[prog] Strings in C

[Meredydd Luff]

Another proviso with fgets() - it puts a newline onto the end of any string 
it reads. So, for example:

char mystr[64];

fgets(mystr, 64, stdin);

If I type "Hello" into that program, mystr will look like this:

{'H', 'e', 'l', 'l', 'o', '\n', '\0', ...}

Meredydd

On Friday 18 October 2002 18:38, Diggy Bell wrote:
> A couple of quick C topics...
>
> 1. Strings are represented in C as an array of characters terminated with
> '\0'.  This means that for any string that you use, you will need to
> account for an additional character.  If you want to allow 10 characters,
> you would define the string as follows:
>
>     char myString[11];
>
> The value "TESTING123" would be stored as:
>
> T, E, S, T, I, N, G, 1, 2, 3, \0
>
> 2. Reading user input from stdin doesn't provide a great deal of control.
> If this were a production application, fgets wouldn't be the best option,
> but that probably isn't a concern here.  But, since you're using fgets, you
> might want to use it to limit the number of characters a bit.  The fgets()
> call will also properly \0 terminate your string.
>
>     char email[41]; // the final variable for the email address (include 1
> character for the \0)
>     int email_len; // the length of the string returned
>
>     // print the user message
>     printf("Please enter your email address: ");
>     // make sure fgets doesn't return NULL
>     if(fgets(email, 40, stdin))
>     {
>         email_len = strlen(email); // will always be 40 or less
>     }
>
> Voila!  You should now have a string containing the email address with a
> length of 40 or less.
>
> 3. When your ready to go to the database, it's time to create some SQL.
> Here's the easiest way I can think of at the moment (1st cup of coffee
> still...):
>
>     char sqlstring[512]; // this string is often too large, but you gotta
> allow for it
>
>     sprintf(sqlstring, "insert into mytable (emailaddr) values ('%s');",
> email);
>
> The SQL string is now ready to execute against your PostgreSQL database.
>
> Good luck!
>
> William D. 'Diggy' Bell
> Principal
> DB Software Development
> http://www.dbsoftdev.com
>
> ----- Original Message -----
> From: "Therese Gustafsson" <th_gustafsson at yahoo.com>
> To: <programming at linuxchix.org>
> Sent: Friday, October 18, 2002 2:02 AM
> Subject: [prog] Strings in C
>
> > Hi!
> >
> > I'm trying to write a C-program that accesses a
> > postgresql-database. I'm having trouble with the
> > stringhandling and I'm hoping someone here can help
> > me.
> >
> > I have a short code-example and I'm going to try to
> > explain what my problem is.
> >
> > Here are my variables:
> > char email[256],l_email[40];
> > int email_length;
> >
> > This is where the user input is read in.
> > printf("Input email-address: ");
> > fgets(email, 256, stdin);
> >
> > Now here comes my problem. The email field in the
> > database is only 40 characters long, so now I want to
> > make sure that the email string is max 40 characters
> > long and I don't want the "\0"-character at the end of
> > the string.
> >
> > Here's what I've done. I get the length of the string
> > the user input with strlen. (I don't understand why I
> > have to subtract one, but if I don't the stringlength
> > is one character to long. I thought strlen didn't
> > count the "\0"-character?) Then if the length of the
> > user input is longer than the field in the database I
> > just truncate it.
> > email_length = strlen(email)-1;
> > if (email_length > 40)
> > {
> >         email_length = 40;
> > }
> >
> > Now I copy the user input to another string that's as
> > long as the field in the database. This is to copy all
> > user input except for the "\0".
> > strncpy(l_email,email,email_length);
> >
> > Problem number 1: If the string the user wrote is less
> > then 40 characters the end of the l_email string
> > sometimes contains "junk"-characters. How can I get
> > rid of those? I want the rest of the string empty.
> >
> > Problem number 2: Isn't there an easier way to do
> > this? It seems as if I've made it to complicated.
> >
> > I'm sorry if I haven't explained it so you can
> > understand. English isn't my first language.
> >
> > /Therese
> >
> > __________________________________________________
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