In a *.cpp file, trying to use a third party lib:
#define DLL_IMPORT
#include <thirdParty.h>
// Third party header has code like:
// #ifdef DLL_IMPORT
// #define DLL_DECL __declspec(dllimport)
// fatal error C1001: An internal error has occurred in the compiler.
Alternative:
#define NO_DLL
#include <thirdParty.h>
// Third party header has code like:
// #elif defined(NO_DLL)
// #define DLL_DECL
// Compiles fine, but linker errors as can't find DLL functions
I can reproduce results by remove macros and #define all together and manually editing the third party files to have __declspec(dllimport) or not - so the preprocessor stuff above is just to show what's going on, it's not copy-paste.
Has anyone come across anything similar, or can hint at the cause? (which is created using CMake). Above is actual example of 2 line *.cpp that crashes so it's narrowed down to something in the #include.
The following also work fine:
Compile the examples provided by the third party (they provide a *.sln) that use dllimport/export so it doesn't appear to be the fault of the library
Compile the third party lib as part of the production project (so dllexport works fine)
I've trawled the project settings pages of the two projects to try and spot differences, but have come up blank. Of course, it's possible I'm missing something as those settings pages are not the easiest to navigate. I'll get access to VS2008 in a day or so, so can compare with that. The third party library is MySql++.
A compiler crash is definitely a bug in the compiler, so you're best off submitting an error report to the Microsoft Visual C++ team.
As for the error
#define DLL_DECL __declspec(dllimport)
is the wrong way to go about things. There should be some project setting you need to set, a pre-processing directive you can define instead if DLL_DECL, or simply including a different file.
Turns out it was because precompiled headers was turned on for the project trying to use the DLL.
Related
So I'm currently working on something that uses OpenCL. The OpenCL spec provides the users with a directive which must be included before the inclusion of the header (cl.h)
#define CL_TARGET_OPENCL_VERSION 110
Which basically defines the version they want to use. Suppose I'm making a library and I want my users to define this instead of me defining this inside my files. What I did was.
-----main.cpp---
#define CL_TARGET_OPENCL_VERSION 110
#include "library.h"
-------x---------
----library.h-----
#ifdef CL_TARGET_OPENCL_VERSION
#pragma message("def")
#endif
#ifndef CL_TARGET_OPENCL_VERSION
#pragma message("ndef")
#endif
.... include other headers.
--------x---------
And the compiler prints both def and ndef messages. And the OpenCL library also throws a warning that it's undefined. I thought that the library header would get substituted into main and it'd only print the def message. Is there anything I understood wrong?
I'm particularly confused as to where does the preprocessor start? If it starts from main.cpp and goes from top to down, then it surely has defined the macro. After that it sees the library inclusion, then it should only print the def message but it prints both.
This leds me to believe the preprocessor does scan the header file before including it in main? Dunno the reason why. Also I have assured that the library header isn't included elsewhere.
One interesting thing I noticed was, if i did this
-----helper.h---
#define CL_TARGET_OPENCL_VERSION 110
-------x---------
----library.h-----
#include helper.h
#ifdef CL_TARGET_OPENCL_VERSION
#pragma message("def")
#endif
#ifndef CL_TARGET_OPENCL_VERSION
#pragma message("ndef")
#endif
.... include other headers.
--------x---------
It prints the def message "twice". If anybody can explain all this I'd be grateful.
EDIT:- The files I'm compiling are main.cpp library.h and library.cpp
Library.cpp includes library.h from the start as usual. Maybe this other cpp is causing the problem?
In C/C++ programs, the compiler handles each .c and .cpp file separately.
The compilers build each source file (NOT the header files, only .c and .cpp files) independently from each other (this source files are called compilation unit).
Thus, when your main.cpp is built, the compiler finds the #define CL_TARGET_OPENCL_VERSION 110 you have added on top of the main.cpp file, emiting the defmessage.
But when the compiler builds the library.cpp file, it does not find the version define, so it emits the ndef message.
So, following this explanation, it is completely normal that in your last case, when you add the define to the .h file, the compiler emits the def message twice, once for the main.cpp file and once for the library.cpp file.
Now, the problem is where should you add the define, in order to have the program built consistently, with the same version for all the .cpp files.
Usually, all the IDEs have some configuration page where you can add global defines, for all the project, which are "inserted" into all the compilation units before everything else. So when the IDE calls the compiler, it passes the same defines to all the compilation units. You should add this kind of defines in this page.
