1) STL literacy
1）C++标准库和标准模板库是不一样的
2）标准模板库是用泛型编程方式编写的函数或者类库;
3) SGI STL linux一般用，P.J.Plauger STL,visual2017 windows用
STL六大组件 :
容器，迭代器
STL 算法(说白了就是函数！)；
STL 分配器:（分配内存的，也叫内存分配器）allocator [ˈæləˌkeɪtə]
适配器和仿函数
convert 转换，converge 汇聚，收敛
容器分类：顺序容器，关联容器(associate [əˈsəʊsɪˌcontainer)，无序容器;注意：associate的第一个as是ad变体，表示靠近的意思
deque 双端队列:double end queue
foward_list是单向链表
2) In stl::array, when storing strings, memory relationship examples:
#include<iostream>
#include<array>
using namespace std;
int main()
{
array<string, 5> arr{
"1232222222222222222","456","aaaaaaa"};
cout << sizeof(string) << endl; //28个字节
for (int i = 0; i < arr.size(); ++i)
{
const char* p = arr[i].c_str();
cout << "---------------------begin-----------------" << endl;
cout << "数组元素值= " << p << endl;
printf("对象地址= %p\n", &arr[i]);
printf("指向字符串地址= %p\n", p);
cout << "---------------------end-----------------" << endl;
cout << endl;
}
const char* p1 = "1232222222222222222";
const char* p2 = "1232222222222222222";
printf("p1地址= %p\n", p1);
printf("p2地址= %p\n", p2);
return 0;
}
//Output result
28
------------------------begin-----------------
array element value = 1232222222222222222
object Address = 012FFA74
points to string address = 016BD988
--------------------------end-----------------
--------------------------begin-----------------
Array element value = 456
Object address = 012FFA90
pointing character String address = 012FFA94
--------------------------end-----------------
--------------------------begin-----------------
Array element value = aaaaaaa
object address = 012FFAAC
pointing character String address = 012FFAB0
--------------------------end-----------------
--------------------------begin-----------------
Array element value =
object address = 012FFAC8
points to string Address = 012FFACC
--------------------------end-----------------
--------------------------begin-----------------
Array element value =
object address = 012FFAE4
points to string Address = 012FFAE8
--------------------------end-----------------
p1 address = 0094DC74
p2 address = 0094DC74
//From the above results, it can be seen that: 1) the byte size of the string string is 28, 2) the string array addresses in the array differ by 28 bytes, but the string addresses pointed to are not next to each other.
//3 Define two string constants, but the string address they store actually only has one address! ! !
3) Vector construction copy learning
#include<array>
#include<vector>
#include<iostream>
using namespace std;
class A
{
public:
A(int a) :m_(a) {
cout << "A constructor" << endl; }
A(const A& obj):m_(obj.m_){
cout << "A copy constructor" << endl; }
~A(){
cout << "A deconstructor" << endl; }
private:
int m_;
};
int main()
{
vector<A> vec;
//vec.reserve(10); 根据实际情况，调用这个函数，设置存储空间大小，就可以减少不必要的拷贝和析构；
for (int i = 0; i < 5; i++)
{
cout << "---------------------begin-----------------" << endl;
vec.push_back(A(i));
cout << "---------------------end-----------------" << endl;
}
return 0;
}
---------------------begin-----------------
A constructor
A copy constructor
A deconstructor
---------------------end-----------------
---------------------begin-----------------
A constructor
A copy constructor
A copy constructor
A deconstructor
A deconstructor
---------------------end-----------------
---------------------begin-----------------
A constructor
A copy constructor
A copy constructor
A copy constructor
A deconstructor
A deconstructor
A deconstructor
---------------------end-----------------
---------------------begin-----------------
A constructor
A copy constructor
A copy constructor
A copy constructor
A copy constructor
A deconstructor
A deconstructor
A deconstructor
A deconstructor
---------------------end-----------------
---------------------begin-----------------
A constructor
A copy constructor
