output read string between getchar() calls

[LukeProducts]

Hello mates,

i dont understand what my code is doning and why.

#include <iostream>

int main()
{
    std::string msg;
    int c;

    while ((c = getchar()) != '\n')
    {
        msg.push_back(c);
        std::cout << "\nentered so far: " << msg << "\n";
    }
}

i dont understand why the output of f.ex. "Hello" is:

Hello
entered so far: H
entered so far: He
entered so far: Hel
entered so far: Hell
entered so far: Hello

i expect this behaviour:

H
entered so far: H
e
entered so far: He
l
entered so far: Hel
l
entered so far: Hell
o
entered so far: Hello

Why the hell is the actual variable msg not pushed back after each char entry but in the end?
Does anyone know how to achieve this?
Thank you very much.

sincerely,
Luke

[Peter87]

Input through command line is line buffered. That means the input you type will not be received by the program until you press Enter.

[LukeProducts]

thank you, this sounds plausible. is there any way to achieve my behaviour?

[Peter87]

Not using only standard C++. You can do it with the help of curses libraries (e.g. pdcurses on Windows and ncurses elsewhere). System dependent APIs, such as the "WinAPI" on Windows, can also do it (this is probably how the curses libraries are implemented).

[LukeProducts]

Thank you. ill have a look at that.
i also heared about getch() but i dont understand the documentation. if i replace getchar() with getch() from conio.h, i dont get any key printed to console but do get feedback from std::cout...
if i could just see the keystrokes..

[Peter87]

It was a very long time since I used conio.h and I don't remember what you could do with it exactly.

The curses libraries also have their own version of getch(). By calling other functions you can configure how you want it to behave. Whether you want the the letters to be printed, whether you want to wait for input or return immediately, whether you want to read "key codes" rather than characters, etc.

I don't remember all the details but I think the curses libraries have more features compared to conio.h. Other things you can do is change the color and position of the text.

[Peter87]

Among the curses libraries I only really have experience with ncurses, but it looks mostly the same as pdcurses so I suspect it should be possible to write code that works with both.

[LukeProducts]

Thank you very much. ive just figured out how getch works

c = getch()
putchar(c)
...

does the thing with even no additional include lib.

[seeplus]

if i replace getchar() with getch() from conio.h, i dont get any key printed to console

Correct. getch() doesn't echo the typed char. If you want the typed char to be echoed then use getche().

Note that for Windows VS, these should be _getch() and _getche().

The other functionality provided with conio.h that may be of interest is kbhit() (or _kbhit() ). This returns non-zero if a character has been entered and 0 if not- without obtaining the char.