how to pass values into getchar in gdb

**bos1234** · 08-01-2020

I'm working through poker.c from King's C programming book and I need help analyzing it via gdb

He has the following:

Code:

 while (cards_read < NUM_CARDS) {
     bad_card = false;

     printf("Enter a card: ");

     rank_ch = getchar();

When gdb gets to rank_ch = getchar(), how do I pass a value (9s for 9 of spades for example) into gdb?

full source code: http://knking.com/books/c2/programs/poker.c

**Salem** · 08-01-2020

Have you tried pressing 9 and then enter?

**rusyoldguy** · 08-03-2020

Hallo bos1234!

I hope this code can help you, ignore the german comments.

Code:

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 4 -*-  */
/*
 * main.cc
 * 
 * chkkeystroke is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * chkkeystroke is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>
#include <termios.h>

#include <fcntl.h>

struct termios orig_termios;

void reset_terminal_mode()
{
    tcsetattr(0, TCSANOW, &orig_termios);
}

void set_conio_terminal_mode()
{
    struct termios new_termios;

    /* take two copies - one for now, one for later */
    tcgetattr(0, &orig_termios);
    memcpy(&new_termios, &orig_termios, sizeof(new_termios));

    /* register cleanup handler, and set the new terminal mode */
    atexit(reset_terminal_mode);
    cfmakeraw(&new_termios);
    tcsetattr(0, TCSANOW, &new_termios);
}

int kbhit()
{
    struct timeval tv = { 0L, 0L };
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(0, &fds);
    return select(1, &fds, NULL, NULL, &tv);
}

// normaly 1, but better ch, so we have the ASCII-value;
int xkbhit(void)
{
  struct termios oldt, newt;
  int ch;
  int oldf;
 
  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);
 
  ch = getchar();
 
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);
 
  if(ch != EOF)
  {
    ungetc(ch, stdin);
    return ch;// Normaly return value  1, here the ASCII-value 
  }
 
  return 0;
}

/// reads from keypress, doesn't echo
int getch(){
    struct termios oldt, newt;
    int ch;
    tcgetattr( STDIN_FILENO, &oldt );
    newt = oldt;
    newt.c_lflag &= ~( ICANON | ECHO );
    tcsetattr( STDIN_FILENO, TCSANOW, &newt );
    ch = getchar();
    tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
    return ch;
}

int own_getstring(char wort[])
{
 int rewer = 0, taste = 0, i = 0; 

  while ((taste == 10) || (taste == 13))
    {
     taste = xkbhit(); 

     if ((taste == 10) || (taste == 13))
      {        
       rewer = 1;
       } 
       else  
        {
         wort[i++] = (char)taste;
         wort[i] = '\0';   
        }    
    }

 return rewer;    
}

int main(int argc, char *argv[])
{
  int taste = 0, i = 0;
    char wort[200] = {0};
    //set_conio_terminal_mode(); // Wenn nicht gesetzt dann bei gedrueckter Enter-Taste 
/*                               // with xkbhit returnvalue 10, if set then 13
while (!xkbhit())
    {}
       printf("%c", taste);        
    */

   for (i = 0; i < 20; i++)    
    {
     while (taste == 0)
      taste = xkbhit(); 
      usleep(100000); //<--------------------you can modify these number, try and see  
     printf("%c", taste);  
     taste = 0; 
   }     
    

    printf("***%c = %d    i=%d\n", taste, taste, i);
   //taste = own_getstring(wort);
   //printf("Enter was: %s\n", wort);

getch();
    printf("Program end\n");

    
    return EXIT_SUCCESS;
    
}

It was written for SUSE Linux tumbleweed, but i hope, it can help you.

**rusyoldguy** · 08-03-2020

other example:

Code:

/* getchar example : typewriter */
#include <stdio.h>

int main(int argc, char **argv)
{
  int c;
  puts ("Enter text. Include a dot ('.') in a sentence to exit:");
  do {
    c=getchar();
    putchar (c);
  } while (c != '.');
  return 0;
}

here the second better version of the source above:

Code:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>
#include <termios.h>
 
#include <fcntl.h>
 
struct termios orig_termios;
 
void reset_terminal_mode()
{
    tcsetattr(0, TCSANOW, &orig_termios);
}
 
void set_conio_terminal_mode()
{
    struct termios new_termios;
 
    /* take two copies - one for now, one for later */
    tcgetattr(0, &orig_termios);
    memcpy(&new_termios, &orig_termios, sizeof(new_termios));
 
    /* register cleanup handler, and set the new terminal mode */
    atexit(reset_terminal_mode);
    cfmakeraw(&new_termios);
    tcsetattr(0, TCSANOW, &new_termios);
}
 
int kbhit()
{
    struct timeval tv = { 0L, 0L };
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(0, &fds);
    return select(1, &fds, NULL, NULL, &tv);
}
 
// normaly return value is 1, but better ch, so we have the ASCII-value;
int xkbhit(void)
{
  struct termios oldt, newt;
  int ch;
  int oldf;
  
  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);
  
  ch = getchar();
  
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);
  
  if(ch != EOF)
  {
    ungetc(ch, stdin);
    return ch; // Normaly return value  1, here the ASCII-value 
  }
  
  return 0;
}
 
/// reads from keypress, doesn't echo
int getch(){
    struct termios oldt, newt;
    int ch;
    tcgetattr( STDIN_FILENO, &oldt );
    newt = oldt;
    newt.c_lflag &= ~( ICANON | ECHO );
    tcsetattr( STDIN_FILENO, TCSANOW, &newt );
    ch = getchar();
    tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
    return ch;
}
 
int own_getstring(char wort[])
{
 int rewer = 0, taste = 0, i = 0; 
 
  for (i = 0; i < 100; i++)
  { 
   while (taste == 0) taste = xkbhit(); 
   usleep(180000); //<--------------------you can modify these number, try and see    
   taste = getch();
   
   if ((taste == 10) || (taste == 13))
    return i;
     
   printf("%c", taste);  
   wort[i] = (char)taste;
   wort[i + 1] = '\0';   
  }
 
 return rewer;    
}
 
int main(int argc, char *argv[])
{
  int taste = 0, i = 0;
    char wort[200] = {0};
    //set_conio_terminal_mode(); // if not set then returnvalue by Enter-button with xkbhit returnvalue 10, if set then 13
 
   for (i = 0; i < 20; i++)    
    {
     while (taste == 0) taste = xkbhit(); 
      taste = getch(); 
      usleep(180000); //<--------------------you can modify these number, try and see  
      if (taste == 10) break;
     printf("%c", taste);  
     wort[i] = taste;
     taste = 0; 
   }     
     
 
   printf("\nfirst Enter was: %s\n", wort);
   taste = own_getstring(wort);
   printf("\nsecond Enter was: %s\ni=%dn", wort, taste);
 
   getch();
   
   printf("Program end\n");
 
   return EXIT_SUCCESS;
}

Thread: how to pass values into getchar in gdb

Thread Tools

Search Thread

Display

how to pass values into getchar in gdb

Similar Threads

How to pass values to a dateTimePicker control

How to pass enum values

Pass values to C++ dll and return result

howto pass values to & from

Tags for this Thread