DLL Programmer's Guide for TNS/R Systems

Essential DLL Facility Controls

DLL Programmer’s Guide for TNS/R Systems—522203-002

2-15

Some Examples Using Re-Exportation

Replacing an Existing Symbol Definition

In a working DLL you can make a new version of an existing symbol having new

function without recompiling that DLL, so that all client loadfiles that use this symbol

will invoke the new function without being altered. Starting from the situation in

Figure 2-1 on page 2-14, Figure 2-3 on page 2-15 illustrates how a new DLL can

combine with an existing DLL to replace the old function. The steps to accomplish this

are:

1. Relink DLL D and rename it DLL Y.

2. In a new DLL D, construct the new procedure to provide the new function and

name its entry point Gamma, the same name as the replaced function in the old

DLL D. Put Y in D’s libList and designate Y re-exported, so users can still access

the old symbols Alpha and Beta from D.

Figure 2-2. Splitting a DLL Into Two Parts

Figure 2-3. the New Symbol, Gamma, With New Function (Shaded), Replaces

the Old Gamma.

DLL A

Alpha

Beta

Gamma

DLL D

(new)

Gamma

VST022.vsd

DLL Y

(new)

Alpha

Beta

DLL A

Alpha

Beta

Gamma

DLL D

(new)

Gamma

VST023.vsd

DLL Y

(old D)

Alpha

Beta

Gamma