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I want to mask my password while writing it with *.
I use Linux GCC for this code.
I know one solution is to use getch() function like this
#include <conio.h>
int main()
{
char c,password[10];
int i;
while( (c=getch())!= '\n');{
password[i] = c;
printf("*");
i++;
}
return 1;
}
but the problem is that GCC does not include conio.h file so, getch() is useless for me.
Does anyone have a solution?
In the Linux world, masking isn't usually done with asterisks, normally echoing is just turned off and the terminal displays blanks E.g. if you use su or log into a virtual terminal etc.
There is a library function to handle getting passwords, it won't mask the password with asterisks but will disable echoing of the password to terminal. I pulled this out of a linux book I have. I believe its part of the posix standard
#include <unistd.h>
char *getpass(const char *prompt);
/*Returns pointer to statically allocated input password string
on success, or NULL on error*/
The getpass() function first disables echoing and all processing of
terminal special characters (such as the interrupt character, normally
Control-C).
It then prints the string pointed to by prompt, and reads a line of
input, returning the null-terminated input string with the trailing
newline stripped, as its function result.
A google search for getpass() has a reference to the GNU implementation (should be in most linux distros) and some sample code for implementing your own if need be
http://www.gnu.org/s/hello/manual/libc/getpass.html
Their example for rolling your own:
#include <termios.h>
#include <stdio.h>
ssize_t
my_getpass (char **lineptr, size_t *n, FILE *stream)
{
struct termios old, new;
int nread;
/* Turn echoing off and fail if we can't. */
if (tcgetattr (fileno (stream), &old) != 0)
return -1;
new = old;
new.c_lflag &= ~ECHO;
if (tcsetattr (fileno (stream), TCSAFLUSH, &new) != 0)
return -1;
/* Read the password. */
nread = getline (lineptr, n, stream);
/* Restore terminal. */
(void) tcsetattr (fileno (stream), TCSAFLUSH, &old);
return nread;
}
If need be you could use this as the basis as modify it to display asterisks.
Without getch to rely on and avoiding the obsolete getpass, the recommended approach is to disable terminal ECHO through termios use. After a few searches to find a canned flexible password routine, I was surprised that very few for stand-alone use with C. Rather than simply recoding getch with termios c_lflag options, slightly more generalized approach takes just a few additions. Beyond replacing getch any routine should enforce a specified maximum length to prevent overflow, truncate if the user attempt to enter beyond the maximum, and warn if truncation occurs in some manner.
Below, the additions will allow reading from any FILE * input stream, limiting the length to a specified length, provide minimal editing (backspace) ability when taking input, allow the character mask to be specified or disabled completely, and finally return the length of the password entered. A warning was added when the password entered was truncated to the maximum or specified length.
Hopefully it will prove useful to others with this question looking for a similar solution:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#define MAXPW 32
/* read a string from fp into pw masking keypress with mask char.
getpasswd will read upto sz - 1 chars into pw, null-terminating
the resulting string. On success, the number of characters in
pw are returned, -1 otherwise.
*/
ssize_t getpasswd (char **pw, size_t sz, int mask, FILE *fp)
{
if (!pw || !sz || !fp) return -1; /* validate input */
#ifdef MAXPW
if (sz > MAXPW) sz = MAXPW;
#endif
if (*pw == NULL) { /* reallocate if no address */
void *tmp = realloc (*pw, sz * sizeof **pw);
if (!tmp)
return -1;
memset (tmp, 0, sz); /* initialize memory to 0 */
*pw = (char*) tmp;
}
size_t idx = 0; /* index, number of chars in read */
int c = 0;
struct termios old_kbd_mode; /* orig keyboard settings */
struct termios new_kbd_mode;
if (tcgetattr (0, &old_kbd_mode)) { /* save orig settings */
fprintf (stderr, "%s() error: tcgetattr failed.\n", __func__);
return -1;
} /* copy old to new */
memcpy (&new_kbd_mode, &old_kbd_mode, sizeof(struct termios));
new_kbd_mode.c_lflag &= ~(ICANON | ECHO); /* new kbd flags */
new_kbd_mode.c_cc[VTIME] = 0;
new_kbd_mode.c_cc[VMIN] = 1;
if (tcsetattr (0, TCSANOW, &new_kbd_mode)) {
fprintf (stderr, "%s() error: tcsetattr failed.\n", __func__);
return -1;
}
/* read chars from fp, mask if valid char specified */
while (((c = fgetc (fp)) != '\n' && c != EOF && idx < sz - 1) ||
(idx == sz - 1 && c == 127))
{
if (c != 127) {
if (31 < mask && mask < 127) /* valid ascii char */
fputc (mask, stdout);
(*pw)[idx++] = c;
}
else if (idx > 0) { /* handle backspace (del) */
if (31 < mask && mask < 127) {
fputc (0x8, stdout);
fputc (' ', stdout);
fputc (0x8, stdout);
}
(*pw)[--idx] = 0;
}
}
(*pw)[idx] = 0; /* null-terminate */
/* reset original keyboard */
if (tcsetattr (0, TCSANOW, &old_kbd_mode)) {
fprintf (stderr, "%s() error: tcsetattr failed.\n", __func__);
return -1;
}
if (idx == sz - 1 && c != '\n') /* warn if pw truncated */
fprintf (stderr, " (%s() warning: truncated at %zu chars.)\n",
__func__, sz - 1);
return idx; /* number of chars in passwd */
}
A simple program showing the use would be as follows. If using a static array of character for holding the password, just insure a pointer is passed to the function.
