I am following a tutorial that takes me to this SDL page (https://www.libsdl.org/download-2.0.php). In there, I can see three things I can download:
Source code
Runtime Binaries
Development libraries
I am trying to make sense out of them. My understanding is this:
Source Code: Is the original code made by the creator of the SDL, not compiled into a library.
Runtime Binaries: I have no idea
Development libraries: Is the code but this time compiled into libraries. There are two versions because one was compiled in a way that works with the VC (Visual compiler) and the other one is compiled in a way that works with the gcc compiler.
What are the runtime binaries for?
I imagine these thee scenarios:
Source Code: I am writing my project and when I hit compile I compie what I wrote alone with the SDL source code.
Runtime binaries: ?
Development libraries: I set up my programming environment to recognize the libraries. Then I write my code and when I hit compile the compiler compiles my code and then the linker links my code and the SDL libraries together into an executable.
The runtime binaries / libraries are the files that your application needs to use at run-time to access the library functions. They are the files that contain the actual compiled code of the library that your application will call when it is executed.
Related
I'm trying to link to the OpenAL soft library as compiled with the Media Autobuild Suite, and I'm getting the following error from Visual Studio:
libopenal.a(source.cpp.o) : fatal error LNK1143: invalid or corrupt file: no symbol for COMDAT section 0xA
My application is in C++ and compiled directly in Visual Studio 2019 (however, with the VS2017 toolset). OpenAL soft is written in C++ but exposes a C interface, and the MAB Suite compiles using MinGW/gcc and generates a libopenal.a static library file.
I've read from multiple other questions such as From MinGW static library (.a) to Visual Studio static library (.lib) and How to use libraries compiled with MingW in MSVC? that object files compiled with different compilers are generally not compatible for C++ due to name mangling, but often are compatible with C linkage. Because C does not use name mangling, and because the ABI is (usually) OS-dependent, libraries with a C interface compiled on the same platform are generally compatible.
Nevertheless, I've been running into linker errors, namely the LNK1143 above. I've confirmed that the included headers use extern "C" { to hint C linkage and that the target platform (x64) is the same for both builds. I also linked to libgcc.a as this answer recommends, and did not get any linker errors for it.
Does this mean the claim that C interfaces are generally compatible across compilers is not true? Or is this a special case in which it's not working? If the latter, what could be causing the linking to fail? Would I have better luck if I recompiled as shared libraries (dlls) instead of static libraries (even if I still use MinGW's .a files instead of .lib)?
I cannot change compilers from MSVC for my main app. I intend to use more libraries from the MAB Suite in the future, so I'd prefer to stay with MinGW for those dependencies if possible because I don't want to recompile all 70+ by hand.
Any help is appreciated. Thanks in advance.
Mixing compilers is tricky and prone to issues.
In some very simple cases it may work, but there are definitely a number of cases where you will run in to issues, for example:
if the different components use different runtime libraries
if memory management is being mixed (e.g. forget about freeing memory allocated with malloc() in MSVC using free() in MinGW)
when using exception handling in C++
My advice to do it all with the same compiler (and even the same version of this compiler).
Specifically in your case OpenAL can be built with MinGW-w64. So maybe you should look into that instead of downloading some prebuilt version from the web.
Or - somewhat easier - use MSYS2 and use its pacman package manager to get its own MinGW-w64 build of OpenAL.
I figured out what works for me, so I'll share.
I was not able to link a static library between compilers as I originally attempted. My understanding is that the extra info kept in the lib to allow link-time code generation is compiler-specific. Brecht Sanders's answer outlines a few possible reasons why the code wouldn't be compatible.
I was, however, able to link to a shared library, with a few extra steps.
Using the same suite (see the question), I compiled as shared and got libopenal.dll, libopenal.dll.a, and libopenal.def. In my case, the .def file was generated by the suite. Accoding to this answer, you can generate a .def file with gcc using:
gcc -shared -o your_dll.dll your_dll_src.c -Wl,--output-def,your_dll.def
Trying to link to libopenal.dll.a still gave me errors (I don't know exactly why, and I already discarded the logs.) What I did instead was generate a .lib file from the .def file. In Visual Studio's built-in terminal:
lib /machine:x64 /def:libopenal.def
This generated a libopenal.lib file in the working directory. Linking to this file worked perfectly, and I was able to successfully load the dll at runtime.
I've tested this same method with many other MinGW-compiled libraries from the suite, including libavformat, libavcodec, libavutil, libavdevice, swresample, and swscale, and thus far all of them have worked.
Kind of convoluted, but it seems to work well for me, so I hope this helps anyone else with the same problem.
My question is as the topic.
I am currently using Mingw32 compiler in Qt creator to compile my application. The problem is that I include a .lib static library and header file which compiled from Visual Studio 2017 in my application.
When I further run or compiled my application in Qt. I would be facing the error code, unrecognized file format pointing to the .lib file.
I reasonably doubt that: For example, I can not use compiler 1 to compile other libraries compiled from compiler 2.
I follow the instruction here:libwdi Installation and Compilation to compile the "libwdi.lib" file.
FYI, the reason that I use Visual Studio to compile the .lib library(libWdi) is because it's easier to achieve on my Windows OS after I tried using wingw32-make from Qt5 Tool. It is such a pain since I can not even run ./autogen.sh to generate the makefile for Mingw32 on Windows.
Appreciate any step-by-step information on how to build a workable .lib file for Qt creator, including using VS, mingw, and cross-compilers.
