Thanks all for your input.
Thanks to your feedback I have been able to advance quite a long way in my
studies... And yes my big problem is in fact understanding C++ (still in
learning phase).
4) I will check if this option is avaialable too on the express edition.
5) I did try to install System.Data.SQLite last week but it doesn't seem to
be supported in the express edition of the Visual product.
I never came across the Wiki link before even though I spent sometime on
sqlite.org so thanks again for this.
Regards,
Fabou
2010/1/19 Simon Davies <simon.james.dav...@googlemail.com>
> 2010/1/19 Fabrice NA <pazou...@gmail.com>:
> > Hi all,
> >
> > I am trying to understand Sqlite and to make thing worse I am also
> learning
> > C++. You will not be surprised that I find it really hard to understand
> the
> > C++ example on the web. Can someone guide me to digest this? If you can
> > explain please do so by extrapolating since I am a total newbie.
> >
> > I have managed to compile the code example into a file called testdb.exe
> and
> > have created a database named Cars.db containing 7 rows. (notice that I
> have
> > removed some part of that code that I don't need help for)
> >
> > #include <stdio.h>
> > #include <sqlite3.h>
> >
> > static int callback(void *NotUsed, int argc, char **argv, char
> **azColName){
> > int i;
> > for(i=0; i<argc; i++){
> > printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
> > }
> > printf("\n");
> > return 0;
> > }
> >
> > int main(int argc, char **argv){
> > sqlite3 *db;
> > char *zErrMsg = 0;
> > int rc;
> > if( argc!=3 ){
> > fprintf(stderr, "Usage: %s DATABASE SQL-STATEMENT\n", argv[0]);
> > exit(1);
> > }
> >
> > rc = sqlite3_open(argv[1], &db);
> > rc = sqlite3_exec(db, argv[2], callback, 0, &zErrMsg);
> >
> > sqlite3_close(db);
> >
> > return 0;
> >
> > }
> >
> > Now in command line when I execute testdb.exe cars.db "select * from
> cars"
> > (the table is called cars too) everything works fine and I get an output
> > with all my seven rows. But how come this work? Is this some kind of
> magic?
>
> No
>
> >
> > Even after reading the doc again and again I don't understand (probably
> > because I am still learning some basic C++ concepts). Here my questions;
>
> Your problems appear to be mostly understanding C/C++.
>
> >
> > 1) What is the purpose of doing "sqlite3 *db" are we just
> creating a
> > pointer of type sqlite3 named db here?
>
> Yes. It is essentially a handle to the database that is returned by
> the database open call, which then needs to be passed to other sqlite
> library routines.
>
> >
> > 2) At first I though that for the main function the first
> > parameter "cars.db"
> > was represented by the variable argc and the second "select * from cars"
> by
> > argv. Well at the end, it looks like that "cars.db" is argv[1] and that
> the
> > select statement is argv[2]. What is argc then?
>
> argc is the count of passed in arguments
> argv is the vector of passed in arguments
> argv[0] is always the name of the executable that is executing
>
> > Seems like it's the number
> > of rows returned by the query (when looking at function callback) but how
> > the program find this out? How come we have a line " if( argc!=3 )" and
> see
> > this same argc variable in the callback function?
>
> argc/argv in main and argc/argv in callback have nothing to do with each
> other.
>
> callback is a routine that needs to be provided for an sqlite_exec()
> call. In callback argc would be better named numColumns, and argv
> better named columnData.
>
> >
> > 3) I don't understand the third argument from the query " rc =
> > sqlite3_exec(db, argv[2], callback, 0, &zErrMsg);" my problem is
> > understanding the callback function inside the sqlite3_exec function.
> > Reading this link http://www.sqlite.org/c3ref/exec.html didn't help too
> much
> > even though it has been written in plain English.
>
> As sqlite_exec() retrieves each row of data, it calls the callback
> routine that is provided via the third argument (in your case also
> named 'callback'). You can then do what YOU want with the data by
> coding the callback appropriately. In the case you have shown, the
> values are simply being printed out.
>
> >
> > 4) I am using VC++ Express from Microsoft on WinXP and would like
> to
> > know if it's possible to pass parameter when debugging i.e. tell the
> > debugger to use cars.db for file and use "select * from cars" as a
> statement
> > (this would allow me to see what's hapening witout replacing variables by
> > their real values).
>
> Don't know about VC++ Express, but in Visual Studio there is a
> debugging tab on the project properties page that allows command line
> arguments to be specified.
>
> >
> > 5) It's really hard to find some simple example on internet about
> C++
> > working with sqlite. Can any of you provide with simple sample codes that
> > shows how you can do and what you can do with sqlite and C++?
>
> SQLite is a C library, not C++. You can however link C++ code against
> C object, and the SQLite library even provides appropriate 'extern "C"
> {}' wrapping around things so that it can be compiled with a C++
> compiler; but that does not make it C++ code.
>
> There are C++ wrappers, notably System.Data.SQLite
> (http://sqlite.phxsoftware.com)
> (sorry anybody else)
>
> further things to take a look at:
> http://www.sqlite.org/cintro.html
>
> The code you show above is based on sqlite3_exec(). This is
> deprecated; better to use sqlite3_prepare_v2(), sqlite3_step,
> sqlite3_reset()/sqlite3_finalize():
> http://www.sqlite.org/cvstrac/wiki?p=SimpleCode
>
> >
> > I hope I didn't offended anyone with my lack of knowledge and I thank in
> > advance the courageous ones who managed to read this email until the end
> and
> > probably got answers to my questions.
> >
> > Fabou
>
> Regards,
> Simon
> _______________________________________________
> sqlite-users mailing list
> sqlite-users@sqlite.org
> http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
>
_______________________________________________
sqlite-users mailing list
sqlite-users@sqlite.org
http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