int main (void ) {
char pw[MAXPW] = {0};
char *p = pw;
FILE *fp = stdin;
ssize_t nchr = 0;
printf ( "\n Enter password: ");
nchr = getpasswd (&p, MAXPW, '*', fp);
printf ("\n you entered : %s (%zu chars)\n", p, nchr);
printf ( "\n Enter password: ");
nchr = getpasswd (&p, MAXPW, 0, fp);
printf ("\n you entered : %s (%zu chars)\n\n", p, nchr);
return 0;
}
Example Output
$ ./bin/getpasswd2
Enter password: ******
you entered : 123456 (6 chars)
Enter password:
you entered : abcdef (6 chars)
The functionality of getch (which is a non-standard, Windows function) can be emulated with this code:
#include <termios.h>
#include <unistd.h>
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;
}
Note that your approach is not perfect - it's better to use something like ncurses or another terminal library to handle these things.
You can create your own getch() function on Linux in this manner.
int getch() {
struct termios oldtc, 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;
}
Demo code:
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;
}
Your method is correct, however you'll need to turn off terminal echo while the password is being entered:
#include <sgtty.h>
void echo_off()
{
struct sgttyb state;
(void)ioctl(0, (int)TIOCGETP, (char *)&state);
state.sg_flags &= ~ECHO;
(void)ioctl(0, (int)TIOCSETP, (char *)&state);
}
void echo_on()
{
struct sgttyb state;
(void)ioctl(0, (int)TIOCGETP, (char *)&state);
state.sg_flags |= ECHO;
(void)ioctl(0, (int)TIOCSETP, (char *)&state);
}
Instead of getch(), why not just use getc() instead?
Thanks all of you whose help & support to solve my problem.
I find a best way to hide my password in linux that fits me best.
To use getpass() function. It just need to include "unistd.h" file.
syntex of getpass function:
char * getpass (const char *prompt)
Parameters:
prompt: string pointer to print while asking for Password
Return Value:
string pointer of password
Example:
#include <stdio.h>
#include <unistd.h>
int main()
{
char *password; // password string pointer
password = getpass("Enter Password: "); // get a password
printf("%s\n",password); // this is just for conformation
// that password stored successfully
return 1;
}
output:
Enter Password:
heet
You might use ncurses.h if it is not necessary to be portable onto Windows for that, but here is some kind of a more "portable" version:
If it is not necessery to be portable ill point you to a ncurses solution
portablegetch.h
/*portablegetch.h*/
#ifndef PGETCH
#define PGETCH
#ifdef __unix__
#include <termios.h>
#include <unistd.h>
static struct termios n_term;
static struct termios o_term;
static int
cbreak(int fd)
{
if((tcgetattr(fd, &o_term)) == -1)
return -1;
n_term = o_term;
n_term.c_lflag = n_term.c_lflag & ~(ECHO|ICANON);
n_term.c_cc[VMIN] = 1;
n_term.c_cc[VTIME]= 0;
if((tcsetattr(fd, TCSAFLUSH, &n_term)) == -1)
return -1;
return 1;
}
int
getch()
{
int cinput;
if(cbreak(STDIN_FILENO) == -1) {
fprintf(stderr, "cbreak failure, exiting \n");
exit(EXIT_FAILURE);
}
cinput = getchar();
tcsetattr(STDIN_FILENO, TCSANOW, &o_term);
return cinput;
}
#elif _MSC_VER || __WIN32__ || __MS_DOS__
#include <conio.h>
#endif
#endif
And the c-file
whatever.c
#include <stdio.h>
#include <stdlib.h>
#include "portablegetch.h"
int
main(int argc, char **argv)
{
int input;
printf("Please Enter your Password:\t");
while(( input=getch() ) != '\n')
printf("*");
printf("\n");
return EXIT_SUCCESS;
}
That should fit to your problem.
