warning C code (connection to Mysql db)

Question

I get some annoying warnings while trying to connect to a Mysql db.

Here's the code:

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <mysql/mysql.h>
#include <string.h>

const char* host = "localhost";
char *database="Dbis_RG";
char user_name[10];
char passwd[10];

MYSQL_ROW row;
MYSQL_RES* result;
MYSQL_FIELD* field;

int main ()
{

    system("clear");


    printf("Insert yur user name: \n");
    scanf("%s", &user_name);

    printf("Insert your passwd: \n");
    scanf("%s", &passwd);


    MYSQL *conn;

   conn = mysql_init(NULL);


    /* Connection to database */
      if (!mysql_real_connect(conn, host,
            user_name, passwd, database, 0, NULL,CLIENT_MULTI_STATEMENTS)) {
            fprintf(stderr, "%s\n", mysql_error(conn));
            exit(EXIT_SUCCESS);
            } 



        printf ("Connection successful.\n");


}

As a matter of fact I get these warnings, but I don't see how I could get rid of them:

1.0.c: In function ‘main’:
1.0.c:23: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[10]’
1.0.c:26: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[10]’

Thank you very much

Mauro

Hello @Mauro ! We are so excited that you are participating in Stack Overflow. However, we've noticed that you have asked us several questions in the past but have not accepted any answers. Will you go back and accept some answers to your previous questions? You can do this by clicking the green checkmark. — rlb.usa
– rlb.usa, Commented Sep 14, 2011 at 21:48

sidyll · Accepted Answer · 2011-09-14 21:51:32Z

3

You could do it like this:

scanf("%s", user_name);
scanf("%s", passwd);

But it's not a good idea. Use fgets instead. Check your manual page. And for further details, try to make people motivated to answer your questions.

answered Sep 14, 2011 at 21:51

sidyll

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3 Comments

Margherita Over a year ago

thanks for your answer. It actually works, but you say that's not a good idea..does that mean it's not ansi C?..If I use fgets does that solve the problem the same way? thanks

Pete Wilson Over a year ago

@Mauro -- please read what @ Tomer already said and fix your mistake! He didn't say it wasn't ansi C; he said what you wrote was a security hole and was dangerous.

thang Over a year ago

also, if you don't want to use fgets, you can limit the # of bytes scanf reads by doing %9s (no space) or %9c (with space) to read only 9 characters, so scanf("%9s", user_name);

Tomer Vromen · Accepted Answer · 2011-09-14 21:53:47Z

2

What brain said.
You're using scanf() in a non-safe way - if my name is more than 10 characters long (or if I just want to break your program) the scanf() call will overflow beyond the array. Use scanf("%9s", user_name); instead (I think you need to leave room for the '\0' at the end).

answered Sep 14, 2011 at 21:53

Tomer Vromen

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Comments

brain · Accepted Answer · 2013-01-10 06:46:34Z

0

username and passwd are already arrays, so you should get rid of the "&" when using scanf.

edited Jan 10, 2013 at 6:46

answered Sep 14, 2011 at 21:50

brain

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3 Comments

brain Over a year ago

Call them what you want. They are memory addresses :)

pmg Over a year ago

@brain: you should read section 6 of the c-faq. And once you're there, read the other sections too :P

brain Over a year ago

@pmg: The point is the function expects a pointer, and that's what it gets in that respect. Even if the argument passed is an array. Now, changed my answer as not to confuse people. :p

Margherita · Accepted Answer · 2011-09-15 22:06:13Z

-1

I solved the problem by using strlen...I check the input through strlen and if it's greater than the specified array size a suitable warning prevents the user to carry on...Do you think it's a good idea ?

answered Sep 15, 2011 at 22:06

Margherita

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1 Comment

pmg Over a year ago

No! After the scanf, if more characters were read than the space reserved for them, the harm is already done. You cannot undo the harm with a warning.

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