I have dll project that includes additionally A.h header file. A.cpp includes A.h and B.cpp that has o header. If I do add B.cpp to visual c++ project compiler reports many errors :
Error 9 error LNK2005: "wchar_t * __stdcall aaa(int)" (?aaa##YGPA_WH#Z) already defined in A.obj C:\P\B.obj pr1
There are no problems and project compiles fine in case if I leave B.cpp in project directory, but not add it to project.
That is the problem with adding B.cpp file?
I thought that extensions has no influence and might be whatever you want. Correct me if I'm wrong, but I think I can rename B.h to B.fss , define this in source and compiler should compile
Your b.cpp will be automatically compiled if you include it in the project; and as you are including contents of the same file elsewhere as well, the code in it will be compiled again, resulting in duplicate definition errors
Basically if you include something that has definitions instead of declarations in one .cpp file and also add it to the project of course you will get multiple definition errors - move the definitions for the stuff in B.cpp to B.h and include that in A.cpp. The issue is not file extensions, the issue is that you need to understand that multiple definitions of the same thing will lead to such errors.
#include is for header files, not other .cpp files.
Remove #include "B.cpp" from A.cpp, and things will start behaving properly.
Or rename B.cpp to B.h if you intend to include it.
Related
I have unit a.cpp that is used in several projects in subdirectory libA. Some of project are using precompiled headers, while others -not. In this case projects that use precompiled header must have line:
#include <stdafx.h>
and projects that are not using PCH must have line:
#include "..\stdafx.h"
Wise verse is not working.
Why project sees stdafx.h file in different way when project uses PCH or not?
UPD.
When I replace line #include <stdafx.h> with #include "..\stdafx.h" in project that uses precompiled header i have error
Error 19 error C1010: unexpected end of file while looking for precompiled header. Did you forget to add '#include "stdafx.h"' to your source?
Directory structure is the same in both projects.
There is no (or there should not be any) difference between <stdafx.h> and "stdafx.h". The only significant difference is that one project "sees" the file in current folder, and the other project sees it in parent folder. This difference is controlled by compiler option Additional Include Directories. One project has libA in it, and the other does not have it.
I am porting an application from Solaris to Linux
The object files which are linked do not have a main() defined. But compilation and linking is done properly in Solaris and executable is generated. In Linux I get this error
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
My problem is, I cannot include new .c/.o files since its a huge application and has been running for years. How can I get rid of this error?
Code extractes of makefile:
RPCAPPN = api
LINK = cc
$(RPCAPPN)_server: $(RPCAPIOBJ)
$(LINK) -g $(RPCAPIOBJ) -o $(RPCAPPN)_server $(IDALIBS) $(LIBS) $(ORALIBS) $(COMMONLIB) $(LIBAPI) $(CCLIB) $(THREADLIB) $(DBSERVERLIB) $(ENCLIB)
Try adding -nostartfiles to your linker options, i.e.
$(LINK) -nostartfiles -g ...
From the gcc documentation:
-nostartfiles
Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib or -nodefaultlibs is used.
This causes crt1.o not to be linked (it's normally linked by default) - normally only used when you implement your own _start code.
-shared link option must be used when you compile a .so
The issue for me was, I by mistake put int main() in a namespace. Make sure don't do that otherwise you will get this annoying link error.
Hope this helps anyone :)
I had similar result when trying to build a new test project with boost, and it turned out that I was missing one declaration :
#define BOOST_TEST_MODULE <yourtestName>
I had this same problem when creating my c project, and I forgot to save my main.c file, so there was no main function.
I had a similar result when compiling a Fortran program that had C++ components linked in. In my case, CMake failed to detect that Fortran should be used for the final linking. The messages returned by make then ended with
[100%] Linking CXX executable myprogram
/lib/../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
make[3]: *** [myprogram] Error 1
make[2]: *** [CMakeFiles/myprogram.dir/all] Error 2
make[1]: *** [CMakeFiles/myprogram.dir/rule] Error 2
make: *** [myprogram] Error 2
The solution was to add
set_target_properties(myprogram PROPERTIES LINKER_LANGUAGE Fortran)
to the CMakeLists.txt, so that make prints out:
[100%] Linking Fortran executable myprogram
[100%] Built target myprogram
I had the same issue with a large CMake project, after I moved some functions from one code file to another. I deleted the build folder, recreated it and rebuilt. Then it worked.
Generally, with suddenly appearing linker errors, try completely deleting your build folder and rebuilding first. That can save you the headaches from trying to hunt down an error that actually simply shouldn't be there: There might be CMake cache variables floating around that have the wrong values, or something was renamed and not deleted, ...
I had the same issue as to OP but on on FreeBSD 13.1.
What solved the issue was simply adding:
int main()
{
}
Since the .cpp file was only an object file containing definitions and declarations using:
extern "C"
{
<all definitions and declarations code goes here>
}
Every time I tried compiling this, the compiler kept throwing the same error as to OP.
