I would like to build a plain C console app in Xcode. I have 5 source files added to a project and a library, say libMyLib.a. The C source files obviously use the library. I can't get this to work, the linker produces errors of type :
Undefined symbols for architecture x86_64...
I have checked with lipo that the static library supports this architecture. I tried various options suggested on this forum: setting paths to headers (absolute, as well as using $(SOURCE_ROOT)), setting Build Phases -> Link Binary With Libraries, using workspaces. The same source code compiles fine when using command line gcc. I have also tried setting additional linker flags in Xcode to those that I use with make. Nothing works. What am I missing?
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I recently made a small library in C, and I wanted to put it together with the standard libraries so I don't have to always copy the files for each new project.
Where do I have to put it so I can import it like the standard libraries?
Compiler : MinGW
OS: Windows
You need to create a library, but you don't necessarily need to put it in the same place as MinGW's standard libraries (in fact I think that's a bad idea).
It is better to put your own library/libraries in specific place and then use the -I compiler flag to tell the compiler where to find the header files (.h, .hpp, .hh) and the -L linker flag to tell the linker where to find the library archives (.a, .dll.a). If you have .dll files you should make sure they are in your PATH environment variable when you run your .exe or make sure the .dll files are copied in the same folder as your .exe.
If you use an IDE (e.g. Code::Blocks or Visual Studio Code) you can set these flags in the global IDE compiler/linker settings so you won't have to add the flags for each new project.
Then when building a project that uses your library you will need to add the -l flag with the library name to your linker flags, but without the lib prefix and without the extension (e.g. to use libmystuff.a/libmystuff.dll.a specify linker flag -lmystuff). The use of the -static flag will tell the linker to use the static library instead of the shared library if both are available.
I have created a minimal example library at https://github.com/brechtsanders/ci-test to illustrate on how to create a library that can be build both as static and shared (DLL) library on Windows, but the same code also compiles on
macOS and Linux.
If you don't use build tools like Make or CMake and want do the steps manually they would look like this for a static library:
gcc -c -o mystuff.o mystuff.c
ar cr libmystuff.a mystuff.c
To distribute the library in binary form you should distribute your header files (.h) and the library archive files (.a).
I am attempting to run an old program that uses tcl as well as legacy opengl. I managed to link the opengl libraries successfully; however, I cannot seem to get the tcl linker to work. For context, the program I am using came with include and lib folder. The lib folder contains tclstub86_32.lib, tclstub86_64.lib, and tkstub86.lib as well as opengl .libs. The include folder contains two folders: tcl_include and tk_include, which obviously contain all the .c and .h files for tcl and tk. The following pictures show my settings from using project -> build options:
The error I receive when compiling is:
C:\Users\amlut\Downloads\C\tkogl\curve.c|18|undefined reference to `_imp__Tcl_Free'|
And here is the bit of code that is throwing the error:
if (*line != NULL) Tcl_Free((char*)*line);
I am not sure what I am doing wrong here, any help is appreciated. Thank you.
The problem is that the code is apparently linking against the Tcl stub library (an ABI/API adaptor library) but isn't compiling to use that library but rather to use a full Tcl library instead. When building an extension package, using the stub library is a good thing as it means that the resulting code is not bound to an exact version of the Tcl (and Tk) library but rather to a version of the Tcl ABI which has a much longer support cycle.
The fix is to define the USE_TCL_STUBS and USE_TK_STUBS (that has the identical issue; you have just hit the Tcl version of it first) C preprocessor symbols when building; set them both to 1 and recompile. This is done under the Compiler Settings tab in Code::Blocks apparently.
I am a relatively inexperienced C developer with no previous experience in integrating libraries made by other developers into existing projects.
Basically, I need a means of parsing JSON data in an AVR microcontroller for a university project. To this end I attempted to download and integrate jansson (https://github.com/akheron/jansson) into my existing build of the microcontroller code. I am working with Atmel Studio in Windows 10, but I have also installed Code::Blocks with MinGW GCC (on the same Windows 10 installation) for the purpose of building the library, and to attempt to integrate the library into a native Windows application. So far, neither has been successful, and I get the same errors. All of the online resources I've found so far have been to basic to be useful, or well beyond my comprehension.
