DYNAMIC LINK LIBRARY VERSION
BACKGROUND OF THE INVENTION
(1) Related Application
This application is a continuation-in-part of Ser. No. 154,269, filed Nov. 18, 1993, now abandoned which has been assigned to the assignee of this application.
(2) Field of the Invention
The present invention relates to the field of computer systems and computer software applications. Specifically, the present invention relates to the field of computer program development and execution.
Some programs executed by computer systems are constructed using a particular set of development tools and are translated from a high level programming language to an executable format according to a particular process. For instance, in order to develop a program written in a high level language, such as the C language, a program is first entered into an editor using the C instruction format and the "C program" is then compiled by a compiler program. The compiler program transfers the C instructions into assembly instructions represented as assembly code (often called machine code). The resultant output from the compiler program is called the ".obj file" or object code.
There may be several different object files stored on a disk drive or in a computer's memory and each may represent a different section of the high level program. Therefore, a given C program may reference several object files. Such is well known in the prior art. As the high level program is compiled, object files that are referenced by the program do not have to be compiled again each time. This saves development time.
Several object files may be combined together into a library file or ".lib file." Often used and rarely changed subroutines are compiled into object files and then placed into an object code library file so that they do not have to be compiled each and every time the C program is compiled. This is done in an effort to reduce the compile time of the high level program. If a subroutine is not going to change from one version of the high level program to the next, there is essentially no need to recompile the subroutine for each version of the high level program and therefore the object code library provides the compiled result when needed. In effect, the predefined object code files are "canned" subroutines that have been previously written and compiled and are not expected to change readily.
A linker program is used to link the various object files together and to create a resultant executable file or ".exe file." Therefore, a high level program is compiled then combined with previously compiled files that are referenced by the high level program (if any) and the total is linked to together to create an executable version of the program or "application." The executable file is the file that will be executed by the computer system to perform the instructions that were originally developed in the high level language (i.e., of the C program). The executable file may be referred to as the "executable application."
Also included in the above procedure is a file called the header file or ".h file." The header file contains, among other things, variable definitions and procedure and function definitions that may be incorporated into the high level program by reference. This purpose of the header file is to provide a readily available method of incorporating often used deft
nitions into the high level program without requiring the high level program (i.e., the C program) to recite each definition individually. In other words, a group of variable definitions and or procedure or function definitions (that are 5 expected to used by many applications) may be given a common name, such as "<myfiles.h>." Then, where ever the high level program includes a statement, such as the one listed below:
# include <myfiles.h>,
the compiler will read the header file for the <myfiles.h> definitions and will incorporate these definitions and/or instructions into the high level program at that point. The result is that the definitions and/or instructions within the
15 <myfiles.h> group will be compiled by the compiler program as if they appeared in the high level program originally at the location where the include statement appears. Use of a header file in the above configuration is also well known in the prior art. In the manner as described above a header
20 file may be viewed as a development tool for the application. Developments have lead to the introduction of Dynamic Link Library files (DLL files or DLLs) which are files that contain executable program code that corresponds to particular subroutines and program sections. Similar to the
25 notion of providing "canned" object files, Dynamic Link Library files provide "canned" subroutines in executable code format that can be called by other applications to perform certain, known functions.
At run time, these subroutines can be directly called by
30 the executable application in order to perform various tasks. Therefore, the DLL must be resident in memory when the application is executed. In other words, at execution time, the resultant executable code that is produced by the linker program from the high level instructions will call certain
35 subroutines for execution that exist within the DLL file. This requires that the DLL be loaded into the computer system's memory (or available for loading) before the executable program is executed. Therefore, before an executable program (created by the high level language) is executed, the
40 DLL is loaded into the computer's memory.
However, as is often the case, the DLL file that is loaded into memory may or may not be completely compatible with the current executable application that calls subroutines located within the DLL file. This problem arises because the
45 DLL file called by the executable file can be updated and altered after the executable program is developed. Therefore, the DLL resident in memory may not be the DLL expected by the application file even though the subroutine names (of the DLL) are the same. Further, the executable
50 program can be altered and developed after the creation of the DLL file that is called by the executable program.
It is important that the DLL file accept and supply the exact data and control interface expected by the executable file or serious errors will develop in the execution of the
55 executable file. Therefore, it would be advantageous to provide a mechanism to insure that the data interfaces between a DLL file and an executable program are compatible. It is further advantageous to provide a system and method for insuring that the DLL resident in memory is that
60 DLL anticipated by the executable application. The present invention provides such capability.
It is further advantageous to be able to insure that a given subroutine within a DLL file and called by an executable file is the same subroutine that is expected by the executable file.
65 The present invention provides such advantageous functionality. It is further advantageous to be able to negotiate which version or revision level of a given subroutine within a DLL