Ctrl+Z behaviour in terminal

Question

string s;
while(getline(cin,s)){
    cout << "---" << endl
    for(auto c: s) cout << int(c) << endl;   
}
cout << "Exiting";

If my input is Ctrl + Z , then I press enter once, and my program exits immediately.

^Z
Exiting

If I enter a character before pressing Ctrl + Z , then I have to press enter twice, and my program does not exit.

s^Z

---
115
26

I had always interpreted Ctrl + Z as the EOF character. getline would continue until it reaches this character, at which point getline tests false and my program would exit. I'm curious why my program interprets Ctrl + Z as the substitute character 26, depending on whether there is a preceding character or not, and why it was necessary for me to press Enter twice in the second example?

Answer 1

26 is code of ^Z on your platform , and ^Z is a EOF marker for terminal, that's true. Characters with codes less than 32 are control characters for ASCII -compatible platform, I hope you know that. 26 isn't a substitute character, it's actual control code, ^Z or some "bug" character are substitutes. getline reads input until EOL (end-of-line, designated as CR by ASCII) or EOF (end of file, end of stream, designated as SUB) is encountered in stream, so ^Z is read with the second call of getline . That behavior is absolutely correct.

It is defined by platform (or, more precisely, by terminal type) if characters are sent to input buffer immediately or after some flush command occurred. Usual cause of buffer flush is EOL character, that's your ENTER (CR - Carriage return). Tat's why program receives EOF after Enter in your case. Note that some platform use LF (line feed) as EOL, and some - a pair of LF+CR. C literal '\\n' is to be correctly translated into particular EOL marker.

Note, that you can use different delimiter:

template< class CharT, class Traits, class Allocator > 
std::basic_istream<CharT,Traits>& getline( 
         std::basic_istream<CharT,Traits>& input,
         std::basic_string<CharT,Traits,Allocator>& str,
         CharT delim );

ASCII table with substitute Control+ :