Get a string without displaying it on the console

Question

I want to get a string (with space) from user but I don't want it to display on the console. Is there any way in the C language that makes it possible?

Not in standard C. For all you know, there might not even be a console. — chris, Jul 18 '14 at 17:09
Maybe have a look at (n)curses, or give the platforms, where your program should run. — mafso, Jul 18 '14 at 17:28
The closest you'll get to anything standard is `getpass`. See this question on possible alternatives: http://stackoverflow.com/questions/1196418/getting-a-password-in-c-without-using-getpass-3 — Ross Ridge, Jul 18 '14 at 17:31
[graphics] seems a rather inappropriate tag here. Found nothing related to console input? — Jongware, Jul 18 '14 at 17:50

score 4 · Answer 1 · answered Jul 18 '14 at 17:35

4

I guess you want to disable echoing characters typed by user. You can do that by setting the terminal attributes using functions from <termios.h> like this:

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

#define MAX_LINE_SIZE 512

int main (int argc, char *argv[])
{
   /* get terminal attributes */
   struct termios termios;
   tcgetattr(STDIN_FILENO, &termios);

   /* disable echo */
   termios.c_lflag &= ~ECHO;
   tcsetattr(STDIN_FILENO, TCSAFLUSH, &termios);

   /* read a line */
   char line[MAX_LINE_SIZE] = { 0 };
   fgets(line, sizeof(line), stdin);

   /* enable echo */
   termios.c_lflag &= ~ECHO;
   tcsetattr(STDIN_FILENO, TCSAFLUSH, &termios);


   /* print the line */
   printf("line: %s", line);

   return 0;
}

The example above reads one line (without echoing the characters back) and then it just prints the line back to the terminal.

answered Jul 18 '14 at 17:35

Dmitry

1,995
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Is it using header files of Visual c? – snj Jul 18 '14 at 17:49
Sorry, but it is for a Unix environment. The C language is rare for Windows at these days, so I thought you have a Linux environment or something similar. Windows doesn't have (at least), perhaps you may find an equivalent here: http://stackoverflow.com/questions/933745/what-is-the-windows-equivalent-to-the-capabilities-defined-in-sys-select-h-and-t – Dmitry Jul 18 '14 at 18:08
For me, the terminal remains unwilling to echo after -reenabling echo. – Barny Aug 31 '22 at 03:41
it works properly if the original termios is stored and restored. This requires two termios structs. Your version fails to display my text afterward. – Barny Aug 31 '22 at 03:57

score 3 · Accepted Answer · edited May 23 '17 at 12:13

You can implement your own version of getch like so, and mask it. The following example spits out the input just for logging/testing purposes. You can disable that by removing the printf calls.

Good luck!

Code Listing

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

int getch();

int main(int argc, char **argv) {
   int ch;
   printf("Press x to exit.\n\n");
   for (;;) {
      ch = getch();
      printf("ch = %c (%d)\n", ch, ch);
      if(ch == 'x')
         break;
   }
   return 0;
}

int getch() {
   struct termios oldtc;
   struct termios newtc;
   int ch;
   tcgetattr(STDIN_FILENO, &oldtc);
   newtc = oldtc;
   newtc.c_lflag &= ~(ICANON | ECHO);
   tcsetattr(STDIN_FILENO, TCSANOW, &newtc);
   ch=getchar();
   tcsetattr(STDIN_FILENO, TCSANOW, &oldtc);
   return ch;
}

Sample Run

gcc test.c  && ./a.out


Press x to exit.

ch = a (97)
ch = b (98)
ch = c (99)
ch = 1 (49)
ch = 2 (50)
ch = 3 (51)
ch =
 (10)
ch =
 (10)
ch = x (120)

References

Hide password input on terminal, Accessed 2014-07-18, <https://stackoverflow.com/questions/6856635/hide-password-input-on-terminal>

Get a string without displaying it on the console

2 Answers2