A copy constructor
A copy constructor
A copy constructor
A copy constructor
A deconstructor
A deconstructor
A deconstructor
A deconstructor
A deconstructor
---------------------end-----------------
A deconstructor
A deconstructor
A deconstructor
A deconstructor
A deconstructor
description:
//The main reason for the above problems is that vector storage is continuous. When storing data, the size of the storage space must be constantly adjusted, so copying and destruction will continue; //Solve the
above One way is to reserve a space at the beginning and call the reserve function, so as to reduce unnecessary copies and destruction;
4) Use cases of allocators
#include<iostream>
#include<list>
using namespace std;
int main()
{
std::list<int> list;
list.push_back(10);
list.push_back(20);
list.push_back(30);
list.push_back(40);
for (auto it = list.begin(); it != list.end(); it++)
{
int* ptr = &(*it);
printf("element address is: %p\r\n", ptr);
}
return 0;
}
//输出结果是（输出地址根本不联系！！！）：
element address is: 011DFEC0
element address is: 011E0240
element address is: 011E0278
element address is: 011E0010
结论：上述代码中，缺省的分配器根本没有用内存池技术，应该采用的是malloc这个技术！
//使用分配器的方法：
using namespace std;
//不建议直接使用
int main()
{
std::allocator<int> allo;
int* ptr = allo.allocate(3);
*ptr = 1; ptr++;
*ptr = 2; ptr++;
*ptr = 3;
allo.deallocate(ptr,3);
return 0;
}
5) Use of iterators
迭代器是一个对象(确切的说，类似于一个指针的对象);
迭代器和容器是紧密相关的。
迭代器是分类标准：迭代器的移动特性和数据访问操作；
输出迭代器，输入迭代器，前向迭代器，双向迭代器，随机访问迭代器
output_iterator_tag
iterator、const_iterator、reverse_interator、const_reverse_interator
有些模板类不提供迭代器，比如stack,deque,queue等；
typename修饰模板类型
typename iterator_traits<T>::iterator_category cagy; //"iterator_traits<T>::iterator_category"是一个类型，typename是说明类型的
#include<iostream>
#include<vector>
using namespace std;
template<typename T>
void printMsg(const T& tmp)
{
if (tmp.size() >= 2)
{
typename T::const_iterator iter(tmp.begin()); //错误提示：“const_iterator” : 类型 从属名称的使用必须以“typename”为前缀，所以必须添加为typename
int val = *iter;
cout << val << endl;
}
}
int main()
{
std::vector<int> v{
1,2,3,4 };
printMsg(v);
return 0;
}
6) Overview of STL algorithm
The algorithm is understood as a function, more precisely, it is a function template (global function/global function template). The
first two parameters of the algorithm are mostly an iterator interval!
The advantage of closing in front and opening in back: As long as the algorithm determines that the iterator is equal to the open interval in the back, it means that the iterator is over;
if iterator_begin==iterator_end, it means that it is an empty interval;
the algorithm is a global function used with the iterator. The algorithm has nothing to do with containers, only iterators.
for_each(begin,end,可调用对象)；
仿写for_each遍历算法代码如下：
void printMsg(int i)
{
cout << i << endl;
}
template<typename inputIterator,typename Fun>
void fun(inputIterator first, inputIterator end, Fun f)
{
for (; first != end; first++)
{
f(*first);
}
}
int main()
{
std::vector<int> vec{
1,2,3,4,5 };
fun(vec.begin(), vec.end(), printMsg);
return 0;
}
6.1) How to use sort:
sort中的仿函数调用对象
class A
{
public:
bool operator()(int i,int y)
{
if (i > y)return true;
else return false;
}
};
int main()
{
std::vector<int> vec{
1,20,13,54,51 };
A a;
sort(vec.begin(), vec.end(),a);
for (auto it = vec.begin(); it != vec.end(); it++)
{
cout << *it << endl;
}
return 0;
}
adjacent：[əˈdʒeɪsnt] 临近的；
饿滴 家
ad是强调的作用，jac是ject的变体 记忆方法 ad ja cent (我的家距离我近，回家可以吃饭）
7) Learning of function objects
函数对象也叫仿函数，是一个意思
在stl中，函数对象一般都合算法配合使用，实现一些特定功能，主要服务于算法！！！
标准模板库也给我们提供了一些函数对象，头文件包含<functional>，大概有十八个样子；
plus<int>(); //对这句话的解释：plus是类模板,加上"<int>"才可以成为真正的类plus<int>,再加上"()",生成一个临时对象，就是个可调用对象；
使用方法如下：
std::vector<int> vec{
1,20,13,54,51 };
sort(vec.begin(), vec.end(), greater<int>());
for (auto it = vec.begin(); it != vec.end(); it++)
{
cout << *it << endl;
}