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Warning C4251 during DLL compilition due to missing IMGUI_API #345

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ZahlGraf opened this issue Sep 20, 2015 · 4 comments
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Warning C4251 during DLL compilition due to missing IMGUI_API #345

ZahlGraf opened this issue Sep 20, 2015 · 4 comments
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@ZahlGraf
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Hi

When compiling IMGUI as DLL I get several warnings C4251 like:

warning C4251  class "ImVector<ImDrawIdx>" needs to have dll-interface to be used by clients of  struct "ImGuiTextEditState"

The background of this warning is, that the struct ImGuiTextEditState is exported with IMGUI_API and it uses the ImVector class that is not exported with IMGUI_API. However when a class is exported and uses other classes/structs as member or base, the other classes and structs must be exported too, otherwise link-errors could occur when using the struct ImGuiTextEditState in the application.

The warning appears for the following classes/structs:
ImVec2 (imgui.h)
ImVec4 (imgui.h)
ImVector (imgui.h)
ImGuiDrawContext (imgui_internal.h)

I had a deeper look at these classes/structs and it seems that all of those are pure inline classes. This means there is not a single method that is not inline. In this case a link-error would not occur, since all necessary information for linking is available.
However my Visual Studio 2015 compiler seems just to check if all classes are exported correctly, independent of if this is really necessary for linking.
I added IMGUI_API to those classes/structs and was able to compile a DLL without any other warnings.

Best regards,
André

@ZahlGraf ZahlGraf changed the title Warning C4251 durint DLL compilition due to missing IMGUI_API Warning C4251 during DLL compilition due to missing IMGUI_API Sep 20, 2015
@ocornut
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ocornut commented Sep 21, 2015

Thanks, will look into it. I would like to make sure that those DLL interfaces don't have a performance effect on both sides of the fence.

@ZahlGraf
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Thanks for looking into it.

@ocornut
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ocornut commented Sep 21, 2015

I looked at this, one problem is that specifying IMGUI_API spreading to template enforce instantiating template specialization within the DLL and application seems to want to link to it there. It's too risky - can't afford letting those inline functions be not-inlined in a DLL context.

So I have silenced the warning (NB: there are other legit official reasons to silence this warning).

It won't be a problem as long as you use the same version of imgui on both side .lib/.dll anyway (even so, those classes layout are unlikely to change).

@ocornut ocornut closed this as completed Sep 21, 2015
@ZahlGraf
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Thanks a lot for the fast fix.

idbrii added a commit to idbrii/cpp-imgui that referenced this issue Mar 24, 2025
Includes my merged PRs and everything in my dev branch. Haven't tested
with it yet.

Changelog:
Test case for clip rect
HACK: more recent Windows SDK and VS2017; disable graph
Set size to amount of space required
Merge pull request ocornut#349 from maksw2/master
Merge pull request ocornut#347 from mgerhardy/341
Merge pull request ocornut#348 from mgerhardy/fixed-warning
Merge pull request ocornut#346 from mgerhardy/280
Merge pull request ocornut#345 from mgerhardy/322
Merge pull request ocornut#344 from rherilier/fix-gcc-warnings
Merge pull request ocornut#336 from rherilier/add-isusingviewmanipulate
Merge pull request ocornut#335 from RedSkittleFox/alternative_window
Merge pull request ocornut#334 from ocornut/fix-beginchildframe
dear imgui update and small fixes
Merge pull request ocornut#316 from Batres3/2DSupport
Merge pull request ocornut#326 from Sayama3/use-push-pop-id
Merge pull request ocornut#328 from georgeto/master
Merge pull request ocornut#330 from maritim/master
Merge pull request ocornut#331 from GiovanyH/patch-1
Merge pull request ocornut#318 from dougbinks/imgui_math_operators
Merge pull request ocornut#312 from kimidaisuki22/master
div 0 fixed
Merge pull request ocornut#301 from ZingBallyhoo/using-any
Merge pull request ocornut#300 from Clog41200/Configurable-limits
Merge pull request ocornut#298 from xDUDSSx/fix/rotation_circles
Merge pull request ocornut#297 from xDUDSSx/fix/vertical-aspect-scaling
Merge pull request ocornut#289 from ComputationalBiomechanicsLab/fix_isusing-ignores-setid
Merge pull request ocornut#291 from ocornut/fix_math_operators_include
Merge pull request ocornut#282 from MohitSethi99/master
Merge pull request ocornut#276 from pthom/virtual_destructors
Merge pull request ocornut#271 from idbrii/clip-parent
Merge pull request ocornut#270 from idbrii/btn-behaviour
Merge pull request ocornut#265 from mgerhardy/pr/fix-minor-formatting
Merge pull request ocornut#264 from mgerhardy/pr/div0
Merge pull request ocornut#269 from peter1745/hatched-line-thickness-enhancement
Merge pull request ocornut#259 from miyanyan/master
Merge branch 'master' of https://github.com/CedricGuillemet/ImGuizmo
update dear imgui
Merge pull request ocornut#256 from Aidiakapi/patch-1
Merge pull request ocornut#252 from aaronkirkham/master
Merge pull request ocornut#249 from rokups/rk/mouse-capture
Merge pull request ocornut#246 from mgerhardy/pr/viewmanipulate
removed commented code
fix click view cube
Merge pull request ocornut#231 from mgerhardy/master
Merge pull request ocornut#230 from mgerhardy/master
Merge pull request ocornut#228 from longod/master
Merge pull request ocornut#227 from madeso/master
AddBezierCubic
Merge pull request ocornut#226 from sherief/master
revert culling test commit
Merge pull request ocornut#203 from rokups/rk/misc-fixes
Merge pull request ocornut#212 from zhaijialong/fix-behind-camera-cull
Merge pull request ocornut#209 from VictorFouquet/fix_normalize
scale is always local
Merge pull request ocornut#202 from pezy/master
imguizmo namespace
Merge pull request ocornut#194 from JonathanHiggs/vcpkg-example
1.84 WIP
Merge pull request ocornut#197 from idbrii/seq-btn-color
Merge pull request ocornut#196 from idbrii/seq-big-handles
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