If the target library uses c++ features in its public interface then it is likely this is not going to work regardless of what machinations you go through. Even different versions of the same compiler often have problems in that situation.
Pure C on the other hand will usually work (on Windows non-MS tool sets will be made to at least consume the MS intermediate object format, even if not used by the compiler/linker normally).
I am working on a project(for Windows) that is small and should be portable. I saw somewhere that MinGW gets rid of the requirement of some .dlls on the target system, so I thought I'd give it a try. To my suprise, when I tried running my program on a friend's computer, I got two errors saying that 2 different .dlls were missing. I thought MinGW used the system dlls, but it obviously didn't work. I saw an article on how to make a standalone exe with Visual Studio, but I'd prefer to use MinGW due to it's simplicity.
So my question: How to produce a standalone exe with MinGW?
Note: I am only using standard libraries, but it'd be nice to know how to include other libraries for future projects.
If you'd like an example of what I mean by a standalone exe, putty is a good example(it is an ssh client for Windows).
The two libraries you needed were most likely libgcc_s_sjlj-1.dll and libstdc++-6.dll or some variation of these, depending on how your mingw was configured when it was built. These are C and C++ standard library implementations.
If you want, you can pass extra flags to the compiler when you are linking the final executable, -static-libgcc and -static-libstdc++, which will cause it to link these libraries in statically instead of requiring you to distribute DLLs for them with your executable.
More info here: Mingw libgcc_s_sjlj-1.dll is missing
In general you can always try to statically link libraries into your executable. These special -static-libgcc flags are special flags provided only by mingw, not by other compilers, and not for other libraries, you use a different -static syntax for other libs. Static linking is fine but it gets more complicated and error prone as the dependencies get more complex. Static linking has some pitfalls associated to the order in which the libraries are linked. After a certain point, its usually simpler to make them all shared and don't do any static linking. It's up to you, it depends on how complex your project gets / if you start to have problems.
I am building a C++ application in Xcode 5 that links to external dynamic libraries (OpenCV 2.4.6, installed via macports). These dynamic libraries appear to have been compiled without debugging symbols, since, when I hit an error in them, I can't see the source code; all I see is assembly code.
I have separately downloaded the OpenCV source code from the OpenCV web site. Is there a way for me to tell Xcode where to look for the source files for the dylibs so that I can step through the OpenCV code in the Xcode debugger?
No, this isn't possible. When a library is compiled with debugging support, additional data is bundled into the shared library which contains a mapping along the lines of "address 0x00240008 corresponds to main.c:24", "address 0x0024001a corresponds to main.c:25", etc. If the modules were built without debugging support, the files are now simply binary blobs that contain machine code and the debugger has no way to translate the machine language back into the source code.
However, since you have the source code, you can recompile the library to include that information and install your custom version. For OpenCV, this will be a command like this:
cmake -DCMAKE_BUILD_TYPE:=Debug .
Im helping on a c++ application. The application is very large and is spread out between different sub directories. It uses a script to auto generate qt .pro files for each project directory and uses qmake to then generate make files. Currently the libraries are being compiled in alphabetical order.. which is obviously causing linking errors when a library its trying to link isn't built yet.. Is there some kind of g++ flag i can set so it wont error out if a library its trying to link hasn't been built yet? or a way to make it build dependencies first through the qt .pro file?
NOTE:
This script works fine on ubuntu 10.10 because the statements to build the shared libraries didnt require that i use -l(libraryname) to link to my other libraries but ubuntu 11.10 does so it was giving me undefined reference errors when compiling on 11.10.
Have you looked into using Qt Creator as a build environment and IDE? I've personally never used it for development on Ubuntu, but I have used it on Windows with g++, and it works great there. And it appears its already available as a package in the repository.
Some of the advantages you get by using it are:
Qt Creator will (generally) manage the .pro files for you. (If you're like me, you can still add lots of extra stuff here, but it will automatically add .cpp, .h, and .ui files as they are added to the project.)
You can set up inter-project dependencies that will build projects in whatever order they need to link.
You can use its integration with gdb to step through and debug code, as well as jump to the code.
You get autocomplete on Qt signals and slots, as well as inline syntax highlighting and some error checking.
If you're doing GUIs, you can use the integrated designer to visually layout and design your forms.
Referring back to your actual question, I don't think it's possible for a flag to tell gcc to not error when a link fails simply because there is no way for the linker to lazily link libraries. If its linking to static libraries (.a), then it needs to be able to actually copy the implementation of that code into the executable/library. If its dynamically linking (.so), it still needs to verify that the required functions actually exist in the library. If it can't link it during the linkage step, when can it link?
As a bit of an afterthought, if there are cyclic dependencies in your compile process (A depends on B, B on C, and C on A), then you might need to have a fake version of a library get built first, which only has empty stubs for the implementation of each function, and the full definition for each class or object. Then, build everything else while linking to that, and at the end, build the real version of the fake library, and link it to all the other versions that were already linked. I think this would only work on dynamic linking, though.
You could use a subdirs project to have control over the build order (no matter whether the other dev wants it or not :) ).
E.g.
build_all.pro
TEMPLATE=subdirs
CONFIG+=ordered
SUBDIRS=lib2/lib2.pro lib1/lib1.pro app/app.pro
The lib1.pro, lib2.pro, ... are your generated pro files.
Then run qmake once for the build_all.pro and also run make in that directory. This will build lib2 before lib1 and then app.