Hope that helps.
#include <termios.h>
#include <stdio.h>
static struct termios old, new;
void initTermios(int echo) {
tcgetattr(0, &old);
new = old;
new.c_lflag &= ~ICANON;
new.c_lflag &= echo ? ECHO : ~ECHO;
tcsetattr(0, TCSANOW, &new);
}
void resetTermios(void) {
tcsetattr(0, TCSANOW, &old);
}
char getch_(int echo) {
char ch;
initTermios(echo);
ch = getchar();
resetTermios();
return ch;
}
char getch(void) {
return getch_(0);
}
int main(void) {
char c;
printf("(getch example) please type a letter...");
c = getch();
printf("\nYou typed: %c\n", c);
return 0;
}
Just copy these snippet and use it. Hope it helped
Just pass for it the char* that you want to set password in and its size and the function will do its job
void set_Password(char *get_in, int sz){
for (int i = 0; i < sz;) {
char ch = getch();
if (ch == 13) {
get_in[i] = '\0';
break;
}
else if(ch != 8){
get_in[i++] = ch;
putch('*');
}
else if(i > 0)
cout << "\b \b",get_in[i--] = '\0';
}
cout << "\n";
}
This is an example, run it on your compiler
Unfortunately in the C standard library there is no such function out of the box. Maybe in third party library.
One option is use ANSI escape sequences to set the background color to foreground color in the console to conceal the password. Try this link.
With scanning the characters you can take it into a buffer. Also you need to write code if backspace is pressed, and appropriately correct the inserted password.
Here is a code which once i wrote with the curses. Compile with gcc file.c -o pass_prog -lcurses
#include <stdio.h>
#include <stdlib.h>
#include <curses.h>
#define ENOUGH_SIZE 256
#define ECHO_ON 1
#define ECHO_OFF 0
#define BACK_SPACE 127
char *my_getpass (int echo_state);
int main (void)
{
char *pass;
initscr ();
printw ("Enter Password: ");
pass = my_getpass (ECHO_ON);
printw ("\nEntered Password: %s", pass);
refresh ();
getch ();
endwin ();
return 0;
}
char *my_getpass (int echo_state)
{
char *pass, c;
int i=0;
pass = malloc (sizeof (char) * ENOUGH_SIZE);
if (pass == NULL)
{
perror ("Exit");
exit (1);
}
cbreak ();
noecho ();
while ((c=getch()) != '\n')
{
if (c == BACK_SPACE)
{
/* Do not let the buffer underflow */
if (i > 0)
{
i--;
if (echo_state == ECHO_ON)
printw ("\b \b");
}
}
else if (c == '\t')
; /* Ignore tabs */
else
{
pass[i] = c;
i = (i >= ENOUGH_SIZE) ? ENOUGH_SIZE - 1 : i+1;
if (echo_state == ECHO_ON)
printw ("*");
}
}
echo ();
nocbreak ();
/* Terminate the password string with NUL */
pass[i] = '\0';
endwin ();
return pass;
}
In C you can use getpasswd() function which pretty much doing similar thing as stty in shell, example:
#include <stdio.h>
#include <string.h>
#include <pwd.h>
#include <unistd.h>
int main()
{
char acct[80], password[80];
printf(“Account: “);
fgets(acct, 80, stdin);
acct[strlen(acct)-1] = 0; /* remove carriage return */
strncpy(password, getpass(“Password: “), 80);
printf(“You entered acct %s and pass %s\n”, acct, password);
return 0;
}
Here is equivalent shell script which use stty (which changes the settings of your tty):
save_state=$(stty -g)
/bin/echo -n “Account: “
read acct
/bin/echo -n “Password: “
stty -echo
read password # this won’t echo
stty “$save_state”
echo “”
echo account = $acct and password = $password
Source: How can I read a password without echoing it in C?
