Weird *char change with sqlite3_step(statement) - iphone

Question

WIth this code I'm trying to get SQL CREATE statement from sqlite_master for a specific table:
[SQLStatement setString:#"SELECT name, sql FROM sqlite_master WHERE type='table' AND name='"];
[SQLStatement appendString:tableName];
[SQLStatement appendString:#"'"];
int dbrc;
const char *charSQLStatement = [SQLStatement UTF8String];
sqlite3_stmt *statement = nil;
dbrc = sqlite3_prepare_v2 (dbHandleSQLite, charSQLStatement, -1, &statement, NULL);
const char *nameColumn,*sqlColumn;
dbrc = sqlite3_step (statement);
NSString *tempString;
do {
nameColumn = sqlite3_column_text(statement,0);
sqlColumn = sqlite3_column_text(statement,1);
NSLog(#"%s",nameColumn);
NSLog(#"%s",sqlColumn);
tempString = [NSString stringWithCString:sqlColumn encoding:NSASCIIStringEncoding];
} while (sqlite3_step(statement) == SQLITE_ROW);
sqlite3_finalize (statement);
NSLog(#"%s",nameColumn);
NSLog(#"%s",sqlColumn);
do-while loop is run through only once. You can see, that I have made a small workaround to get this worked and assigned value to tempString.
Reason is because if sqlite3_step(statement) is ran again, nameColumn and sqlColumn change their values although not being called again??!!
nameColumn is firt assigned the name of the table and sqlColumn is assigned "CREATE TABLE..." statement, which is OK.
But when program comes to while sentence, nameColumn changes to "index" and sqlColumn to something non-understandable, although loop is not repeated.
How can this happen? What am I doing wrong?

Answer 1

You're not doing anything wrong. sqlite reuses buffers. If you want to keep something you get from it, make a copy of it: a pointer's value is only guaranteed until the next sqlite3_step or sqlite3_finalize.
So your workaround is how you're supposed to handle this.
From the sqlite docs:
The pointers returned are valid until a type conversion occurs as described above, or until sqlite3_step() or sqlite3_reset() or sqlite3_finalize() is called. The memory space used to hold strings and BLOBs is freed automatically. Do not pass the pointers returned sqlite3_column_blob(), sqlite3_column_text(), etc. into sqlite3_free().