This is what I have done thus far:
I began by attempting to build the software and then integrate it into an existing project per the instructions in https://jansson.readthedocs.io/en/2.11/gettingstarted.html. I installed CMake, built the project files for Code::Blocks with cmake.exe -G “CodeBlocks - MinGW Makefiles”, then opened the project and built everything. A few of the targets (I believe related to testing) failed to build, but jansson itself built and output libjansson.a to the \lib\ directory, so I didn’t think too much of it.
That is as far as I’ve been able to get. In both Atmel Studio and Code::Blocks, I do the same thing: add jansson.h to the relevant include paths, add #include “jansson.h” to all of the relevant files, and add libjansson.a as a library in each IDE’s respective linker options. I’ve tried various things like adding and removing flags to the linker, but the output is always “cannot find -ljansson”, “undefined reference to ‘json_object_seed’” (which is a function in the API I’m calling for no reason other than to see if the project has built properly) and/or “ld returned 1 exit status”.
I cannot help but feel as if the issue is with the line “cc -o prog prog.c -ljansson” in the documentation linked above. I really just don’t understand how to set up the linker properly to get the project to build.
If anyone could give some insight into what I’m doing wrong/the correct way to link this library I would appreciate it a lot.
The library itself should be built with appropriate toolchain. I assume that you built your library twice, one version using MinGW toolchain and other with avr-gcc toolchain.
If you compile target application and linker cannot find library, then try to add path of directory that contains *.a file of library to linker settings (linker search path). Let's say you have: /path/to/lib/libjansson.a
In Code::Blocks: Project → Build options → Search directories → Linker add /path/to/lib/. Then it should link with include path set, for example: cc -o prog prog.c -ljansson -L/path/to/lib/
In Atmel Studio when you add a library in Solution Explorer → Libraries → Add Library it should automatically add library search path to linker options. If you check Project → Properties → AVR/GNU Linker there should be (between other options): -Wl,-ljansson -Wl,-L"/path/to/lib/"
If you copied library files (libjansson.a and jansson.h) to your application's project directory, it will be convenient to use relative paths to library files.
In the process of porting a C project from Linux to Windows
Have installed MinGW
Have compiled my shared library using a Makefile
This produces libExample.so
Now I'm trying to link this shared library to a test harness so I can see if everything is working as expected
In the harness Makefile I specify the location of the library, e.g. -LE:/libExample_dir and the name of the library -lExample
but its complaining it cannot find the library, i.e. linker is failing with cannot find -lExample - is there some difference with windows regarding .so and .dll or perhaps pathnames that I am missing?
You need to fix the make file so shared libraries are generated with a .dll extension.
If I had to guess, I'd say that while renaming the generated file is enough to make the linker happy, the loader still expects the .so extension because that's the name that was compiled in...
Using MinGw to compile C code to produce a shared library, remember to rename the output from libExample.so to libExample.dll otherwise the linker will fail to find your library
I have 2 build environments with different versions of MinGW: one configured for Qt and one not. Both, however, have the stub static libraries of Qt (which end up actually linking to the dlls). The problem is that I want to build a static library in the Qt MinGW and then include it in the non Qt MinGW. I get the following link errors when I try:
moc_browser.cpp:(.eh_frame+0x11): undefined reference to `___gxx_personality_v0'
browser.cpp:(.text+0x213): undefined reference to `__Unwind_Resume'
I found that the Qt MinGW is linking dynamically to the standard libraries and that i need to include the option -static-libgcc. However, I do not know where to use it since I am not building an executable, but rather a static library.
A static library is just a collection of object files - an archive. You don't create it by linking, but with an archiving program (often ar). To include the object files of another static library in a new one, you have to find the relevant options for the archiving program to merge them.