man getpass
This function is obsolete. Do not use it. If you want to read input
without terminal echoing enabled, see the description of the ECHO flag
in termios(3)
# include <termios.h>
# include <unistd.h> /* needed for STDIN_FILENO which is an int file descriptor */
struct termios tp, save;
tcgetattr( STDIN_FILENO, &tp); /* get existing terminal properties */
save = tp; /* save existing terminal properties */
tp.c_lflag &= ~ECHO; /* only cause terminal echo off */
tcsetattr( STDIN_FILENO, TCSAFLUSH, &tp ); /* set terminal settings */
/*
now input by user in terminal will not be displayed
and cursor will not move
*/
tcsetattr( STDIN_FILENO, TCSANOW, &save); /* restore original terminal settings */
If you notice, most current linux distro's do not mask a password with asterisks. Doing so divulges the length of the password which is no way beneficial. It is easier and better to simply make the cursor not move when a password is typed in. If for whatever reason you require a * to be printed for every character that's typed then you would have to grab every keypress before Enter is hit and that's always been problematic.
printf("\nENTER PASSWORD: ");
while (1)
{
ch=getch();
if(ch==13) //ON ENTER PRESS
break;
else if(ch==8) //ON BACKSPACE PRESS REMOVES CHARACTER
{
if(i>0)
{
i--;
password[i]='\0';
printf("\b \b");
}
}
else if (ch==32 || ch==9) //ON PRESSING TAB OR SPACE KEY
continue;
else
{
password[i]=ch;
i++;
printf("*");
}
}
password[i]='\0';
Here is my idea, adapted from that of the C++ official site.
#include <termios.h>
#include <unistd.h>
#include <stdio.h>
#include <iostream>
#include <string>
using namespace std;
string getpass(const char *prompt, bool showchar = false, char echochar = '*')
{
struct termios oi, ni;
tcgetattr(STDIN_FILENO, &oi);
ni = oi;
ni.c_lflag &= ~(ICANON | ECHO);
const char DELETE = 127;
const char RETURN = 10;
string password;
unsigned char ch = 0;
cout << prompt;
tcsetattr(STDIN_FILENO, TCSANOW, &ni);
while (getchar() != RETURN) {
if (ch == DELETE) {
if(password.length != 0){
if (showchar) cout << "\b \b";
password.resize(password.length() - 1);
}
}else {
password += getchar();
if (showchar) cout << echochar;
}
}
tcsetattr(STDIN_FILENO,TCSANOW,&oi)
cout << endl;
return password;
}
It will read one character at once and add it to the string and supports showing another character.
note that the ICANON termios lflag turns off the processing carriagereturn/linefeed, and the negative ECHO termios setting turns off echo for STDIN.
when using this (with or without the echo being on) to read a password and print '*' for entered characters, it's not just a matter of reading characters until a newline/carriage return is encountered, you also have to process backspace in your 'string building routine' (else the backspaces end up in the actual string, and do not cause characters to be removed from it such as would be the case with the various string based input functions).
the same would happen in C in DOS with getch tho. that would also happily return 0x08 for backspace (or 127 or whatever your specific os uses as backspace)
keeping track of 'not deleting -before- the start of the string', replacing the 'new end of the string' with 0 and moving the current position counter back by one (unless you are at position 0) is up to the programmer with any of these functions (even the getch on dos C).
getpass() doesn't do what the user originally asked for btw, he wants *'s (which still disclose the length of the password to people standing behind him and looking at his screen, as well as in the scrollbuffer of the terminal if he doesn't close it after use). but without *'s is probably a better idea in 'non closed environments'.
I've a small C-program which just reads numbers from stdin, one at each loop cycle. If the user inputs some NaN, an error should be printed to the console and the input prompt should return again. On input of "0", the loop should end and the number of given positive/negative values should be printed to the console. Here's the program:
#include <stdio.h>
int main()
{
int number, p = 0, n = 0;
while (1) {
printf("-> ");
if (scanf("%d", &number) == 0) {
printf("Err...\n");
continue;
}
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
My problem is, that on entering some non-number (like "a"), this results in an infinite loop writing "-> Err..." over and over. I guess it's a scanf() issue and I know this function could be replace by a safer one, but this example is for beginners, knowing just about printf/scanf, if-else and loops.