So all I did was add an empty main() function all the way at the bottom and code compiled with no errors.
I have a CMake module to locate FreeGLUT:
FIND_PATH(FREEGLUT_INCLUDE_DIR NAMES GL/freeglut.h)
FIND_LIBRARY(FREEGLUT_LIBRARY NAMES freeglut freeglut_static)
SET(FREEGLUT_LIBRARIES ${FREEGLUT_LIBRARY})
SET(FREEGLUT_INCLUDE_DIRS ${FREEGLUT_INCLUDE_DIR})
INCLUDE(FindPackageHandleStandardArgs)
FIND_PACKAGE_HANDLE_STANDARD_ARGS(FreeGLUT DEFAULT_MSG FREEGLUT_LIBRARY FREEGLUT_INCLUDE_DIR)
MARK_AS_ADVANCED(FREEGLUT_INCLUDE_DIR FREEGLUT_LIBRARY)
It works fine and locates freeglut_static.lib when I generate NMake Makefiles on Windows. I'm attempting to statically link FreeGLUT into my DLL:
FIND_PACKAGE(FreeGLUT REQUIRED)
ADD_LIBRARY(vti SHARED ${VTI_SOURCES})
ADD_DEFINITIONS("-DBUILD_VTI=1 -DFREEGLUT_STATIC=1")
INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/include ${FREEGLUT_INCLUDE_DIRS})
TARGET_LINK_LIBRARIES(vti ${FREEGLUT_LIBRARIES})
My source code builds correctly, but when it gets to the linking stage, VC++ fails with:
LINK : fatal error LNK1104: cannot open file 'freeglut.lib'
Which is strange since freeglut.lib isn't mentioned anywhere that I can see in the generated NMake makefiles. It should be trying to link with freeglut_static.lib, which CMake locates and sets in FREEGLUT_LIBRARIES.
What might be causing this?
This is caused with pragma directives in FreeGLUT code (see freeglut_std.h). Using FREEGLUT_STATIC should really fix that for you, but I think you should pass it to CMake without quotes: ADD_DEFINITIONS(-DBUILD_VTI -DFREEGLUT_STATIC)
I'm trying to compile a program which uses the alglib function pearsoncorr2.
Unfortunately I always get compilation errors like the following:
undefined reference to `alglib::real_1d_array::real_1d_array()'
I know that I have to compile all the dependencies of the alglib unit which contains the function I want to use. In my case it's statistics.h.
I'm including all the necessary files (ap.h, statistics.h, alglibinternal.h, alglibmisc.h, linalg.h, specialfunctions.h) when compiling my program, but still I get these undefined reference errors.
I'm using g++ on linux.
What am I doing wrong?
Thanks in advance.
You also need to include the binary part -- i.e., either the *.o files or the *.so library file -- on your final link line. So for example, you probably need to link with linalg.o .
Alglib needs to compile all 13 cpp files before using it.
I have CMakeList.txt to tare care all the dependencies for me.
I am trying to get PhysX working using Ubuntu.
First, I downloaded the SDK here:
http://developer.download.nvidia.com/PhysX/2.8.1/PhysX_2.8.1_SDK_CoreLinux_deb.tar.gz
Next, I extracted the files and installed each package with:
dpkg -i filename.deb
This gives me the following files located in /usr/lib/PhysX/v2.8.1:
libNxCharacter.so
libNxCooking.so
libPhysXCore.so
libNxCharacter.so.1
libNxCooking.so.1
libPhysXCore.so.1
Next, I created symbolic links to /usr/lib:
sudo ln -s /usr/lib/PhysX/v2.8.1/libNxCharacter.so.1 /usr/lib/libNxCharacter.so.1
sudo ln -s /usr/lib/PhysX/v2.8.1/libNxCooking.so.1 /usr/lib/libNxCooking.so.1
sudo ln -s /usr/lib/PhysX/v2.8.1/libPhysXCore.so.1 /usr/lib/libPhysXCore.so.1
Now, using Eclipse, I have specified the following libraries (-l):
libNxCharacter.so.1
libNxCooking.so.1
libPhysXCore.so.1
And the following search paths just in case (-L):
/usr/lib/PhysX/v2.8.1
/usr/lib
Also, as Gerald Kaszuba suggested, I added the following include paths (-I):
/usr/lib/PhysX/v2.8.1
/usr/lib
Then, I attempted to compile the following code:
#include "NxPhysics.h"
NxPhysicsSDK* gPhysicsSDK = NULL;
NxScene* gScene = NULL;
NxVec3 gDefaultGravity(0,-9.8,0);
void InitNx()
{
gPhysicsSDK = NxCreatePhysicsSDK(NX_PHYSICS_SDK_VERSION);
if (!gPhysicsSDK)
{
std::cout<<"Error"<<std::endl;
return;
}
NxSceneDesc sceneDesc;
sceneDesc.gravity = gDefaultGravity;
gScene = gPhysicsSDK->createScene(sceneDesc);
}
int main(int arc, char** argv)
{
InitNx();
return 0;
}
The first error I get is:
NxPhysics.h: No such file or directory
Which tells me that the project is obviously not linking properly. Can anyone tell me what I have done wrong, or what else I need to do to get my project to compile? I am using the GCC C++ Compiler. Thanks in advance!
