在之前已经介绍了string类 【C++】string类初步介绍和【C++】string进一步介绍,这次来看看C++中的顺序表vector。
构造
构造有: vector<int> v;
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
for (size_t i = 0; i < v.size(); i++)
{
cout << v[i] << " ";
}
cout << endl;
还有在构造的时候直接赋值vector<int>v(10, 1);
构造一个int类型的顺序表开了10个空间,这10个空间初始化为1:
resize开一个空间,空间开好了以后,进行填值初始化。
举个例子:开10个空间,然后初始化为0:
vector<int> a;
a.resize(10, 0);
for (auto e : a)
{
cout << e << " ";
}
cout << endl;
来看看vector的扩容机制:
void test_vector2()
{
size_t sz;
vector<int> v;
sz = v.capacity();
cout << "making v grow:\n";
for (int i = 0; i < 100; ++i)
{
v.push_back(i);
if (sz != v.capacity())
{
sz = v.capacity();
cout << "capacity changed: " << sz << '\n';
}
}
}
这里是以1.5倍扩容,不过这里取整了。 如果不想扩容发生,就用reserve提前先开好空间。
void test_vector2()
{
size_t sz;
vector<int> v;
v.reserve(100);
sz = v.capacity();
cout << "making v grow:\n";
for (int i = 0; i < 100; ++i)
{
v.push_back(i);
if (sz != v.capacity())
{
sz = v.capacity();
cout << "capacity changed: " << sz << '\n';
}
}
}
这样就不用扩容了:
一般来说resize和reserve都不会缩容:
size_t sz;
vector<int> v;
v.reserve(100);
cout << v.size() << endl;
cout << v.capacity() << endl;
v.reserve(10);
cout << v.size() << endl;
cout << v.capacity() << endl;
cout << "-----------------" << endl;
cout << v.size() << endl;
cout << v.capacity() << endl;
v.resize(10);
cout << v.size() << endl;
cout << v.capacity() << endl;
要想缩容就调用这个接口shrink_to_fit
vector<int> v;
v.reserve(100);
cout << v.size() << endl;
cout << v.capacity() << endl;
v.reserve(10);
cout << v.size() << endl;
cout << v.capacity() << endl;
cout << "-----------------" << endl;
cout << v.size() << endl;
cout << v.capacity() << endl;
v.resize(10);
cout << v.size() << endl;
cout << v.capacity() << endl;
cout << "-----------------" << endl;
v.shrink_to_fit();
cout << v.size() << endl;
cout << v.capacity() << endl;
这样就实现了缩容:
vector只支持单个数据的尾插。 直接来看看代码:
#include<iostream>
using namespace std;
#include<vector>
int main()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
for (size_t i = 0; i < v.size(); i++)
{
cout << v[i] << " ";
}
cout << endl;
vector<int>::iterator it = v.begin();
while (it != v.end())
{
cout << *it << " ";
++it;
}
cout << endl;
return 0;
}
来试试头插:
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
v.insert(v.begin(), 0);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
也可以插入一段迭代区间:
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
v.insert(v.begin(), 0);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
string s("abcd");
v.insert(v.begin(), s.begin(),s.end());
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
这里隐私类型转换,将abcd转换为对应的ascii值:
尾删
来看看代码:
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
for (size_t i = 0; i < v.size(); i++)
{
cout << v[i] << " ";
}
cout << endl;
v.pop_back();
for (size_t i = 0; i < v.size(); i++)
{
cout << v[i] << " ";
}
cout << endl;
v.pop_back();
for (size_t i = 0; i < v.size(); i++)
{
cout << v[i] << " ";
}
cout << endl;
在vector里面发现没有find,如果我们想要使用find来查找,那么就得用到算法库里面的就行。使用它得包含一个头文件:#include<algorithm>
举个例子:在3位置插入30
#include<iostream>
#include<algorithm>
using namespace std;
#include<vector>
int main()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
vector<int>::iterator pos=find(v.begin(), v.end(), 3);
if (pos != v.end())
{
v.insert(pos, 30);
}
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
}
举个例子删除3位置:
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
vector<int>::iterator pos = find(v.begin(), v.end(), 3);
if (pos != v.end())
{
v.erase(pos);
}
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
有问题请指出,大家一起进步!!!