I've already read the answers to the questionscanf() skips every other while loop in C and skimmed through other questions, but nothing really answer this specific problem.
scanf consumes only the input that matches the format string, returning the number of characters consumed. Any character that doesn't match the format string causes it to stop scanning and leaves the invalid character still in the buffer. As others said, you still need to flush the invalid character out of the buffer before you proceed. This is a pretty dirty fix, but it will remove the offending characters from the output.
char c = '0';
if (scanf("%d", &number) == 0) {
printf("Err. . .\n");
do {
c = getchar();
}
while (!isdigit(c));
ungetc(c, stdin);
//consume non-numeric chars from buffer
}
edit: fixed the code to remove all non-numeric chars in one go. Won't print out multiple "Errs" for each non-numeric char anymore.
Here is a pretty good overview of scanf.
scanf() leaves the "a" still in the input buffer for next time. You should probably use getline() to read a line no matter what and then parse it with strtol() or similar instead.
(Yes, getline() is GNU-specific, not POSIX. So what? The question is tagged "gcc" and "linux". getline() is also the only sensible option to read a line of text unless you want to do it all by hand.)
I think you just have to flush the buffer before you continue with the loop. Something like that would probably do the job, although I can't test what I am writing from here:
int c;
while((c = getchar()) != '\n' && c != EOF);
Due to the problems with scanf pointed out by the other answers, you should really consider using another approach. I've always found scanf way too limited for any serious input reading and processing. It's a better idea to just read whole lines in with fgets and then working on them with functions like strtok and strtol (which BTW will correctly parse integers and tell you exactly where the invalid characters begin).
Rather than using scanf() and have to deal with the buffer having invalid character, use fgets() and sscanf().
/* ... */
printf("0 to quit -> ");
fflush(stdout);
while (fgets(buf, sizeof buf, stdin)) {
if (sscanf(buf, "%d", &number) != 1) {
fprintf(stderr, "Err...\n");
} else {
work(number);
}
printf("0 to quit -> ");
fflush(stdout);
}
/* ... */
I had similar problem. I solved by only using scanf.
Input "abc123<Enter>" to see how it works.
#include <stdio.h>
int n, num_ok;
char c;
main() {
while (1) {
printf("Input Number: ");
num_ok = scanf("%d", &n);
if (num_ok != 1) {
scanf("%c", &c);
printf("That wasn't a number: %c\n", c);
} else {
printf("The number is: %d\n", n);
}
}
}
On some platforms (especially Windows and Linux) you can use fflush(stdin);:
#include <stdio.h>
int main(void)
{
int number, p = 0, n = 0;
while (1) {
printf("-> ");
if (scanf("%d", &number) == 0) {
fflush(stdin);
printf("Err...\n");
continue;
}
fflush(stdin);
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
The Solution: You need to add fflush(stdin); when 0 is returned from scanf.
The Reason: It appears to be leaving the input char in the buffer when an error is encountered, so every time scanf is called it just keeps trying to handle the invalid character but never removing it form the buffer. When you call fflush, the input buffer(stdin) will be cleared so the invalid character will no longer be handled repeatably.
You Program Modified: Below is your program modified with the needed change.
#include <stdio.h>
int main()
{
int number, p = 0, n = 0;
while (1) {
printf("-> ");
if (scanf("%d", &number) == 0) {
fflush(stdin);
printf("Err...\n");
continue;
}
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
try using this:
if (scanf("%d", &number) == 0) {
printf("Err...\n");
break;
}
this worked fine for me... try this..
the continue statement is not appropiate as the Err.. should only execute once. so, try break which I tested... this worked fine for you.. i tested....
When a non-number is entered an error occurs and the non-number is still kept in the input buffer. You should skip it. Also even this combination of symbols as for example 1a will be read at first as number 1 I think you should also skip such input.
The program can look the following way.
