[interview arrangement] 0211 game engine server

Self introduction.

Project introduction

C++

• Principle and process of realizing polymorphism

  • 1） When the compiler finds a virtual function in the base class , A virtual table is automatically generated for each class containing virtual functions , The table is a one-dimensional array , The virtual table holds the entry address of the virtual function

  • 2） The compiler holds a virtual table pointer in the first four bytes of each object , namely vptr, Points to the virtual table of the class to which the object belongs . At tectonic time , Initialize the virtual pointer according to the type of the object vptr, So that vptr Point to the correct virtual table , So when you call a virtual function , You can find the right function

  • 3） The so-called right time , When a derived class defines an object , The program will automatically call the constructor , Create a virtual table in the constructor and initialize the virtual table . When constructing subclass objects , The constructor of the parent class will be called first , here , The compiler only “ I saw it ” Parent class , And initialize the virtual table pointer for the parent object , Let it point to the virtual table of the parent class ; When calling the constructor of a subclass , Initialize virtual table pointer for subclass object , Let it point to the virtual table of subclasses

  • 4） When the derived class does not override the virtual function of the base class , The virtual table pointer of the derived class points to the virtual table of the base class ; When a derived class rewrites a virtual function of a base class , The virtual table pointer of a derived class points to its own virtual table ; When a derived class has its own virtual function , Add the virtual function address to your own virtual table

  • So the base class pointer to the derived class at run time , Can be derived according to the virtual function rewriting dynamic call , So as to realize polymorphism .

• Can a constructor be a virtual function ？ Why? ？

  • （1） When creating an object, you need to determine the type of object , Virtual functions are dynamically typed at run time . When constructing an object , Because the object has not been created successfully , The compiler cannot know the actual type of the object

  • （2） Virtual function table pointer is required for calling virtual function vptr, The pointer is stored in the memory space of the object , If the constructor is declared a virtual function , So since the object has not been created , There is no memory space yet , There is no virtual function table vtable The address is used to call the dummy function

  • （3） The function of a virtual function is to become the member function of the subclass when it is called through the pointer or reference of the parent class . The constructor is called automatically when the object is created , It's impossible to call... Through a parent class or reference , Therefore, it is stipulated that the constructor cannot be a virtual function

• C++ Memory space

  • Stack
    • Store local variables 、 Function parameter
    • High efficiency but limited capacity
  • Pile up
    • Dynamic application for storage , Namely new Allocated memory
  • Free storage area
    • Between heap 、 Between stacks
  • overall situation / Static storage area
    • Store global variables and static variables
  • Constant storage area
    • Placement does not allow modification of constant data
  • Code section
    • Binary code for storing execution code

• new and malloc difference

  • new Failure to allocate memory is thrown bad_alloc abnormal ,malloc Go straight back to null
  • new Memory allocation is dynamically computed , Allocate in free storage ; and malloc You need to specify the size , Allocate memory on the heap
  • new/delete It's the operator , Can overload ;malloc/free yes C Standard library functions , Overloading is not allowed
  • new/delete Encapsulates the malloc/free, Except for distribution / Free out of memory , It also calls the constructor / Destructor
  • The former returns the pointer type at the time of definition , The latter returns void Type a pointer

• Commonly used STL Introduce the container

• map The structure of the underlying implementation

  • Red and black trees ,unordered_map At the bottom is the hash table

• Characteristics of the red black tree

  • First, satisfy the binary sort tree
  • All nodes are either black or red
  • The root node must be black
  • The children of the red node must be black , But the child nodes of the black node can be black
  • From roots to NULL The number of black nodes on any path of leaf nodes is the same

• Self balancing strategy of red black tree ？

  • （1） Color change ： The nodes of the red black tree change from red to black or from black to red

  • （2） left-handed ： With A node as a fulcrum （ Rotating fulcrum ）, Its right child node becomes the parent of the rotation node , The left child of the right child node becomes the right child of the rotating node , The left child node remains unchanged .

  • （3） Right hand ： With A node as a fulcrum （ Rotating fulcrum ）, The left child node becomes the parent node of the rotation node , The right child of the left child node becomes the left child of the rotating node , The right child node remains unchanged .

