1. Complete c program for beginners is here:
http://manishtech.wordpress.com/2009/03/30/sqlite-with-c/
2. sqlite3_exec with callback is an obsolete concept from sqlite2
Use sqlite3_prepare_v2 with sqlite3_step as it is linear, more effective and
giving more control approach.
I hope it helps,
Samuel
________________________________
From: noel frankinet <noel.franki...@skynet.be>
To: General Discussion of SQLite Database <sqlite-users@sqlite.org>
Sent: Tue, January 19, 2010 9:18:06 AM
Subject: Re: [sqlite] Need help understanding the basic of C++/sqlite
Fabrice NA a écrit :
Hi,
In sqlite3_exec, you pass a function pointer (callback).
Sqlite call that function with each row of data
Best wishes
Noël
> 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?
>
>
>
> 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;
>
>
>
> 1) What is the purpose of doing "sqlite3 *db" are we just creating a
> pointer of type sqlite3 named db here?
>
>
>
> 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? 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?
>
>
>
> 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.
>
>
>
> 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).
>
>
>
> 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++?
>
>
>
> 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
> _______________________________________________
> sqlite-users mailing list
> sqlite-users@sqlite.org
> http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
>
>
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