#include <stdio.h>
#include <ctype.h>
int main(void)
{
int p = 0, n = 0;
while (1)
{
char c;
int number;
int success;
printf("-> ");
success = scanf("%d%c", &number, &c);
if ( success != EOF )
{
success = success == 2 && isspace( ( unsigned char )c );
}
if ( ( success == EOF ) || ( success && number == 0 ) ) break;
if ( !success )
{
scanf("%*[^ \t\n]");
clearerr(stdin);
}
else if ( number > 0 )
{
++p;
}
else if ( number < n )
{
++n;
}
}
printf( "\nRead %d positive and %d negative numbers\n", p, n );
return 0;
}
The program output might look like
-> 1
-> -1
-> 2
-> -2
-> 0a
-> -0a
-> a0
-> -a0
-> 3
-> -3
-> 0
Read 3 positive and 3 negative numbers
I had the same problem, and I found a somewhat hacky solution. I use fgets() to read the input and then feed that to sscanf(). This is not a bad fix for the infinite loop problem, and with a simple for loop I tell C to search for any none numeric character. The code below won't allow inputs like 123abc.
#include <stdio.h>
#include <ctype.h>
#include <string.h>
int main(int argc, const char * argv[]) {
char line[10];
int loop, arrayLength, number, nan;
arrayLength = sizeof(line) / sizeof(char);
do {
nan = 0;
printf("Please enter a number:\n");
fgets(line, arrayLength, stdin);
for(loop = 0; loop < arrayLength; loop++) { // search for any none numeric charcter inisde the line array
if(line[loop] == '\n') { // stop the search if there is a carrage return
break;
}
if((line[0] == '-' || line[0] == '+') && loop == 0) { // Exculude the sign charcters infront of numbers so the program can accept both negative and positive numbers
continue;
}
if(!isdigit(line[loop])) { // if there is a none numeric character then add one to nan and break the loop
nan++;
break;
}
}
} while(nan || strlen(line) == 1); // check if there is any NaN or the user has just hit enter
sscanf(line, "%d", &number);
printf("You enterd number %d\n", number);
return 0;
}
To solve partilly your problem I just add this line after the scanf:
fgetc(stdin); /* to delete '\n' character */
Below, your code with the line:
#include <stdio.h>
int main()
{
int number, p = 0, n = 0;
while (1) {
printf("-> ");
if (scanf("%d", &number) == 0) {
fgetc(stdin); /* to delete '\n' character */
printf("Err...\n");
continue;
}
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
But if you enter more than one character, the program continues one by one character until the "\n".
So I found a solution here: How to limit input length with scanf
You can use this line:
int c;
while ((c = fgetc(stdin)) != '\n' && c != EOF);
// all you need is to clear the buffer!
#include <stdio.h>
int main()
{
int number, p = 0, n = 0;
char clearBuf[256]; //JG:
while (1) {
printf("-> ");
if (scanf("%d", &number) == 0) {
fgets(stdin, 256, clearBuf); //JG:
printf("Err...\n");
continue;
}
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
Flush the input buffer before you scan:
while(getchar() != EOF) continue;
if (scanf("%d", &number) == 0) {
...
I was going to suggest fflush(stdin), but apparently that results in undefined behavior.
In response to your comment, if you'd like the prompt to show up, you have to flush the output buffer. By default, that only happens when you print a newline. Like:
while (1) {
printf("-> ");
fflush(stdout);
while(getchar() != EOF) continue;
if (scanf("%d", &number) == 0) {
...
Hi I know this is an old thread but I just finished a school assignment where I ran into this same problem.
My solution is that I used gets() to pick up what scanf() left behind.
Here is OP code slightly re-written; probably no use to him but perhaps it will help someone else out there.
#include <stdio.h>
int main()
{
int number, p = 0, n = 0;
char unwantedCharacters[40]; //created array to catch unwanted input
unwantedCharacters[0] = 0; //initialzed first byte of array to zero
while (1)
{
printf("-> ");
scanf("%d", &number);
gets(unwantedCharacters); //collect what scanf() wouldn't from the input stream
if (unwantedCharacters[0] == 0) //if unwantedCharacters array is empty (the user's input is valid)
{
if (number > 0) p++;
else if (number < 0) n++;
else break; /* 0 given */
}
else
printf("Err...\n");
}
printf("Read %d positive and %d negative numbers\n", p, n);
return 0;
}
I've recently been through the same problem, and I found a solution that might help a lot of people. The function "scanf" leaves a buffer in memory ... and that's why the infinite loop is caused. So you actually have to "store" this buffer to another variable IF your initial scanf contains the "null" value. Here's what I mean:
#include <stdio.h>
int n;
char c[5];
int main() {
while (1) {
printf("Input Number: ");
if (scanf("%d", &n)==0) { //if you type char scanf gets null value
scanf("%s", &c); //the abovementioned char stored in 'c'
printf("That wasn't a number: %s\n", c);
}
else printf("The number is: %d\n", n);
}
}
I want to have user press the space key to jump out of the while loop.
