Customizing DLL loading

To dynamically load a SOM class, the SOMClassMgrObject calls the function pointed to by the global variable SOMLoadModule to load the DLL containing the class. The reason for making public the SOMLoadModule function (and the following SOMDeleteModule function) is to reveal the boundary where SOM touches the operating system. Explicit invocation of these functions is never required. However, they are provided to allow class implementors to insert their own code between the operating system and SOM, if desired. The SOMLoadModule function has the following signature:

long (*SOMLoadModule)

( string className,
string fileName,

string functionName,

long majorVersion,

long minorVersion,

somToken *modHandle);

This function is responsible for loading the DLL containing the SOM class className and returning either the value zero (for success) or a nonzero system-specific error code. The output argument modHandle is used to return a token that can subsequently be used by the DLL-un loading routine (described below) to unload the DLL. The default DLL-loading routine returns the DLL's module handle in this argument. The remaining arguments are used as follows:

Argument

Usage
fileName
The file name of the DLL to be loaded, which can be either a simple name or a full path name.
functionName
The name of the routine to be called after the DLL is successfully loaded by the SOMClassMgrObject. This routine is responsible for creating the class objects for the class(es) contained in the DLL. Typically, this argument has the value "SOMInitModule", which is obtained from the function SOMClassInitFuncName described above. If no SOMInitModule entry exists in the DLL, the default DLL-loading routine looks in the DLL for a procedure with the name <className>NewClass instead. If neither entry point can be found, the default DLL-loading routine fails.
majorVersion
The major version number to be passed to the class initialization function in the DLL (specified by the functionName argument).
minorVersion
The minor version number to be passed to the class initialization function in the DLL (specified by the FunctionName argument).

An application program can replace the default DLL-loading routine by assigning the entry point address of the new DLL-loading function (such as MyLoadModule) to the global variable SOMLoadModule, as follows:

#include <som.h>/* Define a replacement routine: */
long myLoadModule (string className, string fileName,
                   string functionName, long majorVersion,
                   long minorVersion, somToken *modHandle)
{
     (Customized code goes here)
}
...
SOMLoadModule = MyLoadModule;

---

[Back: Customizing class initialization]
[Next: Customizing DLL unloading]