MySql VCL Connector

[Prattaratt]

Does anyone out there have knowledge of a FREE VCL component library that would facilitate direct connections to a MySql Backend over the internet? I have tried ODBC connections, and this works fine for most of our offices, but we have a few that have extremely slow connections, and the connection does not get made (think it may be timing out, as these offices are on Hughes net). I have downloaded MySQL's CPP connector libray, but still have not been able to get it compiled yet. Any suggestions would be welcomed

 

[smays]

I believe there are some VCL components download-able from SourceForge.net I haven't tried them myself, so I cannot make any comment one way or the other.

I have not had success making the CPP connector from MySQL work, HOWEVER, I have gotten the C API to work (compile and actually transfer data back and forth from and to the server). There are a number of things you have to do, but the API does work with BCB. Several of the header files associated with the C API installation have to be 'amended' and there is one whole header file missing with the installation. Once you handle that, you can use the C API. The C API does use the "libmysql.dll" 'delivered' with practically everything downloaded from MySQL.

If you are interested, I can try my best to 'compile' my notes this evening as the work was done with my home PC.

You were specific about a "FREE VCL component" - I got that. That said, there are some very good components available for purchase.

Steve.

 

[radio9]

Hello Steve (smays),

While I'm not directly interested in the subject of the original post, I would be VERY interested in learning more about how you got the MySQL C API (not the C++ API) working from BCB.

If your kind offer to compile your notes on what tweaks you made to the MySQL C header files to make them BCB friendly is still on the table, I would very much appreciate it.

FYI -- Like you, I actually have achieved connectivity and basic queries with MySQL via the C API from Borland C++ Builder 6.0, but did this by excluding some of the required-or-recommended header files, specifically my_global.h and my_sys.h. Including mysql.h works fine. My concern with the exclusions is that some MACROS are not defined (not noticing a problem so far, but...) and apparently one of those header files is for Windows/Linus compatibility (ultimately this code will be compiled on Linux as well, and I'm concerned about potential data-type compatibility).

Also, I couldn't link with mysqlclient.lib as documented, but instead ran "implib libmysql_borland.lib libmysql.dll" and linked with the resulting .lib file instead (found this solution on the web and to my pleasant surprise, it seems to have worked -- unfortunately, I came across no solution to the header file problems).

I hope you are able to take the time to post your notes -- if so, THANK YOU VERY MUCH in advance.

Cheers,
-Brian

 

[smays]

Although my "kind offer" is still on the table, basically I did everything you said and got the same results, so I really have little to show.

Sorry.

Steve.

 

[radio9]

Hey Steve,

although I'm saddened by its content, I quite appreciate your reply .
Let's please keep each other posted here with any progress on this problem of compiling the C header files from the MySQL C API from Borland C++ Builder (BCB) (I'm spelling it out again here for the search engines).

Cheers and thanks!
-Brian

 

[radio9]

Here is a link to an article entitled "include MYSQL C API into Borland C++ Builder (BCB) Application" that I just came across:

http://libmysql.blogspot.com/

Note that I have not attempted the header file modification described there, as I still have not run into problems doing what I described above, and of course prefer to not have to re-modify the MySQL headers every time we upgrade to a newer MySQL C API version. But I recognize that I still may have to go that route if any hiccups occur with my current technique.

Cheers,
-Brian

 

[smays]

Thanks for the link, Brian. I am like you, I would hate to have to update the header file(s) every time I upgraded the C API. The trick is to convince MySQL to correct the header file(s) that ship with the C API product. I know the header files can be fixed to work with BCB without a lot of work, because I can download the SQLite amalgamation today, include it in a program, and compile/use it without any problem.

Steve.

 

[radio9]

Hey Steve,

another BCB requirement: it seems necessary to include the mysql.h file with QUAD WORD (8 byte) data alignment active. Since my BCB project settings are set to default to BYTE (1 byte) alignment, I used the following #pragma wrappers around the include:

#pragma pack(push, 8)
#include <mysql.h>
#pragma pack(pop)

This requirement only became apparent when I tried to bind 2 or more parameters to a Prepared Statement (via mysql_stmt_bind_param(...)). The above fixed the memory access exceptions that were triggered by the MySQL layer code.

Now if you have any pointers to a working thread-safe connection pool for this API, I'd appreciate any info! Haven't tried it myself yet, but googling has so far only turned up articles of concern regarding using a connection handle created in one thread by another thread.

Cheers again,
-Brian

 

[radio9]

For posterity, here's another requirement to get the application-side structure instances the same size as those expected in the MySQL dll: enums must be the size of ints. This was not the default setting in my BCB project, nor did I want to make it so, so here is how I did it in my source .c file:

#pragma option push -b	// Ensure 4-byte enums for Borland C
#pragma pack(push, 8)	// 8-byte data alignment for Borland C
#include <mysql.h>
#pragma pack(pop)
#pragma option pop

This requirement was NOT immediately obvious as all db functionality seemed to be working. I became suspicious of a problem when I tried to read a value from a "MYSQL" connection instance -- it wasn't what I expected. Further debug tests showed that mysql_init(MYSQL *conn) was zeroing out 968 bytes at conn, overshooting my pre-allocated buffer of only 960 bytes for an 8 byte buffer overrun.
The above #pragma makes my app-side MYSQL structure 968 bytes, the same size as the Microsoft-compiled MySQL C API DLL.

Hope this helps someone one day.
Cheers,
-Brian