For example:
while ( some condition )
{
printf ("Press space bar to continue...");
}
Thanks!!
I think you mean the following as long as a spacebar followed by the enter key is acceptable given your comments above.
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
scanf("%c",&input);
}
Or if you prefer, without hitting the enter key:
#include <stdio.h>
int main(int argc, char **argv)
{
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
input = getch();
}
}
This worked on my msysgit bash shell. BUT, some people will insist that it work on Linux as well. Which is fine I guess, I love Linux, but I said the above solution worked on msysgit. The following works on my, let me be specific, Oracle VM for Ubuntu 10.10.
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
int main(int argc, char **argv)
{
char input = 0;
while( input != ' ' )
{
printf("Press space bar to continue...\n");
input = mygetch();
}
}
int mygetch(void)
{
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;
}
The mygetch came from here.
Capturing keystrokes under most platforms requires you to access the console directly. Typically there are libraries available to help you with that. Low-level libraries are termcap (which is derived from terminal capabilities) libraries. There is a "portable" layer on top of termcap called curses. Linux uses the GNU version which is called ncurses and is actually available on a multitude of platforms.
Curses is extensively documented, you can start a tutorial using
$ man ncurses
Your problem requires steps to initialize the console and set up keystroke reader. There are several ways to achieve your desired effect.
I am posting a working example for you to play with. It shows some basic ideas in curses:
/* file: curses_ex1.c */
#include <stdio.h>
#include <curses.h>
const char rotary[4] = "/-\\|";
int main() {
WINDOW *w;
int i = 0;
w = initscr();
if ( w == NULL ) {
return -1; /* unable to initialize curses */
}
timeout(500); /* do not block */
mvprintw(0, 0, "Press space bar to break out of the loop.");
noecho();
for(i = 0; ; i++) { /* no condition so loops forever */
int c;
mvaddch(0, 42, rotary[i%4]); /* display rotator */
c = getch(); /* get a character */
if ( c == ' ')
break;
if ( c != ERR ) { /* not a space but another valid key */
mvprintw(1, 0, "You need to press a space for me to stop (you pressed `%c')", c);
}
}
endwin();
return 0;
}
To compile it:
cc -o curses_ex1 curses_ex1.c -lcurses
Make a variable x = 1, put that in the condition, when they press space bar, set x to 2.
How can I do so that I can display star(*) instead of plain text for password in C++.
I am asking for password and it is plain pass on the screen.
How can I convert them in to star(*) so that user can not see the password while entering.
This is what I have currently
char pass[10]={"test"};
char pass1[10];
textmode(C40);
label:
gotoxy(10,10);
textcolor(3);
cprintf("Enter password :: ");
textcolor(15);
gets(pass1);
gotoxy(10,11);
delay(3000);
if(!(strcmp(pass,pass1)==0))
{
gotoxy(20,19);
textcolor(5);
cprintf("Invalid password");
getch();
clrscr();
goto label;
}
Thanks
You need to use an unbuffered input function, like getch () provided by curses library, or a console library of your OS. Calling this function will return the pressed key character, but will not echo. You can manually print * after you read each character with getch (). Also you need to write code if backspace is pressed, and appropriately correct the inserted password.
