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迭代器失效
这篇文章是基于上一篇的Vector的模拟实现的补充知识点,首先我们需要重点关注的便是迭代器失效的问题。
void test_vector3()
{
std::vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
std::vector<int>::iterator it = v1.begin();
while (it != v1.end())
{
if (*it % 2 == 0)
{
v1.erase(it);
}
else
{
++it;
}
}
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}
我们可以看这个erase功能的实现部分
void erase(iterator pos)
{
assert(pos >= _start);
assert(pos < _finish);
iterator it = pos + 1;
while (it != _finish)
{
*(it - 1) = *it;
++it;
}
--_finish;
}
其实我们可以分析出来迭代器失效的原因,其原因在于当删除it指示的元素的时候,it未能被重新赋值,it位置后面的数值赋值到了it位置,内存空间位置被改变,从而造成迭代器失效。
而解决迭代器失效的方法就是重新更新迭代器。
void test_vector3()
{
std::vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
std::vector<int>::iterator it = v1.begin();
while (it != v1.end())
{
if (*it % 2 == 0)
{
it=v1.erase(it);
}
else
{
++it;
}
}
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}
比如说在这段代码当中,我们对迭代器进行重新更新,从而保证了它的时效性。
构造函数的使用
void test_vector5()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
vector<int> v2(v1);
for (auto e : v2)
{
cout << e << " ";
}
cout << endl;
vector<int> v3;
v3.push_back(10);
v3.push_back(20);
v3.push_back(30);
v1 = v3;
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}
void test_vector6()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
vector<int> v2(v1.begin() + 1, v1.end());
for (auto e : v2)
{
cout << e << " ";
}
cout << endl;
string s("hello");
vector<int> v3(s.begin(), s.end());
for (auto e : v3)
{
cout << e << " ";
}
cout << endl;
list<int> lt;
lt.push_back(100);
lt.push_back(100);
lt.push_back(100);
vector<int> v4(lt.begin(), lt.end());
for (auto e : v4)
{
cout << e << " ";
}
cout << endl;
}
所以说,其实Vector的兼容性蛮强大的,任何类型的数据都能放在vector中
void test_vector7()
{
int i = 0;
int j(1);
int k = int();
int x = int(2);
vector<string>v1(10);
vector<string> v2(10, "xxx");
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
for (auto e : v2)
{
cout << e << " ";
}
cout << endl;
vector <int> v3(10, 1);
for (auto e : v3)
{
cout << e << " ";
}
cout << endl;
vector<int> v4(10, 1);
for (auto e : v4)
{
cout << e << " ";
}
cout << endl;
}
构造:
A aa1(1, 1);
A aa2 = { 2,2 };
A aa9{ 2,2 };
const A& aa8 = { 1,1 };
A aa3(1);
A aa4 = 1;
A aa5(1);
A aa6 = { 1 };
A aa7{ 1 };
隐式类型转换
vector<int> v1({ 1,2,3,4,5,6 });
vector<int> v2 = { 10,20,30 };
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
auto il1 = { 1,2,3,4,5,6 };
initializer_list<int> il2 = { 1,2,3,4,5,6 };
cout << typeid(il1).name() << endl;
cout << sizeof(il2) << endl;
for (auto e : il1)
{
cout << e << " ";
}
cout << endl;
initializer_list是一个代理对象,它就是auto的类型,它的大小就是两个指针的大小(一个指向数量的指针,一个指向存储元素的数组)
void test_vector9()
{
vector<string> v1;
v1.push_back("1111111111111111");
v1.push_back("1111111111111111");
v1.push_back("1111111111111111");
v1.push_back("1111111111111111");
v1.push_back("1111111111111111");
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}