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Linux Instruction how to check the memory occupation , How to check the occupied port

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lsof

An array a[20][10] The first address of 100, ask a[11][5] What is the address of

As indicated in the question , Its representatives a[0][0] The address for 100;
So for 100+11410+5*4=560;

Memory storage and insertion of arrays and linked lists

Array storage is continuous , Convenient query , But it is inconvenient to insert ;
Linked list storage is not continuous , It's not convenient to inquire , But easy to insert ;

unordered_map and map The underlying implementation of , And how to choose the usage scenario

unorde_map Implementation based on hash table ;
map Based on black mangrove ;

#include when “” and <> The difference between

#include<>： The compiler looks for the header file directly from the system class library directory ：
#include""： Find the project header from the default directory , Current project directory , It is the project engineering document （.vcxproj） directory . If the search fails under the current directory of the project , Then find the header file from the header file reference directory of the project configuration , The reference directory of the so-called project configuration , It is the header file reference directory we set in the project . If the search still fails in the header file reference directory of the project configuration , Then look for the header file from the system class library directory

vector When adding elements , Memory changes and push_back Pointer is used 、 Reference or copy

size()++;
capacity unchanged ;
If it exceeds, allocate 1.5 perhaps 2 Times the size of memory ;
Push_back Copy is used , Class also uses copy

TCP/UDP The difference between

1. Whether it's connection oriented
2. reliable
3. Whether it supports one to many
4. Consumed resource size ,
5. Head length

TCP How to ensure its reliability

• The checksum
• flow control （ Face two ports ）、 Congestion control
• Serial number and confirmation of receipt ;
• Three handshakes, four waves ;
• Over time retransmission

Interprocess communication method

• The Conduit
• Shared memory
• Message queue
• The signal
• Semaphore
• socket Socket

socket Compared with other advantages

Processes on different hosts can communicate ;

1. The transmission data is byte level , Transfer data can be customized , Small amount of data （ For mobile applications ： Low cost ）

2. Short data transmission time , High performance

3. It is suitable for real-time information interaction between client and server

4. Can encrypt , Strong data security

Write Bytes next time , That's all for this time 23333