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prepared_statement.cpp example crashes
Posted by: Mateusz Karbowy
Date: September 20, 2009 06:55PM

Hi. I'm running MySQL 5.1 GA Community Server. I've downloaded the source code for C++ connector (v1.05) and successfully compiled it under VS 2008. Now, when I run prepared_statement.cpp example that was included with the connector's sources it simply crashes. I've tried downloading pre-compiled connector, but it's the same. I havent tried running other examples, cuz I basically wanted to see how prepared statements work and no joy.

Also, I dont understand why there are 2 lines with the same code in your example:

stmt.reset(emulate_prepare_execute(con, string("USE " + database).c_str()));
stmt.reset(emulate_prepare_execute(con, string("USE " + database).c_str()));

I'd appreciate some response, I'm considering using MySQL in my project, but at the moment I'm stuck, cause I cannot even see an example file working properly...
Here's the source code for your prepared_statement.cpp and I marked with XXX comments where it crashes (note: I havent altered the example file):

/*
Copyright 2007 - 2008 MySQL AB, 2008 - 2009 Sun Microsystems, Inc. All rights reserved.

The MySQL Connector/C++ is licensed under the terms of the GPL
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html, like most
MySQL Connectors. There are special exceptions to the terms and
conditions of the GPL as it is applied to this software, see the
FLOSS License Exception
http://www.mysql.com/about/legal/licensing/foss-exception.html.
*/

/**
* Example of statements - not to be confused with prepared statements
*
* NOTE: The MySQL Server does not support each and every SQL statement
* to be prepared. The list of statements which can be prepared is available
* in the MySQL Server documentation and the C API documentation:
* http://dev.mysql.com/doc/refman/5.1/en/c-api-prepared-statements.html
* (Link to the MySQL Server 5.1 documentation!)
*
* Connector/C++ is based on the C API and C library "libmysql". Therefore
* it inherits all limitations from the MySQL Server and the MySQL C API.
*
* MySQL 5.1.12 can prepare the following statements:
*
* - CREATE TABLE, DELETE, DO, INSERT, REPLACE, SELECT, SET, UPDATE
* - most SHOW commands
* - ANALYZE TABLE, OPTIMIZE TABLE, REPAIR TABLE
* - CACHE INDEX, CHANGE MASTER, CHECKSUM {TABLE | TABLES},
* - {CREATE | RENAME | DROP} DATABASE, {CREATE | RENAME | DROP} USER
* - FLUSH {TABLE | TABLES | TABLES WITH READ LOCK | HOSTS | PRIVILEGES | LOGS | STATUS | MASTER | SLAVE | DES_KEY_FILE | USER_RESOURCES}
* - GRANT, REVOKE, KILL, LOAD INDEX INTO CACHE, RESET {MASTER | SLAVE | QUERY CACHE}
* - SHOW BINLOG EVENTS, SHOW CREATE {PROCEDURE | FUNCTION | EVENT | TABLE | VIEW}
* - SHOW {AUTHORS | CONTRIBUTORS | WARNINGS | ERRORS}
* - SHOW {MASTER | BINARY} LOGS, SHOW {MASTER | SLAVE} STATUS
* - SLAVE {START | STOP}, INSTALL PLUGIN, UNINSTALL PLUGIN
*
* ... that's pretty much every *core* SQL statement - but not USE as you'll see below.
*
* Connector/C++ does not include a prepared statement emulation
*
* @link http://dev.mysql.com/doc/refman/5.1/en/c-api-prepared-statements.html
*/

/* Standard C++ includes */
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <stdexcept>

/*
Public interface of the MySQL Connector/C++.
You might not use it but directly include directly the different
headers from cppconn/ and mysql_driver.h + mysql_util.h
(and mysql_connection.h). This will reduce your build time!
*/
#include <driver/mysql_public_iface.h>
/* Connection parameter and sample data */
#include "examples.h"

bool prepare_execute(std::auto_ptr< sql::Connection > & con, const char *sql);
sql::Statement* emulate_prepare_execute(std::auto_ptr< sql::Connection > & con, const char *sql);

using namespace std;

int main(int argc, const char **argv)
{
static const string url(argc >= 2 ? argv[1] : EXAMPLE_HOST);
static const string user(argc >= 3 ? argv[2] : EXAMPLE_USER);
static const string pass(argc >= 4 ? argv[3] : EXAMPLE_PASS);
static const string database(argc >= 5 ? argv[4] : EXAMPLE_DB);

/* Driver Manager */
sql::Driver *driver;
/* sql::ResultSet.rowsCount() returns size_t */
size_t row;
stringstream sql;
stringstream msg;
int i, num_rows;

cout << boolalpha;
cout << "1..1" << endl;;
cout << "# Connector/C++ prepared statement example.." << endl;

try {
/* Using the Driver to create a connection */
driver = get_driver_instance();
std::auto_ptr< sql::Connection > con(driver->connect(url, user, pass));