Here is a code which once i wrote with the curses. Compile with gcc file.c -o pass_prog -lcurses
#include <stdio.h>
#include <stdlib.h>
#include <curses.h>
#define ENOUGH_SIZE 256
#define ECHO_ON 1
#define ECHO_OFF 0
#define BACK_SPACE 127
char *my_getpass (int echo_state);
int main (void)
{
char *pass;
initscr ();
printw ("Enter Password: ");
pass = my_getpass (ECHO_ON);
printw ("\nEntered Password: %s", pass);
refresh ();
getch ();
endwin ();
return 0;
}
char *my_getpass (int echo_state)
{
char *pass, c;
int i=0;
pass = malloc (sizeof (char) * ENOUGH_SIZE);
if (pass == NULL)
{
perror ("Exit");
exit (1);
}
cbreak ();
noecho ();
while ((c=getch()) != '\n')
{
if (c == BACK_SPACE)
{
/* Do not let the buffer underflow */
if (i > 0)
{
i--;
if (echo_state == ECHO_ON)
printw ("\b \b");
}
}
else if (c == '\t')
; /* Ignore tabs */
else
{
pass[i] = c;
i = (i >= ENOUGH_SIZE) ? ENOUGH_SIZE - 1 : i+1;
if (echo_state == ECHO_ON)
printw ("*");
}
}
echo ();
nocbreak ();
/* Terminate the password string with NUL */
pass[i] = '\0';
endwin ();
return pass;
}
There's nothing in C++ per se to support this. The functions in your example code suggest that you are using curses, or something similar; if so, check the cbreak and nocbreak functions. Once you've called cbreak, it's up to you to echo the characters, and you can echo whatever you like (or nothing, if you prefer).
#include<iostream.h>
#include<conio.h>
#include<stdio.h>
void main()
{
clrscr();
char a[10];
for(int i=0;i<10;i++)
{
a[i]=getch(); //for taking a char. in array-'a' at i'th place
if(a[i]==13) //cheking if user press's enter
break; //breaking the loop if enter is pressed
printf("*"); //as there is no char. on screen we print '*'
}
a[i]='\0'; //inserting null char. at the end
cout<<endl;
for(i=0;a[i]!='\0';i++) //printing array on the screen
cout<<a[i];
sleep(3); //paused program for 3 second
}
Whats an easy way I can store the password the user inputs while still keeping the password hidden?
char password[9];
int i;
printf("Enter your password: ");
for (i=0;i<9;i++)
{
password[i] = getch();
printf("*");
}
for (i=0;i<9;i++)
printf("%c",password[i]);
getch();
}
I wanna store the password so I can do a simple if (password[i] == root_password) so the proper password continues on.
Your problem appears to be that you're not checking for newline '\n' nor end-of-file.
printf("Enter your password: ");
char password[9];
int i;
for (i = 0; i < sizeof password - 1; i++)
{
int c = getch();
if (c == '\n' || c == EOF)
break;
}
password[i] = c;
printf("*");
}
password[i] = '\0';
This way, password will end up being an ASCIIZ string, suitable for printing with puts, printf("%s", password), or - crucially...
if (strcmp(password, root_password)) == 0)
your_wish_is_my_command();
Note that we read at most 8 characters into the password as we need one extra character for the NUL terminator. You could increase that if you wanted.
You need to use the console API in Windows. Below is a snippet that disables echoing in the console window. The function SetConsoleMode() is used to control the echoing (among other things). I save the old mode, so that I can restore the console once the password has been retrieved.
Also, the *ConsoleMode() functions need a handle to the console input buffer. How you can get a handle to these buffers is described in the MSDN documentation of CreateFile().
int main(int argc, char* argv[])
{
char password[100] = { 0 };
printf("Enter your password: ");
HANDLE hConsole = ::CreateFile("CONIN$", GENERIC_WRITE | GENERIC_READ, FILE_SHARE_READ, 0, OPEN_EXISTING, 0, 0);
DWORD dwOldMode;
::GetConsoleMode(hConsole, &dwOldMode);
::SetConsoleMode(hConsole, dwOldMode & ~ENABLE_ECHO_INPUT);
bool bFinished = false;
while(!bFinished) {
if(!fgets(password, sizeof(password) / sizeof(password[0]) - 1, stdin)) {
printf("\nEOF - exiting\n");
} else
bFinished = true;
}
::SetConsoleMode(hConsole, dwOldMode | ENABLE_ECHO_INPUT);
printf("\nPassword is: %s\n", password);
return 0;
}
Since we are in C++ and Windows do this:
#include <iostream>
#include <string>
#include <conio.h> //_getch
#include <Windows.h> //VK_RETURN = 0x0D
using namespace std;
string read_password()
{
string pass;
cout << "Enter your password: ";
int character = 0;
while(VK_RETURN != (character = _getch()) )
{
cout << '*';
pass += static_cast<char>(character);
}
cout << std::endl;
return pass;
}
int main ()
{
string root_password = "anypass123";
string pass = read_password();
if (pass == root_password)
{
cout << "password accepted" << endl;
}
return 0;
}
compiled & tested