Question

Hi I wrote a simple c prog to just accept a password while diplaying * to hide the input. But the * for the last character entered is not appearing at the right place.
the code is below

int main(){  
int choice = 0;  
char pass[8];  
FILE *input;  
FILE *output;  
struct termios initial_settings, new_settings;  

if(!isatty(fileno(stdout))){  
    fprintf(stderr,"Not a terminal \n");  
}  
input = fopen("/dev/tty","r");  
output = fopen("/dev/tty","w");  
if(!input || !output){  
fprintf(stderr,"error opening");  
exit(1);  
}  
tcgetattr(fileno(input),&initial_settings);  
new_settings = initial_settings;  
new_settings.c_lflag &= ~ICANON;  
new_settings.c_lflag &= ~ECHO;  
new_settings.c_cc[VMIN] = 1;  
new_settings.c_cc[VTIME] = 0;  
new_settings.c_lflag &= ~ISIG;  
if(tcsetattr(fileno(input), TCSANOW, &new_settings) != 0) {  
fprintf(stderr,"could not set attributes\n");  
}

int count = 0;  
char ch;  
printf("Please enter the password: ");  
while (count<8){  
ch = fgetc(input);  

if(ch == '\n' || ch == '\r'){  
break;  
}else{  
fputc('*',stdout);  
pass[count] = ch;  
count++;  
}  
tcdrain(fileno(stdout));  
}  


fprintf(output,"you have entered :%s \n",pass);  
tcsetattr(fileno(input),TCSANOW,&initial_settings);  
exit(0);  
}  

The output is as follows:
Please enter the password:* * * * * * *
you have entered :12345678
* pasman@pasman-laptop:~$

Its an 8 character password & Notice that 7 *s appear as expected but the last * is appearing at the end of main.

Answer 1

You’re mixing stdio and another stream, output, talking directly to the tty. They have different buffers, and get flushed at different times. You really should just use one of them.