On an international web site, what would be a suitable length for the following entries:
-First name or Christian name
-Second name or middle name
-Surname or last name
-Street and number
-Town or city
This is required for the CGI that will handle the results of the HTML form since the data cannot be truncated and the format of the file that will hold the data has to be decided accordingly.

The main concern is for example some Asian names are extremely long compared to Westen ones.
Is there anyone with this sort of experience who can provide advice?

Thank you for your help.

What about using variable length strings in your file format ?

This means reading the whole file when a member makes a change like a change of address. It also means if the new info supplied by the member is longer than the old one it won't fit and would have to be relocated.
We prefer simplicity over saving a bit of disk space.

what file ?
You mean you haven't set a database or an ldap directory to store user's entries ?

That is correct. It's not "users" I am talking about, it is "members" and it is not a database but a flat file but we're getting away from the subject. The choice between a database or a flat file was made a long time ago.

.

As a non native english speaker, I'm not going argue about semantics but I'm still quite sure these international site members are also this site's users ...

Anyway, it is certainly possible to have variable lenght names stored in flat files: CSVs, GEDCOM, XML and the likes do it easily, in fact fixed length data files is the exception.
The initial choice to have fixed lenght fields was a wrong design decision, and trying to figure out what other arbitrary maximum lenght is to be decided is probably still a wrong decision, unless you set an urealistic high mark (i.e. 256 characters for each field), which may hurts if your members count is in the million zone.
You may also need to set some string length limits in your CGIs to prevent buffer overflow attacks, depending on the back-end programming language.

Pour quelqu'un dont la langue maternelle n'est pas l'anglais, votre anglais est parfait et vous n'auriez pas de difficultés a discuter les moindres détails.

Nous ne sommes pas une organisation commerciale et cela implique beaucoup de changements en ce qui concerne les coutumes de logiciels, parfois nous devons faire l'opposé de ce qui serait fait normalement.

Cependant, nous avons des difficultés a introduire un système de sécurité et il est possible qu'a la suite de cela, nous allons changer ce fichier en zones de longueur variables. Pas mal d'autres points doivent être discutés avant.

Ceci ne me fait pas abandonner mon idée de trouver, si possible, quelqu'un qui a de l'expérience en ce qui concerne ma question.

Je vous remercie pour vos commentaires qui sont définitivement valables et ne sont pas ignorés.

Your French is not bad too
Thanks !