Access instance variable via static method

Question

When I run this :

@interface Database : NSObject {
      sqlite3 *database;
}

+(void)openDatabase;

@end



@implementation Database

+(void)openDatabase
{
    NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString *databaseNameandPath = [NSString stringWithFormat:@"%@/DatabaseSnax.sqlite",docDir];
    NSString *databasePath=[[NSString alloc]initWithFormat:databaseNameandPath];

    if(sqlite3_open([databasePath UTF8String], &database) != SQLITE_OK)
    {
        NSLog(@"Error when open the database");
    }

    [databasePath release];
}

I have this error: instance variable database accessed in class method

How I can solve this issue and I need to keep my method (open database) as a static method so I can use it by class name, for example:

[Database openDatabase];

Answer 1

One cannot possibly access instance variables from class methods. You may declare a global variable, however:

static sqlite3 *database;
// ...
+ (void) openDatabase {
    sqlite3_open(filename, &database);
    // ...
}

Answer 2

You're attempting to access database from a class method (which are different from instance methods).

Change that declaration from:

+ (void) openDatabase;

to

- (void) openDatabase;

and instantiate your Database object via the traditional alloc + init and you'll be on your way.

I like H2CO3's answer too (and +1 to him), but my answer (which is what most people have to do with Objective C objects) may be more practical for what you are trying to do.