/* The usage of USE is not supported by the prepared statement protocol */
std::auto_ptr< sql::Statement > stmt(con->createStatement());
stmt->execute("USE " + database);

/*
Prepared statement are unhandy for queries which you execute only once!

prepare() will send your SQL statement to the server. The server
will do a SQL syntax check, perform some static rewriting like eliminating
dead expressions such as "WHERE 1=1" and simplify expressions
like "WHERE a > 1 AND a > 2" to "WHERE a > 2". Then control gets back
to the client and the server waits for execute() (or close()).
On execute() another round trip to the server is done.

In case you execute your prepared statement only once - like shown below -
you get two round trips. But using "simple" statements - like above - means
only one round trip.

Therefore, the below is *bad* style. WARNING: Although its *bad* style,
the example program will continue to do it to demonstrate the (ab)use of
prepared statements (and to prove that you really can do more than SELECT with PS).
*/
std::auto_ptr< sql::PreparedStatement > prep_stmt(con->prepareStatement("DROP TABLE IF EXISTS test"));
prep_stmt->execute();

prepare_execute(con, "CREATE TABLE test(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, label CHAR(1))");
cout << "#\t Test table created" << endl;

/*
The first useful example - prepare() once, execute() n + 1 times
NOTE: The MySQL Server does not support named parameters. You have to use
the placeholder syntax shown below. There is no emulation which would you
allow to use named parameter like ':param1'. Use '?'. Parameters are 1-based.
*/
num_rows = 0;
prep_stmt.reset(con->prepareStatement("INSERT INTO test(id, label) VALUES (?, ?)"));
for (i = 0; i < EXAMPLE_NUM_TEST_ROWS; i++) {
prep_stmt->setInt(1, test_data.id);
prep_stmt->setString(2, test_data.label);
/* executeUpdate() returns the number of affected = inserted rows */
num_rows += prep_stmt->executeUpdate();
}

if (EXAMPLE_NUM_TEST_ROWS != num_rows) {
msg.str("");
msg << "Expecting " << EXAMPLE_NUM_TEST_ROWS << "rows, reported " << num_rows;
throw runtime_error(msg.str());
}
cout << "#\t Test table populated" << endl;

/* We will reuse the SELECT a bit later... */
std::auto_ptr< sql::PreparedStatement > prep_select(con->prepareStatement("SELECT id, label FROM test ORDER BY id ASC"));
cout << "#\t Running 'SELECT id, label FROM test ORDER BY id ASC'" << endl;
std::auto_ptr< sql::ResultSet > res(prep_select->executeQuery());
row = 0;
while (res->next()) {
cout << "#\t\t Row " << row << " - id = " << res->getInt("id");
cout << ", label = '" << res->getString("label") << "'" << endl;
row++;
}
res.reset(NULL);

if (EXAMPLE_NUM_TEST_ROWS != row) {
msg.str("");
msg << "Expecting " << EXAMPLE_NUM_TEST_ROWS << "rows, reported " << row;
throw runtime_error(msg.str());
}

cout << "#\t Simple PS 'emulation' for USE and another SELECT" << endl;
stmt.reset(emulate_prepare_execute(con, string("USE " + database).c_str())); // XXX - it gives a "first-chance exception"
stmt.reset(emulate_prepare_execute(con, string("USE " + database).c_str())); // XXX - it gives a "first-chance exception"

stmt.reset(emulate_prepare_execute(con, "SELECT id FROM test ORDER BY id ASC"));
res.reset(stmt->getResultSet());
if (res.get() != NULL) {
row = 0;
while (res->next()) {
cout << "#\t\t Row " << row << " - id = " << res->getInt("id") << endl;
row++;
}
res.reset(NULL);
}
stmt.reset(NULL);

/* Running the SELECT again but fetching in reverse order */
cout << "#\t SELECT and fetching in reverse order" << endl;

res.reset(prep_select->executeQuery()); // XXX - it crashes here
row = res->rowsCount();
cout << "#\t\t res->getRowsCount() = " << res->rowsCount() << endl;
if (res->rowsCount() != EXAMPLE_NUM_TEST_ROWS) {
msg.str("");
msg << "Expecting " << EXAMPLE_NUM_TEST_ROWS << "rows, found " << res->rowsCount();
throw runtime_error(msg.str());
}

