I am trying to work with the ffmpeg library on a cygwin development environment. I downloaded the shared build from here (64-bit). The bin folders contain dlls but no .a or .dll.a files. Linking, which is done like so:
$ gcc encoding_mp3.o -L/cygdrive/c/Users/Desktop/webserver/cygnus/lib/w32api -L/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_shared/bin -lavcodec-54 -lm -luser32 -lpthread -o encoding_mp3
results in the following error:
/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_shared/bin/avcodec-54.dll: file not recognized: File format not recognized collect2: ld returned 1 exit status
My question(s):
1. The bin/ folder in the shared build contains only avcodec-54.dll. Is there a way to convert the dll to a dll.a or .a?
2. Where am I going wrong?
If source code is required, please let me know.
You need to download the "dev" versions, or the "static linking" ones (a little down, on the page).
dlls cannot be converted to libs, nor can they be used (usually) to generate they own little import stubs (the .dll.a)
From the page you linked "Dev packages provide the headers and .lib/.dll.a files required to use the .dll files in other programs."
.a / .lib usually are located in "lib" folders.
Related
I have never worked with CMake before, so please forgive any rookie mistakes. Most of the following working frame has been given to me by my project group.
The goal is to build GoogleTest into a .dll, to be used in different, indepentent parts of our project. I'm having troubles setting up CMake the right way.
The work-flow so far has been:
Clone gtest from git --> also downloads a CMake List file
Alter variables in CMakeCache.txt to have it produce a Code::Blocks project file
Compile the project file in Code::Blocks
So far, it produces a static library (.a files) that can be used in our project. I'm having troubles genereating .dll files.
Variables I have tried changing:
BUILD_SHARED_LIBS:BOOL=ON --> the files generated by Code::Blocks now have a .dll.a double extension
CMAKE_C_FLAGS and all the corresponding C++ flags where set to -DGTEST_CREATE_SHARED_LIBRARY=1 as given here
CMAKE_EXE_LINKER_FLAGS has been set to -shared to make the linker produce .dll files
I have worked my way through the GoogleTest documentation here and here but in both, building it into a .dll is merely a 2-sentence-topic.
As #Tsyvarev pointed out, the .dll files were created in a (very) different folder.
I am using Header Only Libraries. The libraries are included through Cmake. I am using the g++ Compiler.
Now what I am looking for is to compile the c++ source files via windows cmd. In this moment i am using clion to compile.
Does anyone know how to compile the source files?
If i am compiling the files without cmake , I am getting errors because the program cannot find the libraries.
You do not run a source file, you run an executable produced by a compiler from source file(s)
If you are under a Linux for instance enter the path(s) where the libraries are through the environment variable LD_LIBRARY_PATH
[edit after your remark]
I mean compile
To indicate to g++ where the library are to link use the option -L followed by the path of a directory where the libraries are. If your libraries are on different directories use several time the option, one per directory
I'd like to link libpng found by pkg-config statically.
pkg-config --libs --static libpng
outputs
-L/usr/local/Cellar/libpng/1.6.15/lib -lpng16 -lz
I have both libpng16.a libpng16.dylib in that directory, and if I use these flags the library gets linked dynamically.
How can I tell either pkg-config or the linker (preferably in some portable-ish way) that I really want it linked statically?
I've tried adding -static before pkg-config's flags, but that makes clang's ld try and fail to link "crt0.o".
The pkg-config --static option relies on proper tagging in the .pc files. If providing the --static option does not return correct information necessary to link against the libpng archive, then you cannot use pkg-config for that purpose.
I suspect libpng (along with a majority of other packages) dropped support for static linking some time after libpng 1.2. They may still provide a library archive, but the libpng pkg-config file is no longer properly tagged to support a static link. You will have to manually tell ld to use the static lib.
Try:
-L/usr/local/Cellar/libpng/1.6.15/lib -l:libpng16.a -lz
Using -l with a : character allows you to specify the filename extension.
The -l: option is documented in the GNU ld 2.24 manual:
-l namespec
--library=namespec
Add the archive or object file specified by namespec to the list of files to link. This option may be used any number of times. If namespec is of the form :filename, ld will search the library path for a file called filename, otherwise it will search the library path for a file called libnamespec.a.
On systems which support shared libraries, ld may also search for files other than libnamespec.a. Specifically, on ELF and SunOS systems, ld will search a directory for a library called libnamespec.so before searching for one called libnamespec.a. (By convention, a .so extension indicates a shared library.) Note that this behavior does not apply to :filename, which always specifies a file called filename.
You could edit the .pc file to make it support static linking, especially if you are in a position to be compiling, patching, and installing software yourself instead of relying on some Linux distribution.
Here is an example of a .pc file that supports both dynamic and static linking. This is taken from /usr/lib/x86_64-linux-gnu/pkgconfig/xcb.pc on my Ubuntu system:
prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=${prefix}/include
xcbproto_version=1.11
Name: XCB
Description: X-protocol C Binding
Version: 1.11.1
Requires.private: pthread-stubs xau >= 0.99.2 xdmcp
Libs: -L${libdir} -lxcb
Libs.private:
Cflags: -I${includedir}
If you run pkg-config --libs xcb, it assumes you want the dynamic version and it gives you just -lxcb. The xcb.so dynamically shared object will know how to load all of its own dependencies so you don't have to specify them when linking against it.
If you run pkg-config --libs xcb --static, then the .private fields come into play, and you get -lxcb -lXau -lXdmcp.
I have not encountered many build systems that know to pass the --static argument to pkg-config. So if your .pc file is only intended to support static linking, it's probably best to not use .private fields, and just provide all the dependencies people will need unconditionally. That way people can link against the library successfully even if they don't know it's static or don't know to pass --static to pkg-config.
