c++(模板类)实现顺序表

#pragma once
#include <iostream>
#include <string>
#include <assert.h>
using namespace std;
template<typename T>
class SeqList
{
public:
SeqList()
:_a(NULL)
,_capacity(0)
,_size(0)
{}

SeqList(const SeqList<T>& s)
:_size(s._size)
,_capacity(s._capacity)
,_a(new T[s._capacity])
{
for (size_t i=0;i<_capacity;i++)
{
_a[i]=s._a[i];
}
}
SeqList<T>& operator= (SeqList<T> s)
{
if(this!=&s)
{
delete _a;
_a=new T[s._capacity];
for (size_t i=0;i<s._size;i++)
{
_a[i]=s._a[i];
}
_capacity=s._capacity;
_size=s._size;}

return *this;
}
~SeqList()
{
if (_a)
{
delete[] _a;
//free(_a);
_size = _capacity = 0;
_a=NULL;
}

}

void PushBack(const T& x)
{
_CheckCapacity();

_a[_size] = x; //?
++_size;
}

void PopBack()
{
if(_size > 0)
--_size;
}

T& Back()
{
assert(_size > 0);
return _a[_size-1];
}
size_t Size()
{
return _size;
}

bool Empty()
{
return _size == 0;
}
void PushFront(const T& x)
{
_CheckCapacity();
size_t end= _size;
while (end-->=1)
{
_a[end+1]=_a[end];
}
_a[0]=x;
++_size;
}
void popFront()
{
if (_size==0)
{
return;
}
else	if(_size > 0)
{
--_size;
_a[_size]=_a[_size+1];
}

}

void    Print()
{
for (size_t i = 0; i < _size; ++i)
{
cout<<_a[i]<<" ";
}
cout<<endl;
}

protected:
void _CheckCapacity()
{
if (_size >= _capacity)
{

_capacity = _capacity*2+3;
T* tmp = new T[_capacity];
if (_a)
{
// 优化
//memcpy(tmp, _a, sizeof(T)*_size);    //若模板类是内置类型或string字符串小于16时使用memcpy完全可以，
//但是当字符串大于15时，这种方式就会出现问题，因为此时的数据
//就不是存放于buf中了，而是用ptr指针指向一个空间保存数据，
//因为memcpy是值拷贝，所以现在会将ptr的地址拷到新的ptr空间，
//此时是两个指针指向同一块空间，拷贝完成后将就得空间释放时，
//新的ptr就变成了野指针，所以程序崩溃。
for (size_t i = 0; i < _size; ++i)
{
tmp[i] = _a[i];
}
delete[] _a;
}

_a = tmp;
}
}

protected:
T* _a;
size_t _size;
size_t _capacity;
};
// Push / Pop
void TestSeqList1()
{
SeqList<int> s1;
s1.PushBack(1);
s1.PushBack(2);
s1.PushBack(3);
s1.PushBack(4);

s1.Print();

s1.PopBack();
s1.PopBack();
s1.PopBack();
s1.PopBack();
s1.PopBack();
s1.Print();
}
// 拷贝、复制运算符的重载
void TestSeqList2()
{
SeqList<int> s1;
s1.PushBack(1);
s1.PushBack(2);
s1.PushBack(3);
s1.PushBack(4);
s1.Print();

SeqList<int> s2(s1);
s2.Print();

SeqList<int> s3;

s3 = s2;
s3.Print();
}

void TestSeqList3()
{
// 深层次的深浅拷贝
SeqList<string> s1;
s1.PushBack("11111");
s1.PushBack("222222222");
s1.PushBack("33");
s1.PushBack("4444444444444444444444444444444444444444444444 ");
s1.PushBack("33");
s1.PushBack("33");
s1.PushBack("33");
s1.PushBack("33");
s1.PushBack("33");

s1.PushBack("33");

s1.Print();
}
void TestSeqList4()
{
SeqList< int> s4;
s4.PushFront(1);
s4.PushFront(1);
s4.popFront();
s4.popFront();
s4.popFront();
s4.Print();
}