• vector Capacity expansion

  • Win+VS 1.5 times Linux+GCC 2 times

• C++11 New characteristics

• Introduction to smart pointer

• How to write a template class

• How to calculate the number of bytes of memory aligned structure in memory

computer network

• UDP and TCP difference

  • 1、TCP Connection oriented （ If you want to make a call, dial to establish a connection ）;UDP It's disconnected , That is, you don't need to establish a connection before sending data

  • 2、TCP Provide reliable service . in other words , adopt TCP Connect the transmitted data , No mistakes , No loss , No repetition , And arrive in order ;UDP Do your best to deliver , That is, there is no guarantee of reliable delivery

  • 3、TCP Byte stream oriented , It's actually TCP Think of data as a stream of unstructured bytes ;UDP It's message oriented

    UDP no congestion control , Therefore, the network congestion will not reduce the transmission rate of the source host （ Useful for real-time applications , Such as IP Telephone , Real time video conference, etc ）

  • 4、 Every one of them TCP Connections can only be point-to-point ;UDP Support one-to-one , One to many , Many to one and many to many interactive communication

  • 5、TCP First cost 20 byte ;UDP The cost of the first part is small , Only 8 Bytes

  • 6、TCP The logical communication channel of is a full duplex reliable channel ,UDP It's an unreliable channel

  • 7、UDP It's message oriented , The sender's UDP For the messages handed in by the application layer , Do not merge , Do not split , Just add a header on it and give it to the network layer below , On the application layer to UDP How many messages , It sends everything , Send one at a time . And docking with the recipient , Directly remove the head after receiving , Give it to the application layer above to complete the task . therefore , It requires the application layer to control the size of the message

    TCP Is oriented to a byte stream , It regards the data handed over by the upper application layer as a unstructured byte stream and sends , It can be imagined in the form of running water , The sender TCP Will put the data into “ Reservoir ”（ Buffer zone ）, Send when you can send , If you can't send it, just wait TCP The size of each message segment will be determined according to the current network congestion state .

• Four kinds of network programming IO Model

  • （1） Synchronous blocking IO（Blocking IO）： Traditional IO Model .

  • （2） Synchronous nonblocking IO（Non-blocking IO）： Created by default socket It's all blocked , Non blocking IO requirement socket Set to NONBLOCK. Pay attention to what's said here NIO Is not Java Of NIO（New IO） library .

  • （3）IO Multiplexing （IO Multiplexing）： Classic Reactor Design patterns , Sometimes called asynchronous blocking IO,Java Medium Selector and Linux Medium epoll It's all this model .

  • （4） asynchronous IO（Asynchronous IO）： Classic Proactor Design patterns , Also known as asynchronous non blocking IO.

• epoll ,poll and select

  • select At the bottom is a fd_set Data structure of , It's essentially a long An array of types , Each element in the array corresponds to a file descriptor , Check whether any event occurs by polling all file descriptors .

    advantage ：
    1、 Good portability ;
    2、 When the number of connections is small and the connections are very active , Good efficiency, too .

    shortcoming ：
    1、 The maximum number of file descriptors that can be monitored is 1024（ Because the kernel is written ）.
    2、 Polling traversal is used to check whether there are events , When there are many file descriptors, it is expensive .

    • poll and select almost , It's just poll There is no maximum number of file descriptions
    • epoll Is a more efficient IO The way of multiplexing , The number of file descriptors it can monitor has exceeded 1024 The limitation of （ One hundred thousand ）, At the same time, there is no need to check whether there is an event on the file descriptor through polling and traversal , because epoll_wait What is returned is the file descriptor where the event occurred . It is essentially event driven .

operating system

• The difference between multiprocessing and multithreading

  • There are multiple threads in the same process , Threads share the memory space of the process
  • Each process is the basic unit of resource allocation . The process structure consists of the following parts ： Code segment 、 stack segment 、 Data segment . Code snippets are static binary code , Multiple programs can be shared . In fact, after the parent process creates the child process , Father 、 In addition to pid Outside , Almost all parts are almost the same .

• pthred and std::thread difference

  • std::thread yes c++ Thread library in standard library , Its significance is that it can cross platform without changing the code

• Thread private data

  • Private data
    • Stack
    • state
    • register
    • Program counter
  • Shared data
    • Global variables
    • Data on heap
    • The static variable of the function
    • Program code
    • Open file

• gdb debugging

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