时会多申请一部分内存,因此这里需要使用存储空间的最后位置来 //计算 size_type capacity() const { return size_type(end_of_storage - begin()); } bool empty() const { return begin() == end(); } //vector在内存中是连续存放的,因此可以通过内存操作获取指定位置的内容 reference operator[](size_type n) { return *(begin() + n); } const_reference operator[](size_type n) const { return *(begin() + n); } //构造函数,初始化时,起始点=终止点=存储空间最后点=0,此时并不分配内存 vector() : start(0), finish(0), end_of_storage(0) {} //构造函数,构造后就有n个T,每个T都被赋值为value,因此这里调用了fill_initialize vector(size_type n, const T& value) { fill_initialize(n, value); } vector(int n, const T& value) { fill_initialize(n, value); } vector(long n, const T& value) { fill_initialize(n, value); } explicit vector(size_type n) { fill_initialize(n, T()); } //拷贝构造函数,直接将原vector(即x)的有效内容拷贝过来 vector(const vector<T, Alloc>& x) { start = allocate_and_copy(x.end() - x.begin(), x.begin(), x.end()); finish = start + (x.end() - x.begin()); end_of_storage = finish; } #ifdef __STL_MEMBER_TEMPLATES template <class InputIterator> vector(InputIterator first, InputIterator last) : start(0), finish(0), end_of_storage(0) { range_initialize(first, last, iterator_category(first)); } #else /* __STL_MEMBER_TEMPLATES */ vector(const_iterator first, const_iterator last) { size_type n = 0; distance(first, last, n); start = allocate_and_copy(n, first, last); finish = start + n; end_of_storage = finish; } #endif /* __STL_MEMBER_TEMPLATES */ ~vector() { destroy(start, finish); deallocate(); } vector<T, Alloc>& operator=(const vector<T, Alloc>& x); //扩充容量至n,如果当前容量>n了,那么什么也不做 void reserve(size_type n) { if (capacity() < n) { //当前容量<n时 const size_type old_size = size(); //先申请一块新的内存,容量为n,然后将当前的有效数据拷贝过去 iterator tmp = allocate_and_copy(n, start, finish); //将原有的内存上的有效数据销毁(调用析构函数) destroy(start, finish); //释放原有内存 deallocate(); //将start,finish,end_of_storage赋值为新内存的值 start = tmp; finish = tmp + old_size; end_of_storage = start + n; } } //返回第一个和最后一个有效数据的引用,这里注意的是finish指向的是 //最后的有效数据的下一个,因此返回最后一个有效数据时,finish需要 -1 reference front() { return *begin(); } const_reference front() const { return *begin(); } reference back() { return *(end() - 1); } const_reference back() const { return *(end() - 1); } //在vector的最后在添加一个T,内容为x void push_back(const T& x) { //如果终止内容指针 != 存储空间最后指针,说明之前申请的内存还没有用完, //因此可以直接在终止内容指针上进行赋值,然后终止内容指针向前 + 1 if (finish != end_of_storage) { construct(finish, x); ++finish; } else //如果终止内容指针=存储空间最后指针,那么说明之前申请的内存已经用完了, //根据vector的内存策略,必须重新申请内存。 insert_aux(end(), x); } void swap(vector<T, Alloc>& x) { __STD::swap(start, x.start); __STD::swap(finish, x.finish); __STD::swap(end_of_storage, x.end_of_storage); } //在指定位置上插入一个T,内容为x iterator insert(iterator position, const T& x) { size_type n = position - begin(); //首先判断这个指定位置是不是终止内容指针,如果是终止内容指针,而且之前申请的内存还没有用完, //就直接在终止内容指针上进行赋值,然后终止内容指针向前 + 1 if (finish != end_of_storage && position == end()) { construct(finish, x); ++finish; } else //如果当前的位置不是最后的位置,或者内存用完了,就只能重新申请内存。 insert_aux(position, x); //返回插入的位置 return begin() + n; } iterator insert(iterator position) { return insert(position, T()); } #ifdef __STL_MEMBER_TEMPLATES template <class InputIterator> void insert(iterator position, InputIterator first, InputIterator last) { range_insert(position, first, last, iterator_category(first)); } #else /* __STL_MEMBER_TEMPLATES */ void insert(iterator position, const_iterator first, const_iterator last); #endif /* __STL_MEMBER_TEMPLATES */ void insert (iterator pos, size_type n, const T& x); void insert (iterator pos, int n, const T& x) { insert(pos, (size_type) n, x); } void insert (iterator pos, long n, const T& x) { insert(pos, (size_type) n, x); } //从最后边删除一个T,这里仅仅调用析构函数,并不释放内存 void pop_back() { --finish; destroy(finish); } //在指定位置删除一个T iterator erase(iterator position) { //如果要删除的T不是在最后,那么需要将其后面的所有内容全部向前复制一个,这里 //使用的是copy函数,copy函数会将要覆盖的内容先销毁掉,然后把新的内容复制过去 if (position + 1 != end()) copy(position + 1, finish, position); //当copy调用完成后,最后的那个有效数据就有两份了(一份是之前存在的,一份是刚刚拷贝的) //那么这里就需要把最后边的那个之前存在的给销毁,顺便更新指针。 --finish; destroy(finish); return position; } //删除指定位置区间的所有元素 iterator erase(iterator first, iterator last) { //这里使用的是copy函数,后面笔记 iterator i = copy(last, finish, first); destroy(i, finish); finish = finish - (last - first); return first; } //重新设置vector的大小 //如果当前有效数据的数目>新设置的数目,那么多出来的数据会被删除 //如果当前有效数据的数目<新设置的数目,那么就在vector的尾部添加元素,并赋值为x void resize(size_type new_size, const T& x) { if (new_size < size()) erase(begin() + new_size, end()); else insert(end(), new_size - size(), x); } void resize(size_type new_size) { resize(new_size, T()); } void clear() { erase(begin(), end()); } protected: //申请一块能容纳n个T的内存,然后每个T都赋值为x iterator allocate_and_fill(size_type n, const T& x) { //申请内存 iterator result = data_allocator::allocate(n); __STL_TRY { //调用拷贝构造函数 uninitialized_fill_n(result, n, x); return result; } __STL_UNWIND(data_allocator::deallocate(result, n)); } #ifdef __STL_MEMBER_TEMPLATES template <class ForwardIterator> iterator allocate_and_copy(size_type n, ForwardIterator first, ForwardIterator last) { iterator result = data_allocator::allocate(n); __STL_TRY { uninitialized_copy(first, last, result); return result; } __STL_UNWIND(data_allocator::deallocate(result, n)); } #else /* __STL_MEMBER_TEMPLATES */ iterator allocate_and_copy(size_type n, const_iterator first, const_iterator last) { iterator result = data_allocator::allocate(n); __STL_TRY { uninitialized_copy(first, last, result); return result; } __STL_UNWIND(data_allocator::deallocate(result, n)); } #endif /* __STL_MEMBER_TEMPLATES */ #ifdef __STL_MEMBER_TEMPLATES template <class InputIterator> void range_initialize(InputIterator first, InputIterator last, input_iterator_tag) { for ( ; first != last; ++first) push_back(*first); } // This function is only called by the constructor. We have to worry // about resource leaks, but not about maintaining invariants. template <class ForwardIterator> void range_initialize(ForwardIterator first, ForwardIterator last, forward_iterator_tag) { size_type n = 0; distance(first, last, n); start = allocate_and_copy(n, first, last); finish = start + n; end_of_storage = finish; } template <class InputIterator> void range_insert(iterator pos, InputIterator first, InputIterator last, input_iterator_tag); template <class ForwardIterator> void range_insert(iterator pos, ForwardIterator first, ForwardIterator last, forward_iterator_tag); #endif /* __STL_MEMBER_TEMPLATES */ }; template <class T, class Alloc> //判断两个vector是否相等,判断里面的每个数据是否相同 inline bool operator==(const vector<T, Alloc>& x, const vector<T, Alloc>& y) { return x.size() == y.size() && equal(x.begin(), x.end(), y.begin()); } template <class T, class Alloc> inline bool operator<(const vector<T, Alloc>& x, const vector<T, Alloc>& y) { return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end()); } #ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER template <class T, class Alloc> inline void