3-container
References
声明引用时，必须有引用的变量，而且不能用右值初始化引用，右值就是 i*3+1 之类的，
不能用其它引用进行初始化，指针不能指向引用，指针可被引用，没有引用数组这种东西
void func(int &);
func (i * 3); // Warning or error!
char c = 'A';
char &r = c;
r = 'B';
cout << "c: " << c << endl;
cout << "b: " << b << endl;
//输出都是 B
int y = 1;
void f (int& x);
f(y)
//别名x在函数被调用时初始化
const int& z = x; 这里的 const 只对限制引用， 但 x 依然可写
然后引用作为参数在函数里可以直接影响本值
void f(int &x){
x++;
}
int main(){
int a = 51;
cout << "a=" << a << endl;
f(a);
cout << "a=" << a << endl;
}
//51 52
- References
- can't be null
- are dependent on an existing variable, they are an alias for an variable
- can't change to a new "address" location
- Pointers
- can be set to null
- pointer is independent of existing objects
- can change to point to a different address
Container
Collection objects are objects that can store other objects.
容器在 STL 中，STL = Standard Template Library
Library includes
- A
pairclass (pairs of anything, int/int, int/char, etc) - containers
vector(expandable array)deque(expandable array, expands at both ends)list(double-linked)setsandmaps
- Basic Algorithms (
sort,search, etc)- All identifiers in library are in std namespace
Vector
每个容器对应一个头文件，需要 include. 如 #include<vector>.
#include <iostream>
#include <vector>
using namespace std;
int main( ) {
vector<int> x; // Declare a vector of ints (no worry about size)
for (int a=0; a<1000; a++)
x.push_back(a); // Add elements
// Have a pre-defined iterator for vector class, can use it to print out the items in vector
vector<int>::iterator p;
for (p=x.begin(); p<x.end(); p++)
cout << *p << " ";
return 0;
}
vector<int>::iterator 是一个类型，p 发挥了类似链表里指针的作用
但 p 并不是指针，利用了 C++ 的运算符重载
//Constructor
vector<Elem>c;
vector<Elem>c1(c2);
//Methods
V.size(); // num items
V.empty(); // empty?
==, !=, <, >, <=, >=
V.swap(v2); // swap
//Iterators
I.begin() // first position
I.end() // last position
//access
V.at(index)
V[index]
V.front() // first item
V.back() // last item
//Add/Remove/Find
V.push_back(e)
V.pop_back()
V.insert(pos, e)
V.erase(pos)
V.clear()
V.find(first, last, item)
vector 的空间是保证连续的，物品是保证按push顺序存放的
被 push 的元素是被复制到 vector 里面，类型会自动转化为 vector 的类型
List
x.push_back(item)
x.push_front(item)
x.pop_back()
x.pop_front()
x.remove(item)
#include <iostream>
#include <list>
#include <string>
using namespace std;
int main()
{
list<string>s;
s.push_back("hello");
s.push_back("world");
s.push_front("tide");
s.push_front("crimson");
s.push_front("alabama");
list<string>iterator:: p;
for (p=s.begin(); p!=s.end(); p++)
cout << *p << " ";
cout << endl;
}
list<int> L;
for(int i=1; i<=5; ++i)
L.push_back(i);
//delete second item.
L.erase( ++L.begin() );
copy( L.begin(), L.end(),ostream_iterator<int>(cout,",")); //Prints: 1,3,4,5,
list 空间是动态分配的（见缝插针），后申请的空间不能保证在先申请的空间后面，所以这里用 p!=s.end()
Maps
存储的是一堆二元映射，每个映射有一个 key 和 一个 value，表示 key->value
能想象到会有 method 是通过输入 key 获取 value
其实就是有类型拓展的数组嘛，index 和值可以改成任意类型了
#include <map>
map<long,int> root;
root[4] = 2;
root[1000000] = 1000;
long l;
cin >> l;
if (root.count(l))
cout<<root[l]
else cout<<“Not perfect square”;
-
Use
empty()onlist<>
Iterators
迭代子，专门用于遍历容器的一种变量类型，以 list 为例：
list<int>::iterator li; //Declaring
list<int>L;li = L.begin(); //Front of container
li = L.end(); //Past the end
li=L.begin();
++li; // Second thing - Can increment
*li = 10; //Can be dereferenced
for(type variable_name : array/vector_name) {
...
}
//for-each loop，获得的值都是只读的
int arr[]={1,2,3,4,5}; //array initialization
cout<<"The elements are: ";
for(int i : arr) // auto
{
cout<<i<<" ";
}
for-each loop 不需要预先初始化迭代器，缺点是不能获得下标，不能逆序遍历，不能跳过某个单元，不能修改容器的值
Pitfalls
-
Accessing an invalid
Solutions
- use
push_back() - Preallocate with constructor.
- Reallocate with
reserve() - Check
capacity()
- use
-
Inadvertently inserting into
map<>Solutions: Use
count()to check for a key without creating a new entry：if ( foo.count("bob") )
count()方法返回值是一个整数，1表示有这个元素，0表示没有这个元素
-
Use invalid iterator