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Cs61abc sharing session (VI) detailed explanation of program input and output - standard input and output, file, device, EOF, command line parameters

2022-07-29 07:37:00 【Sanfeng grocery store】

List of articles

Sharing session link

2022 year 7 month 23 Long term link to the daily sharing meeting ：https://meeting.tencent.com/dm/Qet4sVXmOccd

Share time ：9 spot 20 To 9 spot 50
The video is recorded at the bottom

standard output /dev/stdout

It's the keyboard
Display... On the terminal .

The standard error /dev/stderr

error message
It is also displayed on the terminal .
Although it shows in the same place , But you can and stdin distinguish . By redirecting symbols >

Interactive standard input /dev/stdin

Line breaks and spaces distinguish each input .

3
a 1 bccc

python For example ：

try :
	while True:
	    line = input()
	    # process line
except EOFError:
     pass

How to deal with it EOF Well ？

EOF Ending standard input /dev/stdin

End Of File Abbreviation , This character usually exists at the end of the file to indicate the end of the file .

EOF Express

In the end ：CTRL + D
C In language ：-1, The header file has a definition stdio.h
python: An empty string
stay Linux In the system ,EOF Not a character at all , But when the system reads the end of the file , A signal value returned （ That is to say -1）. As for how the system knows the end of the file , According to the data, it is by comparing the length of the file .

EOF Handle

Without user input , Then use standard output .
Use input The way ：

try :
	while True:
	    line = input()
	    # process line
except EOFError:
     pass

Use stdin The way , encounter EOF It's empty ：

while True:
    line = sys.stdin.readline()
    if line = '':
        break
    else:
        # Do what
        pass

C++ The way , encounter EOF, The return value is 0：

while (cin >> a) {
// process
}

File input and output

Input direct full read .
Output doesn't matter EOF.
But there is a EOF Of .

Linux Device output and redirection

/dev/null
/dev/zero
1 The standard input
2 standard output
The default is to process standard input ：./p.py > a.txt
If you want to change it , Explain the changes clearly . yes 1 The file of , still 1 This stdin
1 >&2
1 > /dev/null 2 >/dev/null

stay shell Application in

if cat a ;then
:
fi

if cat a 1 > /dev/null 2 >/dev/null;then
:
fi

Input of command line parameters

debug

All inputs and outputs are ok debug, But I don't know pycharm Words , There may be a hole .
pycharmdebug when , Input the standard, input the unresponsive processing method
stay pycharm in debug Note that deselect .