The difference between cout/cerr/clog

cout/cerr/clog All are C++ Standard output stream provided , What's the difference between these three ？
cout: Standard output stream , Generally, the buffer is not refreshed until the buffer is full or the program ends
cerr: Standard output error , Output a statement will flush the buffer once
clog: Standard output log , Relatively speaking, the frequency of refreshing the buffer is not high

Let's start with a simple example

#include<iostream>

int main()
{
    
	std::cout << "output to cout";
	std::cerr << "output to cerr";
	std::clog << "output to clog";
}

If we run the program directly , Then these three lines will be output to the screen

however , If we redirect output , that cout and cerr/clog Will be output to different files （0 Represents standard input ,1 Indicates standard output ,2 Represents standard error output ）

that , Given the cerr, Why do we have to clog？

We all know that the program input and output will have buffers , The buffer is in memory , The file is on disk , The program accesses memory much faster than the disk . So in order to improve efficiency , The program will output to the buffer first , It will not be written to the disk file until the buffer is full or when the refresh buffer is displayed . But if the buffer is not full , Now the program crashes , Then the data in the buffer will be lost , relatively speaking cerr Error messages will be important , To ensure that the error information is written to the disk file , The program often flushes the buffer .clog Log information is relatively less important , Therefore, the buffer will not be refreshed often （ Be careful ： Frequent buffer flushing will slow down the running speed , Because of frequent access to disk content ）

std::flush： Refresh buffer
std::endl： Flush the buffer and wrap
Generally, the program will not refresh the buffer until the end of the program , But sometimes we don't want to refresh the buffer but want to add a newline , Then use escape characters \n

#include<iostream>

int main()
{
    
	std::cout << "output to cout\n";
	std::cerr << "output to cerr\n";
	std::clog << "output to clog\n";
}