Question

I am writing a function to prepare a sql query and execute it against a sqlite db. I am using a query to insert values in to a table, the query looks like this

   "insert into files values (?, ?, ?, ?, ?, 0)";

A row is inserted but all values for text fields are empty except the last field which is 0. The first 5 fields are of type TEXT

    // If I hard code a value for value.data() then the row is inserted correctly with my hardcoded data, the exact line is below
    status = sqlite3_bind_text(ppStmt, index, /* if I hardcode it works*/ value.data(), -1, SQLITE_STATIC);

The full function is shown below.The list is created on stack by the calller, I am not sure why it is not replacing question marks with my string args, hardcoded ones work though.. no error codes are returned

    //db is already open before I call this
void MediaCache::prepareAndExecuteQuery(string query, list<string> args)
{

    sqlite3_stmt *ppStmt = 0;
    const char **pzTail = 0;
    int status = 0;

    if( sqlite3_prepare_v2(db, query.data(), query.length(), &ppStmt, pzTail) != SQLITE_OK )
    {
        string error = sqlite3_errmsg(db);
        //throw an exception
    } 

    if(ppStmt)
    {

        list<string>::iterator current = args.begin();
        int index = 1;

        for(current = args.begin() ; current != args.end(); current++)
        {
            string value = *current;            
            status = sqlite3_bind_text(ppStmt, index, value.data(), -1, SQLITE_STATIC);

            if(status != SQLITE_OK)
            {
                //log error;
            }

            index++;
        }   

        status = sqlite3_step(ppStmt);
        status = sqlite3_finalize(ppStmt);
        //sqlite3_exec(db, "COMMIT", NULL, NULL, NULL);
    }
    else
    {
        //ppStmt is null
        //throw an exception
    }

}

Answer 1

I suspect the problem is here:

string value = *current;            
status = sqlite3_bind_text(ppStmt, index, value.data(), -1, SQLITE_STATIC);

In this case value goes out of scope before the execution of the statement takes place. So the pointers given to sqlite3_bind_text are no longer valid. To “fix” that, you could use SQLITE_TRANSIENT, which would force the library to make its own copy of the data before returning.

Also, if you are not using C++11, I don’t believe string::data() is guaranteed to be NULL terminated in which case the -1 parameter could be incorrect. It should maybe be value.length() instead.