Passing Pointers - Dev Shed

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October 11th, 2002, 06:30 PM

Beans4You

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Passing Pointers

I'm trying to implement a BerkleyDB database. It works if I declare the Db inside a single function but it blows up on me if I try to implement it in a class and try to pass the Db to the function. The OS that I'm working on is Win2K and the compiler is VC++ 6.0. The BerkleyDB download and white pages can be found at www.sleepycat.com.

Here is the code that works:

Code:

void createdb_pc(char* DATABASE_PC){
	Db dbp_pc(0, 0);
	dbp_pc.set_error_stream(&cerr);
	dbp_pc.set_errpfx("AccessExample");
	dbp_pc.set_pagesize(1024);		/* Page size: 1K. */
	dbp_pc.set_cachesize(0, 32 * 1024, 0);
	dbp_pc.open(NULL, DATABASE_PC, NULL, DB_BTREE, DB_CREATE, 0664);
}

Here is the code that I tried to get to work:

Code:

Private:
Db dbDatabase(0, 0);

void createdb_pc(Db *dbp_pc, char* DATABASE_PC){
 	dbp_pc.set_error_stream(&cerr);
	dbp_pc.set_errpfx("AccessExample");
	dbp_pc.set_pagesize(1024);		/* Page size: 1K. */
	dbp_pc.set_cachesize(0, 32 * 1024, 0);
	dbp_pc.open(NULL, DATABASE_PC, NULL, DB_BTREE, DB_CREATE, 0664);
}

Public:

myClas(){
	createdb_pc(dbDatabase, "data001.db");
}

Now I get a "Constant" error when on the dbDatabase(0, 0) and the compiler gives me another error stating that I need a struct on the right hand side set_error_stream, set_errpfx, set_page,...

Any help would be greatly appreciated.

Eric

October 11th, 2002, 07:47 PM

StealthElephant

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why are u initializing db inside the class private segment?
i haven't ever used that but i can tell straignt away that that definitely wont work

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October 11th, 2002, 09:00 PM

Beans4You

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I have another header file that needs to call this header to record the information that it gathers. All that I need is to have an instance of the Db class that I can pass into the function createdb_pc.

My idea was to have the Db declared in this class so that the constructor would create-open the database and the destructor would close the database, and until the class is destroyed I can write to the database. I have also tried to create an instance of the class inside of another function and then pass that to createdb_pc, but it also crashes.

October 12th, 2002, 01:38 AM

StealthElephant

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Re: Passing Pointers

Quote:

Originally posted by Beans4You

Code:

void createdb_pc(char* DATABASE_PC){ Db dbp_pc(0, 0); dbp_pc.set_error_stream(&cerr); dbp_pc.set_errpfx("AccessExample"); dbp_pc.set_pagesize(1024); /* Page size: 1K. */ dbp_pc.set_cachesize(0, 32 * 1024, 0); dbp_pc.open(NULL, DATABASE_PC, NULL, DB_BTREE, DB_CREATE, 0664); }

Here is the code that I tried to get to work:

Code:

Private: Db dbDatabase(0, 0); void createdb_pc(Db *dbp_pc, char* DATABASE_PC){ dbp_pc.set_error_stream(&cerr); dbp_pc.set_errpfx("AccessExample"); dbp_pc.set_pagesize(1024); /* Page size: 1K. */ dbp_pc.set_cachesize(0, 32 * 1024, 0); dbp_pc.open(NULL, DATABASE_PC, NULL, DB_BTREE, DB_CREATE, 0664); } Public: myClas(){ createdb_pc(dbDatabase, "data001.db"); }

Eric

thats a syntax error when u try to do that with db, put that code inside a class method
Db dbDatabase(0, 0);

October 12th, 2002, 06:59 AM

Beans4You

Some day I will be a Lambda!

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I'm sorry for wasting everyone's time. I got some sleep and then looked at it and wanted to slap myself. I don't need to worry about the Db handle, I just need to pass in the name of the database file, the key, and data field. It's to easy... I was making it way to hard. Thanks for everyone's help. Here is the code if anyone would like to see.

Code:

void dbWrite(char* DATABASE, char* KEY,char* DATA){
	Db dbp(0, 0);
	int ret;

	dbp.set_error_stream(&cerr);
	dbp.set_errpfx("AccessExample");
	dbp.set_pagesize(1024);		/* Page size: 1K. */
	dbp.set_cachesize(0, 32 * 1024, 0);
	dbp.open(NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664);

	Dbt key(KEY,sizeof(KEY));
	Dbt data(DATA,sizeof(DATA));
	
	ret = dbp.put(0, &key, &data, DB_NOOVERWRITE);
	if (ret == DB_KEYEXIST) {
		cout << "Key " << KEY << " already exists.\n";
	}
	
	dbp.close(0);
}

Thanks again.

Eric

October 16th, 2002, 09:24 AM

pajo

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In your code:

void createdb_pc(Db *dbp_pc, char* DATABASE_PC){
dbp_pc.set_error_stream(&cerr);
...
}

you pass pointer to Db (dbp_pc), and dereference it as a class (dot member). You shoud either pass buy reference:

void createdb_pc(Db& dbp_pc, char* DATABASE_PC){
dbp_pc.set_error_stream(&cerr);
...
}

or use -> to dereference:

void createdb_pc(Db *dbp_pc, char* DATABASE_PC){
dbp_pc->set_error_stream(&cerr);
...
}

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