/* Position the cursor after the last row */
cout << "#\t\t Position the cursor after the last row\n";
res->afterLast();
cout << "#\t\t res->isafterLast()\t= " << res->isAfterLast() << endl;
cout << "#\t\t res->isLast()\t\t= " << res->isLast() << endl;
if (!res->isAfterLast() || res->isLast())
throw runtime_error("Moving the cursor after the last row failed");

while (res->previous()) {
cout << "#\t\t res->previous()\n";
cout << "#\t\t Row " << row << " - id = " << res->getInt("id");
cout << ", label = '" << res->getString("label") << "'" << endl;
row--;
}
cout << "#\t\t Should be before the first\n";
cout << "#\t\t res->isFirst()\t\t= " << res->isFirst() << endl;
cout << "#\t\t res->isBeforeFirst()\t= " << res->isBeforeFirst() << endl;
if (res->isFirst() || !res->isBeforeFirst())
throw runtime_error("Cursor should be before first row");

/* Now that the cursor is before the first, fetch the first */
cout << "#\t\t Now that the cursor is before the first, fetch the first\n";
cout << "#\t\t calling next() to fetch first row" << endl;
row++;
res->next();
cout << "#\t\t res->isFirst()\t\t= " << res->isFirst() << endl;
cout << "#\t\t Row " << row << " - id = " << res->getInt("id");
cout << ", label = '" << res->getString("label") << "'" << endl;
row--;

/* For more on cursors see resultset.cpp example */

/* Clean up */
res.reset(NULL);
stmt.reset(con->createStatement());
stmt->execute("DROP TABLE IF EXISTS test");
cout << "#done!" << endl;

} catch (sql::SQLException &e) {
/*
The MySQL Connector/C++ throws three different exceptions:

- sql::MethodNotImplementedException (derived from sql::SQLException)
- sql::InvalidArgumentException (derived from sql::SQLException)
- sql::SQLException (derived from std::runtime_error)
*/
cout << endl;
cout << "# ERR: DbcException in " << __FILE__;
cout << "(" << __FUNCTION__ << ") on line " << __LINE__ << endl;
/* Use what(), getErrorCode() and getSQLState() */
cout << "# ERR: " << e.what();
cout << " (MySQL error code: " << e.getErrorCode();
cout << ", SQLState: " << e.getSQLState() << " )" << endl;

if (e.getErrorCode() == 1047) {
/*
Error: 1047 SQLSTATE: 08S01 (ER_UNKNOWN_COM_ERROR)
Message: Unknown command
*/
cout << "# ERR: Your server seems not to support PS at all because its MYSQL <4.1" << endl;
}
cout << "not ok 1 - examples/prepared_statement.cpp" << endl;

return EXIT_FAILURE;
} catch (std::runtime_error &e) {

cout << endl;
cout << "# ERR: runtime_error in " << __FILE__;
cout << "(" << __FUNCTION__ << ") on line " << __LINE__ << endl;
cout << "# ERR: " << e.what() << endl;
cout << "not ok 1 - examples/prepared_statement.cpp" << endl;

return EXIT_FAILURE;
}

cout << "ok 1 - examples/prepared_statement.cpp" << endl;
return EXIT_SUCCESS;
}


bool prepare_execute(std::auto_ptr< sql::Connection > & con, const char *sql)
{
sql::PreparedStatement * prep_stmt;

prep_stmt = con->prepareStatement(sql);
prep_stmt->execute();
delete prep_stmt;

return true;
}


sql::Statement* emulate_prepare_execute(std::auto_ptr< sql::Connection > & con, const char *sql)
{
sql::PreparedStatement *prep_stmt;
sql::Statement *stmt = NULL;

cout << "#\t\t 'emulation': " << sql << endl;

try {

prep_stmt = con->prepareStatement(sql);
prep_stmt->execute();
cout << "#\t\t 'emulation': use of sql::PreparedStatement possible" << endl;
/* safe upcast - PreparedStatement is derived from Statement */
stmt = prep_stmt;

} catch (sql::SQLException &e) {
/*
Maybe the command is not supported by the MySQL Server?

http://dev.mysql.com/doc/refman/5.1/en/error-messages-server.html
Error: 1295 SQLSTATE: HY000 (ER_UNSUPPORTED_PS)

Message: This command is not supported in the prepared statement protocol yet
*/

if (e.getErrorCode() != 1295) {
// The MySQL Server should be able to prepare the statement
// but something went wrong. Let the caller handle the error.
throw ;
}
cout << "#\t\t 'emulation': ER_UNSUPPORTED_PS and fallback to sql::Statement" << endl;
cout << "#\t\t ERR: " << e.what();
cout << " (MySQL error code: " << e.getErrorCode();
cout << ", SQLState: " << e.getSQLState() << " )" << endl;

stmt = con->createStatement();
stmt->execute(sql);
}

return stmt;
}



Edited 5 time(s). Last edit at 09/21/2009 08:20PM by Mateusz Karbowy.

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