It looks like you're confusing header files with library files. NxPhysics.h is a source code header file. Header files are needed when compiling source code (not when linking). It's probably located in a place like /usr/include or /usr/include/PhysX/v2.8.1, or similar. Find the real location of this file and make sure you use the -I option to tell the compiler where it is, as Gerald Kaszuba suggests.
The libraries are needed when linking the compiled object files (and not when compiling). You'll need to deal with this later with the -L and -l options.
Note: depending on how you invoke gcc, you can have it do compiling and then linking with a single invocation, but behind the scenes it still does a compile step then a link step.
EDIT: Extra explanation added...
When building a binary using a C/C++ compiler, the compiler reads the source code (.c or .cpp files). While reading it, there are frequently #include statements that are used to read .h files. The #include statements give the names of files that must be loaded. Those exact files must exist in the include path. In your case, a file with the exact name "NxPhysics.h" must be found somewhere in the include path. Typically, /usr/include is in the path by default, and so is the current directory. If the headers are somewhere else such as a subdirectory of /usr/include, then you always need to explicitly tell the compiler where to look using the -I command-line switches (or sometimes with environment variables or other system configuration methods).
A .h header file typically includes data structure declarations, inline function definitions, function and class declarations, and #define macros. When the compilation is done, a .o object file is created. The compiler does not know about .so or .a libraries and cannot use them in any way, other than to embed a little bit of helper information for the linker. Note that the compiler also embeds some "header" information in the object files. I put "header" in quotes because the information only roughly corresponds to what may or may not be found in the .h files. It includes a binary representation of all exported declarations. No macros are found there. I believe that inline functions are omitted as well (though I could be wrong there).
Once all of the .o files exist, it is time for another program to take over: the linker. The linker knows nothing of source code files or .h header files. It only cares about binary libraries and object files. You give it a collection of libraries and object files. In their "headers" they list what things (data types, functions, etc.) they define and what things they need someone else to define. The linker then matches up requests for definitions from one module with actual definitions for other modules. It checks to make sure there aren't multiple conflicting definitions, and if building an executable, it makes sure that all requests for definitions are fulfilled.
There are some notable caveats to the above description. First, it is possible to call gcc once and get it to do both compiling and linking, e.g.
gcc hello.c -o hello
will first compile hello.c to memory or to a temporary file, then it will link against the standard libraries and write out the hello executable. Even though it's only one call to gcc, both steps are still being performed sequentially, as a convenience to you. I'll skip describing some of the details of dynamic libraries for now.
If you're a Java programmer, then some of the above might be a little confusing. I believe that .net works like Java, so the following discussion should apply to C# and the other .net languages. Java is syntactically a much simpler language than C and C++. It lacks macros and it lacks true templates (generics are a very weak form of templates). Because of this, Java skips the need for separate declaration (.h) and definition (.c) files. It is also able to embed all the relevant information in the object file (.class for Java). This makes it so that both the compiler and the linker can use the .class files directly.
The problem was indeed with my include paths. Here is the relevant command:
g++ -I/usr/include/PhysX/v2.8.1/SDKs/PhysXLoader/include -I/usr/include -I/usr/include/PhysX/v2.8.1/LowLevel/API/include -I/usr/include/PhysX/v2.8.1/LowLevel/hlcommon/include -I/usr/include/PhysX/v2.8.1/SDKs/Foundation/include -I/usr/include/PhysX/v2.8.1/SDKs/Cooking/include -I/usr/include/PhysX/v2.8.1/SDKs/NxCharacter/include -I/usr/include/PhysX/v2.8.1/SDKs/Physics/include -O0 -g3 -DNX_DISABLE_FLUIDS -DLINUX -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp"
Also, for the linker, only "PhysXLoader" was needed (same as Windows). Thus, I have:
g++ -o"PhysXSetupTest" ./main.o -lglut -lPhysXLoader
While installing I got the following error
*
dpkg: dependency problems prevent configuration of libphysx-dev-2.8.1:
libphysx-dev-2.8.1 depends on libphysx-2.8.1 (= 2.8.1-4); however:
Package libphysx-2.8.1 is not configured yet.
dpkg: error processing libphysx-dev-2.8.1 (--install):
dependency problems - leaving unconfigured
Errors were encountered while processing:
*
So I reinstalled *libphysx-2.8.1_4_i386.deb*
sudo dpkg -i libphysx-2.8.1_4_i386.deb