swap(vector<T, Alloc>& x, vector<T, Alloc>& y) { x.swap(y); } #endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */ //vector的赋值构造函数 template <class T, class Alloc> vector<T, Alloc>& vector<T, Alloc>::operator=(const vector<T, Alloc>& x) { if (&x != this) { //如果x的有效元素的个数大于当前的容量, //那就只能先申请一块新的内存,用来存放x的所有数据, //然后释放掉本地的空间 if (x.size() > capacity()) { iterator tmp = allocate_and_copy(x.end() - x.begin(), x.begin(), x.end()); destroy(start, finish); deallocate(); start = tmp; end_of_storage = start + (x.end() - x.begin()); } //如果当前的有效数据个数>x,那么就将x的所有数据复制到本地,覆盖本地已有的数据 //然后销毁掉本地的剩余有效数据 else if (size() >= x.size()) { iterator i = copy(x.begin(), x.end(), begin()); destroy(i, finish); } //如果当前的有效数据个数<x,但是本地有足够的存储空间,那么就将x的所有数据复制到本地,覆盖本地已有的数据 else { copy(x.begin(), x.begin() + size(), start); uninitialized_copy(x.begin() + size(), x.end(), finish); } finish = start + x.size(); } return *this; } template <class T, class Alloc> //在指定位置插入一个T, void vector<T, Alloc>::insert_aux(iterator position, const T& x) { //如果finish != end_of_storage,说明本地至少还有一个未使用的内存空间 if (finish != end_of_storage) { //先把vector的最后面的那个有效数据重新构造一个,放到最后。,这里主要是为了满足 //copy_backward的调用条件 construct(finish, *(finish - 1)); ++finish; T x_copy = x; //将position后的所有有效数据(除了最后的那个刚刚构造出来的)全部向后复制一个位置 copy_backward(position, finish - 2, finish - 1); //然后将空出来的position的内存赋值为x,这里会调用到T的拷贝构造函数 *position = x_copy; } else { //当本地没有可用的内存空间时,需要申请一份新的内存,这里采取的策略是申请一块原有内存的2倍大的内存 const size_type old_size = size(); const size_type len = old_size != 0 ? 2 * old_size : 1; //申请内存 iterator new_start = data_allocator::allocate(len); iterator new_finish = new_start; __STL_TRY { //先将 position 之前的数据拷贝到新的内存空间里 new_finish = uninitialized_copy(start, position, new_start); //然后在position位置上使用x构造新的数据 construct(new_finish, x); ++new_finish; //最后将position之后的数据拷贝到新的内存空间中 new_finish = uninitialized_copy(position, finish, new_finish); } # ifdef __STL_USE_EXCEPTIONS catch(...) { //出异常了!! //将拷贝的数据全部销毁掉 destroy(new_start, new_finish); //将新申请的内存释放掉 data_allocator::deallocate(new_start, len); //把异常扔出去 throw; } # endif /* __STL_USE_EXCEPTIONS */ //将原有的数据销毁掉 destroy(begin(), end()); //将原有的内存释放掉 deallocate(); //根据新的内存更新指针 start = new_start; finish = new_finish; end_of_storage = new_start + len; } } template <class T, class Alloc> //和上面的insert_aux函数差不多 void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) { if (n != 0) { //如果剩余的未使用的内存数量>=n,说明不需要重新申请新的内存 if (size_type(end_of_storage - finish) >= n) { T x_copy = x; const size_type elems_after = finish - position; iterator old_finish = finish; if (elems_after > n) { uninitialized_copy(finish - n, finish, finish); finish += n; copy_backward(position, old_finish - n, old_finish); fill(position, position + n, x_copy); } else { uninitialized_fill_n(finish, n - elems_after, x_copy); finish += n - elems_after; uninitialized_copy(position, old_finish, finish); finish += elems_after; fill(position, old_finish, x_copy); } } else { const size_type old_size = size(); const size_type len = old_size + max(old_size, n); iterator new_start = data_allocator::allocate(len); iterator new_finish = new_start; __STL_TRY { new_finish = uninitialized_copy(start, position, new_start); new_finish = uninitialized_fill_n(new_finish, n, x); new_finish = uninitialized_copy(position, finish, new_finish); } # ifdef __STL_USE_EXCEPTIONS catch(...) { destroy(new_start, new_finish); data_allocator::deallocate(new_start, len); throw; } # endif /* __STL_USE_EXCEPTIONS */ destroy(start, finish); deallocate(); start = new_start; finish = new_finish; end_of_storage = new_start + len; } } } #ifdef __STL_MEMBER_TEMPLATES template <class T, class Alloc> template <class InputIterator> void vector<T, Alloc>::range_insert(iterator pos, InputIterator first, InputIterator last, input_iterator_tag) { for ( ; first != last; ++first) { pos = insert(pos, *first); ++pos; } } template <class T, class Alloc> template <class ForwardIterator> void vector<T, Alloc>::range_insert(iterator position, ForwardIterator first, ForwardIterator last, forward_iterator_tag) { if (first != last) { size_type n = 0; distance(first, last, n); if (size_type(end_of_storage - finish) >= n) { const size_type elems_after = finish - position; iterator old_finish = finish; if (elems_after > n) { uninitialized_copy(finish - n, finish, finish); finish += n; copy_backward(position, old_finish - n, old_finish); copy(first, last, position); } else { ForwardIterator mid = first; advance(mid, elems_after); uninitialized_copy(mid, last, finish); finish += n - elems_after; uninitialized_copy(position, old_finish, finish); finish += elems_after; copy(first, mid, position); } } else { const size_type old_size = size(); const size_type len = old_size + max(old_size, n); iterator new_start = data_allocator::allocate(len); iterator new_finish = new_start; __STL_TRY { new_finish = uninitialized_copy(start, position, new_start); new_finish = uninitialized_copy(first, last, new_finish); new_finish = uninitialized_copy(position, finish, new_finish); } # ifdef __STL_USE_EXCEPTIONS catch(...) { destroy(new_start, new_finish); data_allocator::deallocate(new_start, len); throw; } # endif /* __STL_USE_EXCEPTIONS */ destroy(start, finish); deallocate(); start = new_start; finish = new_finish; end_of_storage = new_start + len; } } } #else /* __STL_MEMBER_TEMPLATES */ template <class T, class Alloc> void vector<T, Alloc>::insert(iterator position, const_iterator first, const_iterator last) { if (first != last) { size_type n = 0; distance(first, last, n); if (size_type(end_of_storage - finish) >= n) { const size_type elems_after = finish - position; iterator old_finish = finish; if (elems_after > n) { uninitialized_copy(finish - n, finish, finish); finish += n; copy_backward(position, old_finish - n, old_finish); copy(first, last, position); } else { uninitialized_copy(first + elems_after, last, finish); finish += n - elems_after; uninitialized_copy(position, old_finish, finish); finish += elems_after; copy(first, first + elems_after, position); } } else { const size_type old_size = size(); const size_type len = old_size + max(old_size, n); iterator new_start = data_allocator::allocate(len); iterator new_finish = new_start; __STL_TRY { new_finish = uninitialized_copy(start, position, new_start); new_finish = uninitialized_copy(first, last, new_finish); new_finish = uninitialized_copy(position, finish, new_finish); } # ifdef __STL_USE_EXCEPTIONS catch(...) { destroy(new_start, new_finish); data_allocator::deallocate(new_start, len); throw; } # endif /* __STL_USE_EXCEPTIONS */ destroy(start, finish); deallocate(); start = new_start; finish = new_finish; end_of_storage = new_start + len; } } }
备注:
关于 copy 和 copy_backward,个人的总结如下,不知道对不对。
如果是简单类型或者存储内容不复杂(拷贝,赋值等简单),那么stl底层copy会直接调用memmove,上层vector代码也不用担心析构函数的处理。
如果存储内容类比较复杂,这里stl底层copy会循环进行赋值操作,不会调用析构函数,此时类内部资源的释放就需要依靠赋值构造函数来处理。
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