In your IDE (I am using Code::Blocks, v 17.12), you can find this page in the menu: Project / Build Options
For each type (Debug or Release), you have to go to the tab Compiler Settings, and there to the sub tab #defines. There you can add global defines, which can be different if you are building in Debug or in Release mode (of course, if you set the same in both modes, they would be the same).
Once you have added your define here, please, remove it from the main.cpp, library.h and any other place where you may have added it, in order to avoid duplicities.
From the comments about portability:
You have several options:
Always use Code::Blocks: this would be the easiest way, since you can pass the Code::Blocks project along with the source files, and everything would be already setup.
Use cmake, which is a script build system, where you can set defines and so in the same way as using an IDE. cmake is much widely used than Code::Blocks, so maybe it is a better option.
Add a new options.h header file, where you set all the defines, and include it to all your .c/.cpp. This setup has the additional benefit that for different systems, changing only the options.h file the build can be completely different. This is a manually setup of what the IDE is doing. It has the advantage that does not rely on external tools, but the disadvantage that you have to remember to add it in all the new .cpp files added to the project.
My recommendation is go with cmake, just as the others have said.
Prefer using #ifndef XXXX_h #define XXXX_h #endif over #pragma once
If your #include search path is sufficiently complicated, the compiler may be unable to tell the difference between two headers with the same basename (e.g. a/foo.h and b/foo.h), so a #pragma once in one of them will suppress both. It may also be unable to tell that two different relative includes (e.g. #include "foo.h" and #include "../a/foo.h" refer to the same file, so #pragma once will fail to suppress a redundant include when it should have.
This also affects the compiler's ability to avoid rereading files with #ifndef guards, but that is just an optimization. With #ifndef guards, the compiler can safely read any file it isn't sure it has seen already; if it's wrong, it just has to do some extra work. As long as no two headers define the same guard macro, the code will compile as expected. And if two headers do define the same guard macro, the programmer can go in and change one of them.
#pragma once has no such safety net -- if the compiler is wrong about the identity of a header file, either way, the program will fail to compile. If you hit this bug, your only options are to stop using #pragma once, or to rename one of the headers. The names of headers are part of your API contract, so renaming is probably not an option.
(The short version of why this is problematic to use #pragma is that neither the Unix nor the Windows filesystem API offer any mechanism that guarantees to tell you whether two absolute pathnames refer to the same file.)
I've downloaded the latest copy from Latest Open EXR repo and compiled most everything without any problems. However, when I get to PyILMBase it fails.
There are two distinct issues with my attempts:
Error C2491 'PyImath::FixedArray::name': definition of dllimport function not allowed PyImath (...)\src\pyilmbase-2.2.1\PyImath\PyImath.cpp 41
and an import to unistd.h that kind of gets addressed Here
my question being, has anybody successfully compiled this for windows? It seems odd that I can't find any specific info about that compiling error. Am I missing something in the way that C++ works?
This project makes extensive use of whatever it is that causes the error C2491, so going in and changing it would be a little complicated
IlmBase is compiled as a shared library. A shared library must provide their function declarations in order your program can find them.
It's perform by declaring them as dllimport or dllexport depending on the situation.
__declspec(dllimport): imports the implementation from a DLL so your application can use it.
__declspec(dllexport): tells the linker that you want this object to be made available for other DLL's to import. It is used when creating a DLL that others can link to.
These keywords are generally handled by a single macro. In your case PYIMATH_EXPORT.
These lines are from PyImathTask.h
#if defined(PYIMATH_EXPORTS) // create library
#define PYIMATH_EXPORT __declspec(dllexport)
#else // use library
#define PYIMATH_EXPORT __declspec(dllimport)
#endif
So, because you want to make these functions available from your application, you must add PYIMATH_EXPORTS as a preprocessor definition.
Actually, PyIMath's properties mispells it - they've write it as PyImath_EXPORTS - ...
To fix that, in vs2015, go to the PyImath's properties > Configuration Properties > C/C++ > Preprocessor > Replace PyImath_EXPORTS by PYIMATH_EXPORTS.
It's probably the same thing for PyIex...
I have a bunch of Dll's in my project, using VStudio 9.0 compiler, pre-compiled headers are used for all my Dll's. The dll's loading process is done by implicit caller (.dll, .lib and header must be supplied).
I typically create a different macro definition file per dll, for instance if my current Dll is called MYMacroDll I add a file _MyMacroDll.h which contains:
#ifndef _MYMACRODLL_H_
#define _MYMACRODLL_H_
#ifdef _WIN32
#ifdef MYMACRODLL_EXPORTS
#define MYMACRODLL_API __declspec(dllexport)
#else
#define MYMACRODLL_API __declspec(dllimport)
#endif
#define MYMACRODLL_CALL __cdecl
#else
#define MYMACRODLL_API
#define MYMACRODLL_CALL
#endif
#endif
I know the code can be simplified but I keep the last defines for portability, at least, that's what I understood...
