Writing a data-conversion exit for IBM MQ for Windows

Information about steps to consider when writing data-conversion exit programs for IBM MQ for Windows.

Follow these steps:

Name your message format. The name must fit in the Format field of the MQMD. The Format name must not have leading blanks. Trailing blanks are ignored. The object's name must have no more than eight non-blank characters, because the Format is only eight characters long.
A .DEF file called amqsvfcn.def is also supplied in the samples directory, MQ_INSTALLATION_PATH\Tools\C\Samples. MQ_INSTALLATION_PATH is the directory where IBM MQ is installed. Take a copy of this file and rename it, for example, to MYFORMAT.DEF. Make sure that the name of the DLL being created and the name specified in MYFORMAT.DEF are the same. Overwrite the name FORMAT1 in MYFORMAT.DEF with the new format name.

Remember to use this name each time that you send a message.
Create a structure to represent your message. See Valid syntax for an example.
Run this structure through the crtmqcvx command to create a code fragment for the data-conversion exit.
The functions generated by the CRTMQCVX command use macros that are written assuming that all structures are packed; amend them if this is not the case.
Copy the supplied skeleton source file, amqsvfc0.c, renaming it to the name of our message format that you set in step 1.
amqsvfc0.c is in MQ_INSTALLATION_PATH\Tools\C\Samples where MQ_INSTALLATION_PATH is the directory where IBM MQ is installed. (The default installation directory is C:\Program Files\IBM\MQ.)

The skeleton includes a sample header file amqsvmha.h in the MQ_INSTALLATION_PATH\Tools\C\include directory. Make sure that your include path points to this directory to pick up this file.

The amqsvmha.h file contains macros that are used by the code generated by the CRTMQCVX command. If the structure to be converted contains character data, these macros call MQXCNVC.
Find the following comment boxes in the source file and insert code as described:
1. Toward the end of the source file, a comment box starts with:
```
/* Insert the functions produced by the data-conversion exit */
```
  Here, insert the code fragment generated in step 3.
2. Near the middle of the source file, a comment box starts with:
```
/* Insert calls to the code fragments to convert the format's */
```
  This is followed by a commented-out call to the function ConverttagSTRUCT.
  Change the name of the function to the name of the function that you added in step 5.a. Remove the comment characters to activate the function. If there are several functions, create calls for each of them.
3. Near the beginning of the source file, a comment box starts with:
```
/* Insert the function prototypes for the functions produced by */
```
  Here, insert the function prototype statements for the functions added in step 3.
Create the following command file:
```
cl -I  MQ_INSTALLATION_PATH\Tools\C\Include -Tp   \
MYFORMAT.C



MYFORMAT.DEF
```
where MQ_INSTALLATION_PATH is the directory where IBM MQ is installed.
Issue the command file to compile your exit as a DLL file.
Place the output in the exit subdirectory below the IBM MQ data directory. The default directory for installing your exits on 32 bit systems is MQ_DATA_PATH\Exits and for 64 bit systems is MQ_DATA_PATH\Exits64 The path used to look for the data-conversion exits is given in the registry. The registry folder is:
```
HKEY_LOCAL_MACHINE\SOFTWARE\IBM\WebSphere MQ\Installation\MQ_INSTALLATION_NAME\Configuration\ClientExitPath\
```
and the registry key is: ExitsDefaultPath. This path can be set for each queue manager and the exit is only looked for in that path or paths.

Note:

If CRTMQCVX uses packed structures, all IBM MQ applications must be compiled in this way.
Data-conversion exit programs must be reentrant.
MQXCNVC is the only MQI call that can be issued from a data-conversion exit.

Parent topic: Writing data-conversion exits