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int、short、long、long long These four types belong to the symbol type , They all have corresponding unsigned variants that cannot store negative values , The advantage is to increase the maximum value that a variable can store （ Is to give the space of a negative number to a positive number ） Of course , Only if the value is not negative , Only unsigned types should be used . Such as population 、 The number of trees, etc . Create an unsigned version of a basic type , Just use keywords unsigned that will do .

for example ：

unsigned short change;
unsigned int a;
unsigned c;				// It also refers to the unsigned type corresponding to the integer 
unsigned long f;
unsigned long long v;

2、 The understanding of array names

Array names are treated as pointers .c++ Interpret the array name as the address of its first element .

3、 The basics of function pointers

（1） Get the address of the function

Just use the function name （ It's not followed by parameters ） You can get the address of the function , for instance L If think（） Is a function , that think Is the address of the function , Just pass the function as an argument , Function name must be passed . At this point, it is necessary to distinguish whether the address of the function or the return value of the function is passed .

process(think);// Pass on think The address to progress()
thought(think());// Pass on think() The return value of is given to thought()

（2) Declared function pointer

When declaring a pointer to a data type , You must specify the type that the pointer points to . Also when declaring a pointer to a function , You must also specify the type of function the pointer points to .

4、 Inline function

About the format ：

Add the keyword before the function declaration inline

Add keywords to the function definition inline

5、 quote

A reference variable can be understood as an alias for a defined variable . The main function of a reference variable is to use it as a formal parameter of a function . By using reference variables as parameters , The function will use the raw data , Not a copy , In plain terms, it means changing any of the values , Another variable will follow .（ In this way , Except pointer , References also provide a very convenient way for functions to deal with large structures ）

Here's an example ：

＃include<iostream>
using namespace std;
int main()
{	int a=101;
	int &b=a;
	return 0;}

// Please note that , Of the following statement ＆ Operator is not an address operator , Among them ＆a Express a The address of the referenced variable 
int &a=b;

Simple examples help understand ：

#include<iostream>
using namespace std;
int main()
{
	int a;
	int &bb=a;
	a=100;
	cout<<&bb;		   	// Output bb The corresponding address （ It should be with a The address of is the same ）
	cout<<endl<<bb;	    // Output bb（ That is to say a Value , because bb Refer to the a）
	
	
	return 0;}

The difference between reference and pointer

There are some subtle differences between references and pointers , For example, you must initialize a reference before declaring it , But not like a pointer , Declare before assign .

6、 File operations

Reading documents

fstream It refers to the file stream containing write and read , As defined here a Is a file stream object , The following prescribed reading and writing methods are out That is, writing to a file . hinder is_open function , It is used to judge whether the file is opened .

a<<"......" It refers to the contents written to the file . Every time I run , These are the contents of the generated file , the reason being that out Write mode of , Each run will first delete the information in the previous file , If you want to make a tail adding operation , Then it should be changed to app To read and write files . In this way, the records will be preserved , Make ATM It should be used to simulate the system app How to operate .

After the operation is completed , Don't forget to close the link corresponding to the file .

Be careful ： When there is no generated file , The system will automatically generate a file with this name . If so in( Read file operation ), So it's a mistake , If so out, Will be generated automatically .

#include<iostream>
#include<fstream>
using namespace std;
int main()
{
fstream a;
a.open("test.txt",ios::out); 
if(!a.is_open()) 
	cout<<"can not open the file";
a<<" The exam is coming soon, and I won't do anything "<<endl<<" Hold on to the last minute ！"<<endl;
a.close();
return 0;
 }

Writing documents

#include<iostream>
#include<fstream>
using namespace std;
int main()
{
fstream s;
string message;
s.open(" Read and write operation of the file .txt",ios::in);
if(s.is_open())
	{
	cout<<" The file was successfully opened or created "<<endl;
	}
else
	cout<<" File opening failure ";
s>>message;
s.close();
cout<<message;
return 0;}

Read the information in the file read / write operation , Then output the obtained information , Follow up work .

make_pair and pair The difference between

make_pair():

There is no need to write the type , You can generate a pair object
example ：
std::make_pair(42, '@');
It doesn't have to be written as ：
std::pair<int, char>(42, '@')

find Function combination map（multimap） Lookup

algorithm Of the header file find（）.
Usage method ：find（begin,end,value）, It's usually used Containers .end（） To determine whether the search is successful .
Parameters 1 Is the starting address of the container or array （ Containers .begin（） Or array name ）, It can also be any address , It is not illegal ;

Parameters 2 Is the address where the search ends （ Containers .end() Or array name + length ）,value Is the character or string you want to find

A successful lookup will return the iterator （ Containers ） Or pointer （ Array ）, Otherwise return to end（）

find The return is an iterator

If you can't find , It will return end（）

void operation::find_idnum(string idnum1)
{
     m2=idnumc.find(idnum1);        // map<string,int>idnumc;
     if(m2!=idnumc.end())
         {
             cout<<" find "<<endl<<person[m2->second];    //vector<message>person;
         }
}

use equal_range Search for multimap The element interval of the qualified content of .

Use multimap、map Is automatically sorted , Will sort the information , So use lower_bound and upper_bound The found range can be used efficiently .

How container elements are inserted

have access to for Loop or while Loop through the insert operation , But then write the course design ATM operation period , Discover the use of while There will be an error while cycling , Or use for Revolving insurance （ After all, use while You need to write a lot of statements when looping , There may be some differences .）

Constructors 、 Destructors and file operations

Constructors 、 Destructors tend to be less attractive , But when we combine it with file manipulation , Should be in their function body if read file and write file operation .

Shallow replication and deep replication

Shallow copy concept

● When initializing one object with another , Only data members are copied , Without copying resources , The replication method that makes two objects point to the same resource at the same time is called shallow replication .

namely ： For data members of complex types Only the storage address is copied and No copy of stored content

● The default copy constructor does simple data copying , Shallow copy

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