How to fix unresolved external symbol due to MySql Connector C++?

Question

I followed this tutorial http://blog.ulf-wendel.de/?p=215#hello. I tried both on Visual C++ 2008 and Visual C++ 2010. Either static or dynamic, the compiler gave me the same

Answer 1

According to MySQL 5.1 Reference Manual if you are using the Version 1.1 of the MySQL Connector C++:
"get_driver_instance() is now only available in dynamic library builds - static builds do not have this symbol. This was done to accommodate loading the DLL with LoadLibrary or dlopen. If you do not use CMake for building the source code you will need to define mysqlcppconn_EXPORTS if you are loading dynamically and want to use the get_driver_instance() entry point."
If I understand the previous note correctly, you have to use the dynamic build and define mysqlcppconn_EXPORTS.

Answer 2

I don't know if you have your heart set on using this MySQL Connector/Driver package but there are many robust database wrappers available for free or nearly free out there if this is causing seemingly unspoken headaches for you.

I actually was thoroughly impressed by QT database objects when I used them previously for a data model project. The QT framework is licensed under LGPL and also has a commercial version available and is a very versatile set of cross platform libraries. The QtSql objects provide a consistent interface to many databases including MySql, SQLServer, Postgres, ODBC, etc with the ability to substitute your own drivers and still use the same interface for everything at a high level in C++

Some other notable options:

SQLApi++

MySQL++

Not trying to come on like a salesman or anything and I have no affiliation with any of these but sometimes it never hurts to shop around and find something that works better for your needs.

Answer 3

error LNK2001: unresolved external symbol _get_driver_instance

That error message basically means that the linker cannot locate the function get_driver_instance anywhere, eg. it's not in any of the object files from your compilation units, not in a static .lib library or import library. This can also happen if the mangled names in the library doesn't match exactly with what the linker expects to find. eg. Library was built with different calling convention etc.

I would suggest that you take a look at the final command line being used from your project and update your post here for both compiling and linking. Second, make sure the mysql library you're linking against has that function. I believe there's a commandline tool in vs for dumping and viewing the contents of a static lib.

If you're linking against a dynamic dll version of mysql, make sure the import library contains the missing referenced symbol. Additionally, you can crack the dll open with a PE viewer and look under it's export tables to verify that that function actually exist and is visible.

Edit: According to this post, the function get_driver_instance should be in 'mysqlcppconn.lib' somewhere. Are you sure that file is being properly linked?

Answer 4

If you use static linking, you need to set CPPCONN_PUBLIC_FUNC= in Project / Properties / C++ / Preprocessor / Preprocessor Definitions

Answer 5

I read the article you mentioned. It has this line for static compilation : As said, you need to link both "mysqlcppconn-static.lib" and "libmysql.lib".

Since you don't mention this is you question ,have you tried this ?

Also , on a forum I read this (for eclips) "You must have this in source":

#include "mysql_driver.h" 
#include "mysql_connection.h"
using namespace sql::mysql; 

Anyway ,good luck !

Answer 6

I faced Same Error while using c++/Sql Connector. and after spending entire day I solved this problem by using 32 bit libmysql.dll , 32 bit libmysqlcppcon.lib and 32 bit libmysqlcppcon.dll ( Dynamic binding is used because driver instance creation is only available in dynamic library of libmysqlcppcon.lib)

I found very good link explaining everything along with the working code. I think it would help others if they stuck at the same issue.

http://r3dux.org/2010/11/how-to-use-mysql-connectorc-to-connect-to-a-mysql-database-in-windows/