vector源码3(参考STL源码--侯捷):pop_back、erase、clear、insert

pop_back

//删除尾部元素，调整大小
void pop_back(){
    --finish; //尾端标记往前一格，表示放弃尾部元素
    destroy(finish); 
}

erase

//清除(first,last)中的所有元素
iterator erase(iterator first,iterator last){
    iterator i=copy(last,finish,first);//将last到finish的元素往前复制，从first位置开始
    destory(i,finish);
    finish=finish-(last-first);
    return first;
}
//清除某个位置上的元素
iterator erase(iterator position){
    if(position+1!=end()){
        copy(position+1,finish,position);
    }
    --finish;
    destory(finish);
    return position;
}

clear

void clear(){
    erase(begin(),end());
}

insert

template <class T,class Alloc>
void vector<T,Alloc>::insert(iterator position,size_type n,const T& x){
    if(n!=0){
        if(size_type(end_of_storage-finish)>=n){
            //备用空间大于等于"新增元素"
            T x_copy=x;
            //以下计算插入点之后的现有元素个数
            const size_type elems_after=finish-position;
            iterator old_finish=finish;
            if(elems_after>n){
                //(1)、"插入点之后的现有元素个数"大于"新增元素个数"(见图1)
                //①从finish处开始复制范围(finish-n,finish)的元素
                uninitialized_copy(finish-n,finish,finish);
                finish+=n; //②vector尾部后移
                //③将范围(position,old_finish-n)的元素移到(,old_finish)处
                copy_backward(position,old_finish-n,old_finish);
                //④从插入点开始填入元素
                fill(position,position+n,x_copy);
            }
            else{
                //(2)、"插入点之后的现有元素个数"小于"新增元素个数"（见图2）
                //①从finish处复制n-elems_after个元素x_copy
                uninitialized_fill_n(finish,n-elems_after,x_copy);
                finish+=n-elems_after; //②vector尾部后移
                //③从finish处开始复制范围(position,old_finish)的元素
                uninitialized_copy(position,old_finish,finish);
                finish+=elems_after; //④vector尾部后移
                //⑤从插入点开始填入元素
                fill(position,old_finish,x_copy);
            }
        }
        else{
            //备用空间大于等于"新增元素",即必须配置额外空间
            //首先决定新长度，旧长度的两倍，或者旧长度+新长度（见图3）
            const size_type old_size=size();
            const size_type len=old_size+max(old_size,n);
            //以下配置新的vector空间
            iterator new_start=data_allocator::allocate(len);
            iterator new_finish=new_start;
            __STL_TRY{
                //①先将旧的vector的插入点之前的元素复制到新的空间
                new_finish=uninitialized_copy(start,position,new_start);
                //②再将新增的元素填入新空间
                new_finish=uninitialized_fill_n(new_finish,n,x);
                //③再将旧vector的插入点之后的元素复制到新空间
                new_finish=uninitialized_copy(position,finish,new_finish);
            }
#ifdef __STL_USE_EXCEPTIONS
            catch(...){
                //如果发现异常，实现rollback
                destory(new_start,new_finish);
                data_allocator::deallocate(new_satrt,len);
                throw;
            }
#endif /*__STL_USE_EXCEPTIONS*/
            //以下清除并释放旧的vector
            destory(start,finish);
            deallocate();
            //调整水位标记
            start=new_start;
            finish=new_finish;
            end_of_storage=new_start+len;
            }
        }
    }
}

图1

图2

图3