getpass and strcmp in c

[thebloggu]

void registo(){

char nome_utilizador[20];

char *password;

int a;

char *password_conf; //confirm password

while(getchar()!='\n');

printf("What name do you want to use? ");

fgets(nome_utilizador,20,stdin);

password = getpass("What password do you want to use? ");

password_conf = getpass("Please confirm the password:: ");

a = strcmp(password,password_conf);

if(strcmp(password,password_conf)!=0){

printf("Congratulations you successfully registeres in the program\n");

login();

}

else{

printf("Passwords dont match please try again\n");

registo();

}

}

i have this but strcmp doesnt work even though the words are equal. what's the problem?

[mike_g]

strcmp returns 0 if the two word match. So you should be doing:

if(strcmp(password,password_conf)==0){
// password matches

[scourge]

strcmp returns 0 when the strings are equal.

So, replace this:

if(strcmp(password,password_conf)!=0)

with this:

if (strcmp(password,password_conf) == 0)

[thebloggu]

LOL

sorry, i tried just

if(strcmp(password,password_conf)){

without == or != because i thought it was by default ==. i tried ==0 and it worked thank you

[sq377]

sudo apt-get install manpges-dev manpages-posix-dev
man getpass

"DESCRIPTION
This function is obsolete. Do not use it.
"

If you want to avoid it, here is a function I used to implement it a while back:


...
#include <termios.h>
....
char *password = 0;
....
if (password == NULL)
{
#ifdef _GNU_SOURCE // Other operating systems hide terminals differently

struct termios normal, hidden;

tcgetattr(fileno(stdin), &normal);
hidden = normal;
hidden.c_lflag &= ~ECHO || ECHOCTL;
tcsetattr(fileno(stdin), TCSAFLUSH, &hidden); // Terminal is hidden

#endif // _GNU_SOURCE

printf("Password: ");
password = calloc(100, sizeof(char));
password[strlen(password + 1)] = '\0';
fgets(password, 99, stdin);
for (x = 0; x <= 100; x++)
{
if (password[x] == '\n')
password[x] = '\0';
if (password[x] == '\0')
break;
}

#ifdef _GNU_SOURCE
printf("\n");
tcsetattr(fileno(stdin), TCSAFLUSH, &normal);
fflush(stdin);
fflush(stdout);
#endif // _GNU_SOURCE
}

[mike_g]

password = calloc(100, sizeof(char));
Personally I would not allocate memory when you know the container size (100). Also, your code never frees the memory once its done with it which could cause memory leaks. Since calloc zeros the memory theres no need for this line:

password[strlen(password + 1)] = '\0';
And instead of this:

for (x = 0; x <= 100; x++)
{
if (password[x] == '\n')
password[x] = '\0';
if (password[x] == '\0')
break;
}
You could just do:

if(strlen(password) < 100)
password[strlen(password)-1]='\0';

Apart from that the termios bit looks interesting, I have never seen it myself yet. Might have a play around with the code ;)

[smartbei]

You will actually want:


password[strlen(password) - 2] = '\0';

Since strlen(password) returns the length including the \n...In order to remove the \n you have to subtract one for the array being zero-indexed and one to delete the \n.

EDIT: This is wrong - as mike_g shows below. (Sorry, my mistake)

[mike_g]

Sorry, but I think you are wrong. Using your method the following code outputs 'Hel':

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

int main()
{
char word[] = "Hello";
word[strlen(word)-2]='\0';
printf("%s", word);
return 0;
}

[smartbei]

Ouch!
That was bad...

[thebloggu]

thank you, i solved my problem.

now i am trying to serach for a string in a file using


int procura_string_na_bd(char *nick){

char str[100]; //linha

FILE *registos; //declara bd como ficheiro

registos = fopen( "registos.bd", "r" ); // abre ficheiro em bd

if( registos != NULL ){ // se bd != vazio continua

while (fgets(str,sizeof(str),registos)!=NULL){ //lê linha a linha do ficheiro

if (strstr(str,nick)!=NULL) //verifica se uma string existe dentro de outra
return 1; //verdade

}

}

return 0; //falso

}

the problem is that if i search in "AAAA AB" for B it finds it but it shouldn't. so i have to find string and not amount of characters

[mike_g]

Yes, thats normal behavior for strstr, as it looks for any match within the string. A better way to go about parsing the file may be to split each line using strtok, go to the column/word position that the password should be at then compare it to your password using strcmp.

[thebloggu]

problem is i don't know how to use strtok. searched for informations but it seems to return only one string while in my case it should retrieve 2.

[thebloggu]

should not this work?


int procura(char palavra[10]){

char linha[100];

char nome[10],pass[10];

FILE *bd;

bd = fopen("bd.txt","r");

if(bd!=NULL){

fgets(linha,sizeof(linha),bd);

sscanf(linha,"%s,%s\n",nome,pass);

if(strcmp(nome,palavra)==1)
return 1;

else return 0;

}

return 0;
}

it returns segmentation fail

[mike_g]

The problem with sscanf is that you need spaces to delimit your strings for example, say theline in your file is:

myuserame,mypassword
And you try parse it like you are doing:

sscanf(linha,"%s,%s\n",nome,pass);
The first %s wont know where to stop reading as the ',' would be counted as par of the string. Another disadvantage to this is that your names and passwords cant have spaces in them. You should be able to get it to work by adding some spaces IE:

username , password

sscanf(linha,"%s %*c %s\n", nome, pass);
but tbh I reckon you would be best off learning how to use strtok, as you can set your own delimeters with it.

[thebloggu]

got it to work, now the problem is that i have my file in


name,pass

this format. but still, for example i look for 'anana' it says it is there even thoug it is 'banana'.

[mike_g]

How did you get it to work? Are you still using strstr? strcmp won't return 0 comparing two strings that don't match.

If you're bent on using strstr on your file I guess you could get it to work something like:

char temp_str[100];
strcpy(temp_str, ",");
strcat(temp_str, password_entered);
strcat(temp_str, "\n");
if(strstr(temp_str, password_file_line))
password is good

But its pretty ugly, and will break with the slightest inconsistency in your password file.

[thebloggu]

well i reworked my code and it is something like


char clean_nl(char compara[50]){

int a;

a = strlen(compara);

if(compara[a]=='\n')
strncpy(compara,compara,a-1);

printf("%s",compara);

return compara[50];

}


int procura(char palavra[50],FILE *ficheiro,char *delimit){

char linha[100];

char *token = NULL;

char compara[50];

printf("1\n");

if(ficheiro==NULL){

printf("Erro de leitura, tente novamente\n");

return 0;

}

else{

printf("2\n");

while(fgets(linha,sizeof(linha),ficheiro)!=NULL){

printf("3\n");

token = strtok(linha,delimit);

while(token!=NULL){//enquanto houver qualquer no token

clean_nl(compara);

printf("4\n");

printf("%s\n",token);

sprintf(compara,"%s",token);

printf("%s\n",palavra);

printf("%s\n",compara);

if(strcmp(compara,palavra) == 1 && strlen(compara) == strlen(palavra))
return 1;

token = strtok(NULL,delimit);

}

return 0;

}

}

return 0;

}



int main(){

char *palavra;

FILE *ficheiro;

char *delimit;

int a;

delimit = ",";

palavra = "ola";

ficheiro = fopen("ficheiro.a","r");

a = procura(palavra,ficheiro,delimit);

if(a==1)
printf("existe\n");

else printf("nao existe\n");

return 0;

}

but it is not working, almost. btw how do i return a string in clean_nl?