https://github.com/synergex/sampledll

This code sample demonstrates three different use cases for returning values from a DLL routine: 1. Returning a simple integer value 2. Returning a pointer to a data structure 3. Returning a pointer to a pointer to a data structure
https://github.com/synergex/sampledll

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This code sample demonstrates three different use cases for returning values from a DLL routine: 1. Returning a simple integer value 2. Returning a pointer to a data structure 3. Returning a pointer to a pointer to a data structure

• Host: GitHub
• URL: https://github.com/synergex/sampledll
• Owner: Synergex
• License: other
• Created: 2021-12-16T17:16:01.000Z (over 4 years ago)
• Default Branch: main
• Last Pushed: 2022-07-25T20:12:12.000Z (almost 4 years ago)
• Last Synced: 2025-11-09T12:02:27.412Z (8 months ago)
• Language: C
• Homepage:
• Size: 18.6 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md

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README

          
# SampleDLL


**Created Date:** 11/17/2009


**Last Updated:** 11/17/2009


**Description:** This code sample demonstrates three different use cases for returning values from a DLL routine: 1. Returning a simple integer value 2. Returning a pointer to a data structure 3. Returning a pointer to a pointer to a data structure


**Platforms:** Windows


**Products:** Synergy DBL; DLL API


**Minimum Version:** 9.1.5


**Author:** Chip Camden



**Additional Information:**

File included:

sample.dbl Example Synergy/DE program that calls the DLL routines

and processes the returned values.

SampleDLL.sln A Microsoft Visual Studio solution for building the DLL

SampleDLL/*.* Source files for the DLL (see especially SampleDll.(cpp,h))

Release/SampleDLL.dll A 32-bit version of the DLL

x64/Release/SampleDLL.dll A 64-bit version of the DLL

NOTES ON SPECIFIC FUNCTIONS

fnSampleDLL

This function merely returns an integer value.

fnSampleDLLptr

This function returns a pointer to a data structure SAMPLESTRUCT

that is defined in SampleDLL.h and duplicated as sampleStruct in

sample.dll. Note that the C++ routine returns the address of

one of these structures, which MUST BE PERSISTENT. In this case,

we use a static. If the structure were an auto variable, then it

would be released upon return from this routine, which could cause

unpredictable failures.

In the Synergy/DE code, the pointer is dereferenced by registering

a memory handle to the address, and mapping it to the structure

that we have defined to match the structure from the DLL.

fnSampleDLLptrptr

This function returns a pointer to a pointer to the same data

structure. In this case, we must first dereference the returned

pointer to obtain a pointer to the structure. The same rules

apply with regard to the persistence of the items referenced --

in this case, both the structure and the pointer to it must

persist beyond the return from the routine, so statics are used

for both.

On the Synergy/DE side, we register a handle to the returned address,

then treat that handle as referencing an integer value of the size

D_ADDRSIZE (the size of a pointer). This will work for both 32-bit

and 64-bit platforms, because we use D_ADDRSIZE. Then we can take

that value and treat it as a pointer, the same as if it had been

returned by fnSampleDLLptr.

The same principle can be applied to pointers that are returned as

members of a data structure, or a pointer to an array of pointers.

In the latter case, simply increment the pointer to the array by

D_ADDRSIZE to access the next pointer in the array.