Just adding to the post by #David Garyson above I would like to add . If a particular
*.pc file is unavailable with the command
pkg-config --libs
then you might need to add a variable to your PATH
Perhaps you should add the directory containing `nice.pc' to the PKG_CONFIG_PATH environment variable
I use this trick in my Makefile.
LIBRARIES := $(shell pkg-config --libs libpng | sed -E 's/-l([a-z0-9]*)/-l:lib\1.a/g')
It grabs output from pkg config and expands it by prefixing each item with : and the lib, and post-fixing it with an .a. The end result is just what you need
-l:libpng.a -l:libz.a
I've been trying to create a CMake-based build-system for a project that is supposed to use SDL2_image library. I do not want to force user to install any libraries to the system to be able to build the project, so I took advantage of the CMake's ability to download and build dependencies (freetype, SDL2 and SDL2_image) from source code as External Projects.
Everything is fine with freetype and SDL2 (which both include CMakeLists.txt files out of the box), but I've ran out of ideas how to make it work for SDL2_image. CMake's external projects support custom configuration and building settings which I used in different variants with no success.
The CMake file itself can be found here, but the problematic part is this:
# SDL_image library
ExternalProject_Add(sdl2_image_project
URL https://www.libsdl.org/projects/SDL_image/release/SDL2_image-2.0.0.tar.gz
DEPENDS sdl2_project
PREFIX ${LIBS_DIR}/SDL2_image
CONFIGURE_COMMAND LDFLAGS=-L${SDL2_BIN} CFLAGS=-I${SDL2_SRC}/include SDL2_CONFIG=${SDL2_BIN}/sdl2-config <SOURCE_DIR>/configure --prefix=<INSTALL_DIR> --enable-shared=no
BUILD_COMMAND make
INSTALL_COMMAND ""
)
An error occurs while building sdl2_image_project. Some trivial research discovered that the error is generated by the undefined references to parts of libdl. Here is a tiny part of the hole error:
libtool: link: gcc -I/home/snikitin/_src/img_glypher/libs/SDL2/src/sdl2_project/include -I/usr/local/include/SDL2 -D_REENTRANT -o showimage showimage.o -Wl,-rpath -Wl,/usr/local/lib -pthread -L/home/snikitin/_src/img_glypher/libs/SDL2/src/sdl2_project-build ./.libs/libSDL2_image.a -L/usr/local/lib -lSDL2 -pthread
/home/snikitin/_src/img_glypher/libs/SDL2/src/sdl2_project-build/libSDL2.a(SDL_dynapi.c.o): In function `get_sdlapi_entry':
/home/snikitin/_src/img_glypher/libs/SDL2/src/sdl2_project/src/dynapi/SDL_dynapi.c:227: undefined reference to `dlopen'
I think the problem takes place due to the fact that linker tries to create a shared version of SDL2_image library while linking it to a static libSDL2.a. The thing is - if this is right - SDL2 building step creates both static and shared versions of itself so one would assume that linker would use libSDL2-2.0.so instead (I do not actually need a shared library - just the static one, but I do not know how to prevent the build system from trying to create it apart from passing --enable-shared=no to SDL2_image configure script, which does not help in this case).
After a lot of googling I've discovered that the possible source of the problem is that sdl2-config (which is called to get some flags for compiler during SDL_image building) may be called with wrong arguments and produces wrong cflags which confuse everything else. But I'm not sure that is the case and also I do not know how to influence sdl2_config call from CMake (configure --help does not seem to unveil any useful options for this situation).
I am running Ubuntu 14.04 x64 if it matters in any way. Would appreciate any advice!
Looks like you need to link some libraries like m and dl. It can be fixed by providing
custom sdl2-config file. Copy sdl2-config from extracted archive and substitute --libs result:
--libs)
echo -L${exec_prefix}/lib -Wl,-rpath,${libdir} -pthread -lSDL2 -lm -ldl
;;
Note that order is important (that's why just modifying LIBS not works for me).
Now this file can be used in your ExternalProject_Add command instead of SDL2_CONFIG=${SDL2_BIN}/sdl2-config:
...
... CFLAGS=-I${SDL2_SRC}/include SDL2_CONFIG=${CMAKE_CURRENT_LIST_DIR}/sdl2-config <SOURCE_DIR>/configure
...
I am trying to run cmake to generate makefiles. In the minimum working example, I have three files and 1 build directory.
File 1 is CMakeLists.txt, containing exactly:
add_library (MathFunctions SHARED mysqrt.cxx)
install (TARGETS MathFunctions LIBRARY DESTINATION lib)
File 2 is MathFunctions.h containing the function prototype, function relates to mysqrt.cxx.
File 3 is mysqrt.cxx containing include statement and a function definition.
When I create a build sub-directory and run "cmake ..", I am getting
CMake Error at CMakeLists.txt:2 (install):
install Library TARGETS given no DESTINATION!
Isn't my add_library, then install statement grammar correct? If I remove both SHARED and LIBRARY, cmake builds without errors.
Thanks for your help.
The problem is likely down to you running this on what CMake calls a "DLL platform" and how CMake classifies a shared library on such a platform.
From the docs for install:
For DLL platforms the DLL part of a shared library is treated as a RUNTIME target and the corresponding import library is treated as an ARCHIVE target. All Windows-based systems including Cygwin are DLL platforms.
So, try changing your command to something like:
install (TARGETS MathFunctions
ARCHIVE DESTINATION lib
LIBRARY DESTINATION lib
RUNTIME DESTINATION bin)