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HP OpenVMS Systemsask the wizard |
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The Question is: We have our own application written in C that uses an API provided by a 3rd party as a library (lets call it l3p.olb). We have other 3rd party applications that also use the API in l3p.olb We want to add to the functionality of one routine in l3p.olb (lets call it api_1) so that it does some logging and then carries on as before. We want this enhanced functionality to be apparent in all applications using l3p.olb The proposal is to have our own function of the same name (api_1) in a library that all applications link to that does the extra work and then calls the original api_1 in l3p.olb 1) Is this proposal workable i.e. how could it be done without the new api_1 function re-calling itself ? 2) How would you overcome possible linker symbol resolution conflicts. Many Thanks, Credit Suisse First Boston, Hr. Andrew Bartle, FTIS 1 / Front Office IT Postfach 900 8070 Z|rich Tel. +41 (0)1 332 3355 e-mail andrew.bartle@csfb.com The Answer is : Use CC/PREFIX or a preprocessor define in a common header file when you compile your applications, specifying a prefix or alternate name for the particular target routine. The routine that calls the "real" version of the routine is compiled without the prefix or define, obviously. As an alternative, you could extract the object module from the library, patch the symbol name, and replace it. With the inclusion of a module you created, you could then redirect the access to the "new" name for the "real" routine. This whole interception process is far easier when the library is built as a shareable image -- please see the available cookbook for details on creating a shareable image. Through the use of a "stub" shareable image, any and all routines can be intercepted or otherwise tailored as required.
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