From: Thimble Smith
Date: March 22 1999 6:07am
Subject: Re: Why the error here?
List-Archive: http://lists.mysql.com/mysql/757
Message-Id: <19990321230711.R25614@desert.net>
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Thomas,

> char *db = "db";
>
> /* ... */
>
> printf("Enter a name for your new database\n\n"); scanf("%s", &db);

This is a Frequently Asked Question, but for comp.lang.c, not for
this MySQL list.  I highly recommend (read: you must do this; must)
that you read the entire comp.lang.c Frequently Asked Questions list.
Don't just skim it.  Spend a day with it, reading every question over
and over until you understand it.  You will not be sorry you did it;
if you don't understand every question on the FAQ, you WILL make one
of the mistakes (like the one you're making now), and you WON'T know
that you've made it or why what you did is wrong.

The C FAQ is one of the best things for beginning C programmers to
read.  Don't be intimidated by it; print it out, sit down with it
and a GOOD C book, and go through it.

You've actually got several problems in your code.  For one, your
variable db is pointing to a STRING CONSTANT, which is NOT the same
as a character array.  It's pointing to read-only memory, which
means that you can't assign to it.  Second, you're passing scanf
the address of the pointer, not the address of the character array.
So, you're trying to store characters over top of the pointer.  Not
good.

If you look at question 7.1 of the C FAQ, you'll see an example of
how to do what you're trying.  But PLEASE, PLEASE don't just read
that example, cut-n-paste, and then go on making more mistakes like
this.  You MUST read the FAQ; you can't just type things in C and
expect them to work!  You have to know what you're doing!  If you
cut and paste and plow along, you will be writing programs that are
full of bugs, and you might not know it.  You might think they're
working fine, and they're scribbling all over memory (if you're
on a lousy non-protected OS) or they're threatening to dump core at
the slightest provokation.

Do yourself a favor and don't write another line of code in your real
app until you've read through the entire FAQ.  Then start your app
all over again.

Tim

P.S.  After you've read and understood the FAQ, write code for a
week or so.  Then spend another day reading the FAQ again.  You
should read the FAQ every week for at least two months while you're
learning C.  At least once a week!

On Sun, Mar 21, 1999 at 10:20:52PM -0500, Thomas R. Bedell wrote:
> Hello,
> 
> I am trying to use:
> 
> mysql_create_db in a C program.  It compiles and links OK.  But
> when you execute the program, I get the following error.
> 
> #include "mysql.h"
> #include "mysql.h"
> #include <stdio.h>
> #include <stdlib.h>
> 
> MYSQL mysql;
> MYSQL_RES *res;
> MYSQL_ROW row;
> char *db = "db";
> 
> void exiterr(int exitcode)
> {
> fprintf( stderr, "%s\n", mysql_error(&mysql) ); exit( exitcode );
> }
> 
> main()
> {
> char db;
> printf("Enter a name for your new database\n\n"); scanf("%s", &db);
> if (!(mysql_connect(&mysql,"localhost","root",""))) exiterr(1);
> if (mysql_create_db(&mysql, &db))
> exiterr(2);
> 
> mysql_free_result(res);
> mysql_close(&mysql);
> }
> 
> When I run my code here is what I get:
> [root@oscar mysql_c]# ./connect
> Enter a name for your new database
> 
> homes
> Segmentation fault
> BUT....  The database is added to mysql.  I can connect to it,
> and view the "empty set".  Why the segmentation fault???