The pre-compiled header file pch.h, will always include the macro definition file _MyMacroDll.h, this makes things easier to me, 'cause later I can decide whether a new class or function will be interfaced or not. This so far works correct.
The confusion comes from using the dll interfaces in another dll; let's suppose a second dll ImageLoaderDll. This one uses instances or references of one (or several) of the interfaced classes/functions in _MyMacroDll. At first glance I guessed there was no need of including the _MyMacroDll.h, but when compiling the ImageLoaderDll it complains with
error C2470: '_AnInterfaceClassFromMyMacro' : looks like a function definition, but there is no parameter list; skipping apparent body
Then I have to include the _MyMacroDll.h in the pre-compiler header file of the other Dll, my project is becoming really messy and I find more and more useless dependencies.
What am doing wrong? Is there another way of setting up the macro definitions so I can avoid adding it to the client Dll's? Am not an expert regarding software design, but in this situation the more decoupled the better.
Hope my explanation was good enough.
If you are using the DLL interface from MyMacroDll in ImageLoaderDll, then you do have a dependency. ImageLoaderDll should include _MyMacroDll.h, otherwise you can't call its functions correctly. It's exactly the same as including <string.h> when you want to call strlen.
let's say I am distributing a library as binary. It is shipped in two versions, debug and release. Debug and release are incompatible with each other, so if e.g. the user builds a release executable, he/she must link with release library.
If there is a mismatch between library and executable versions, currently there will be subtle errors that are really hard to figure out. I would instead like to show a really clear error message that informs there is a mismatch, preferably at link time.
What would be a good way to achieve this?
I'm going to assume that you are using a static library and by binary you mean a .lib that will be linked at compile time (as opposed to a dll or the like that might be mismatched at run-time).
Seems to me the easiest way is to have this sort of a construct in your .h file
#ifdef _RELEASE //or whatever your compiler uses
#define InitialiseLibrary InitialiseLibraryRelease
#else
#define InitialiseLibrary InitialiseLibraryDebug
#endif
Similarly in the cpp file of the library:
#ifdef _RELEASE //or whatever your compiler uses
void InitialiseLibraryRelease()
{
CommonInitialise();
}
#else
void InitialiseLibraryDebug()
{
CommonInitialise();
}
#endif
Now in the main exe which is using the library:
InitialiseLibrary();
If the release-ness of the library and exe don;t match then the linker will report not matching one or other InitialiseLibrary... function.
A different option is to ensure that the release and debug libraries compile to differently named files and then get the link to work using #pragma in the .h file (as opposed to explicitly including the library in a project).
Using the #ifdef as above you can select at compile time which library to link by choosing which #pragma is used. This second technique doesn't exactly address your question (as it doesn't STOP the link happening if the programmer tries to force it) but it is a normal way of dealing with difficulties of this sort (and has advantages in complex build environments)
Could also checksum the binaries/libraries in your install script. Not a C answer, though.
Use #error directive, that will abort the compilation:
#ifndef RELEASE_VERSION
#error Release version required
#endif
I've managed to get input hooks working, but now I'm kinda lost with putting them into a library.
I have a simple header with INPUTHOOK_EXPORTS defined in the IDE, so the dll exports (Visual Studio).
#pragma once
#ifdef INPUTHOOK_EXPORTS
#define INPUTHOOK_API __declspec(dllexport)
#else
#define INPUTHOOK_API __declspec(dllimport)
#endif
INPUTHOOK_API void InstallInputHook();
INPUTHOOK_API void RemoveInputHook();
and of course:
The cpp file
The thing is, when I try to compile this library, I get two unresolved externals, one for SetWindowsHookEx and for UnhookWindowsHookEx respectively. Why these two functions are not available, while others are and without any problem? As far as I see, I do have the includes right.
Thank you
SetWindowsHookEx is a macro that should turn into SetWindowsHookExA' for ascii orSetWindowsHookExWfor wchar. Similary forUnhookWindowsHookEx` .
The error reported should be specific to which function is missing - A or W - which seems to indicate for some reason the macro is not in place.
You seem to be missing winuser.h in the cpp, however this or an equivalent may be in the pre-compiled stdafx.h header.
You need to include user32.lib while building (linking) your library (normally in the default included libs).
From MSDN topic LowLevelKeyboardProc:
This hook is called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop.