getchar() giving a hardtime

xunilpassion · 12-04-2003, 10:24 AM

Hi all,

The getchar() function provide a hardtime for me. I am using GCC 3.2.3.

#include <stdio.h>

int main() {
int c;
c=getchar();
putchar(c);
}

I expects that as soon as i enter a character the execution should proceed with out blocking. However I am forced to hit <enter> after i input a character. Am I doing anything wrong. I don't remember, i had this problem in previous versions of gcc (I can't assertively say it though, because it is long time since i have written something in C. I rather have a bleak memory on how it was before)

The background is if you run the following snippet

#include <stdio.h>
int main() {
int c;
while((c = getchar()) != EOF)
putchar(c);
}

The while loop goes in infinite loops. There is no way to enter an EOF character (which I persume is ^Z). If i press ^Z, the execution stopes. If I hit ^C the execution breaks.

What is going on ?

~xunil

jinksys · 12-04-2003, 11:22 AM

I think a previous post of mine can help...
http://www.linuxquestions.org/questi...hlight=getchar

jim mcnamara · 12-04-2003, 12:22 PM

Also check out conio.h or curses.h
If either of these include files are present your compiler will support
the getch() and the getche() function -- just what you want.

xunilpassion · 12-04-2003, 01:44 PM

Well, I got it worked. getch helped me. However, i was also having problems in getting out of the while loop. In each terminals i think the EOF character is different. CTRL-D is one working for me. My xterm is a gnome terminal. I remember using ctrl-z in dos for EOF.

Do anyone have more info on this

~xunil

jinksys · 12-04-2003, 02:52 PM

Youre problem is not with GCC but with how the shell behaves.
If you want to be able to enter a character without having to press
enter afterwards, you are going to have to do some programming of
your own. Also, conio.h does not exist under linux, it is a borland made header. A few people have written or tried to write a conio-like library, but ncurses is still much much better.

If you want, here is my crafted Getchar function that does all the work for you:

Code:

char Getchar(void) {
char x;
//Set terminal to raw mode
system("stty raw");

//Wait for single character
x=getchar();

//Reset terminal to normal "cooked" mode
system("stty cooked");

//And we're out of here
return x;
}

here is a small example that uses it.

Code:

int main()
{
char x;
x=Getchar();
printf("%c",x);
return 0;
}

If you do use the function, dont forget to declare it first.

dorian33 · 12-04-2003, 04:19 PM

another C code that implements DOS-like getch() function:

Code:

#include <termios.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
/*------------------------------------------------*/
unsigned char getch(void) {
 unsigned char c;
 int i;
 struct termios org_opts, new_opts;
 int res;
//-----  store old settings -----------
    res=tcgetattr(STDIN_FILENO, &org_opts);
    assert(res==0);
//---- set new terminal parms --------
    memcpy(&new_opts, &org_opts, sizeof(new_opts));
    new_opts.c_lflag &= ~(ICANON | ECHO | ECHOE | ECHOK | ECHONL | ECHOPRT | ECHOKE | ICRNL);
    tcsetattr(STDIN_FILENO, TCSANOW, &new_opts);
    c=getchar();
//------  restore old settings ---------
    tcsetattr(STDIN_FILENO, TCSANOW, &org_opts);
    assert(res==0);
    return(c);
}

More coding but without extra processes generated by 'system' call.

Tarts · 12-04-2003, 06:01 PM

Heres a little something I made:

Code:

#include <termios.h>
#include <stdio.h>

struct termios save_att;
set_terminal(void)
{
        struct termios set_att;
        set_att.c_iflag &= ~(INLCR);
        tcgetattr(0, &save_att);
        tcsetattr(0, TCSANOW, &set_att);
}

reset_terminal(void)
{
        tcsetattr(0, TCSANOW, &save_att);
}

int main()
{
        int c;
        set_terminal();
        c = getchar();
        reset_terminal();
        putchar(c);
        return 0;
}

Tarts
{edit}

Opps, it looks like dorian33 did something simliar, or better.

With the help of the post above:

Code:

#include <termios.h>
#include <unistd.h>
#include <stdio.h>
#include <strings.h>

char charget() //I think this thread has the monopoly on 'getchar()' derivatives. 
{
        char c;
        struct termios save_att, set_att;  //learned from the post above when accessing multiable variables in a structure
        tcgetattr(0, &save_att);
        set_att.c_lflag &= ~(ICANON|ECHO|ICRNL);
        tcsetattr(0, TCSANOW, &set_att);
        c = getchar();
        tcsetattr(0, TCSANOW, &save_att);
        return c;
}

int main()
{
        int i;
        i = charget();
        putchar(i);
        return 0;
}

Tarts