I want to my make own library and have it use the same syntax as the standard C libraries as in
#include<mylib.h>
So that it looks like #include and some of the libraries that are included with C.
Can I make the library static as opposed to linking so that I can compile it in GCC without additional arguments, as if I were using another library like stdio.h or string.h?
This seems simple enough.
Develop the library (create as many source files as you need).
Build the source files into a shared library (.so) using a tool like CMAKE (which i strongly recommend).
Copy that library to your library path (i.e. /usr/lib)
Later on, all you have to do is import your lib: (i) in the source using #include<mylib.h>; (ii) when building (also using CMAKE) or using the flag (-lmylib) in the GCC compiler: gcc -lmylib myfiles.c -o myoutput.
In addition to #include "mylib.h", you need to add -lmylib command line to the compiler (more specifically linker) when using the library. I assume that the your library archive created through ar command is named as libmylib.a.
Usually, we do not write 'manually' build instructions, but we rely on tool that generates build chains. There are quite a lot of them, the most know are probably autotools and cmake (under Linux).
I would suggest you to have a look to cmake examples and/or documentation to get your code built.
There are quite a lot of differences between static and dynamic libs, and you will also need to package somehow your lib if you really want to use it like 'standard' lib (like libxml2, openssl, etc.)
A lot to say about it, but you should first have a look to 'how to build' your lib, and then see how to make it easy to use, IMHO.
Related
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 fairly new to C and I am trying to include a external library without using any IDE, only text-editor and the minGW compiler on windows cmd. The library is libPNG in this case, I would really like to understand how the process work not only for this library.
If there is a better way (and easier) to do this, I would also like to know.
You have two parts to take care of:
compilation,
linking.
Compilation
In compilation, when you transform source files in object files, your compiler must know what are the functions provided by the external library.
You could declare each function you use or you can include the library header file(s) in your code:
#incude <library_file.h>
It's not enough, you will have to tell your compiler where it can find this file:
-I<path_to_lib_folder> with gcc
/I<path_to_lib_folder> with cl (the visual studio compiler)
Linking
In linking process, you put the object and library files together to construct an executable file.
You need to tell the linker
what files it must use and
where it can find the library file
You tell the linker what files to use with the -l options, for instance, -lfoo will tell it to search for the libfoo.so lib
Note: with cl you can tell specify which library to use directly in your source code with #pragma comment (lib, "libfoo.lib")
Add you specify where with:
-L<path_to_lib_folder> with gcc
/LIBPATH:<path_to_lib_folder> with link (the visual studio linker)
You can also use dynamic linking, but let's start with the first step.
TL;DR - I need to compile archive.a with test.o to make an executable.
Background - I am trying to call a function in a separate library from a software package I am modifying but the function (a string parser) is creating a segmentation violation. The failure is definitely happening in the library and the developer has asked for a test case where the error occurs. Rather than having him try to compile the rather large software package that I'm working on I'd rather just send him a simple program that calls the appropriate function (hopefully dying at the same place). His library makes use of several system libraries as well (lapack, cblas, etc.) so the linking needs to hit everything I think.
I can link to the .o files that are created when I make his library but of course they don't link to the appropriate system libraries.
This seems like it should be straight forward, but it's got me all flummoxed.
The .a extension indicates that it is a static library. So in order to link against it you can use the switches for the linking stage:
gcc -o myprog -L<path to your library> main.o ... -larchive
Generally you use -L to add the path where libraries are stored (unless it is in the current directory) and you use -l<libname> to sepecify a library. The libraryname is without extension. If the library is named libarchive.a you would still give -larchive.
If you want to specify the full name of the library, then you would use i.e. -l:libname.a
update
If the libraypath is /usr/lib/libmylibrary.a you would use
-L/usr/lib -lmylibrary
How do I convince LibTools to generate a library identical to what gcc does automatically?
This works if I do things explicitly:
gcc -o libclique.dylib -shared disc.c phylip.c Slist.c clique.c
cp libclique.dylib [JavaTestDir]/libclique.dylib
But if I do:
Makefile libclique.la (which is what automake generates)
cp .libs/libclique.1.dylib [JavaTestDir]/libclique.dylib
Java finds the library but can't find the entry point.
I read the "How to create a shared library (.so) in an automake script?" thread and it helped a lot. I got the dylib created with a -shared flag (according to the generated Makefile). But when I try to use it from Java Native Access I get a "symbol not found" error.
Looking at the libclique.la that is generated by Makefile it doesn't seem to have any critical information in it, just looks to be link overloads and moving things around for the convenience of subsequent C/C++ compiler steps (which I don't have), so I would expect libclique.1.dylib to be a functioning dynamic library.
I'm guessing that is where I'm going wrong, but, given that JNA links directly to a dylib and is not compiled with it (per the example in the discussion cited above), it seems all the subsequent compilation steps described in the LibTools manual are moot.
Note: I'm testing on a Mac, but I'm going to have to do this on Windows and Linux machines also, which is why I'm trying to put this into Automake.
Note2: I'm using Eclipse for my Java development and, yes, I did import the dylib.
Thanks
You should be building a plugin and in particular pass
libclique_la_LDFLAGS = -avoid-version -module -shared -export-dynamic
This way you tell libtool you want a dynamically loadable module rather than a shared library (which for ELF are the same thing, but for Mach-O are not.)
I have to use LU decompostion to fit a simple model to some data (simulated) in C. An example of what I need to do is here:
However, I'm stuck with a more basic problem: how do I install packages in C and call them in my code?
I'm new in C and I'm used to R. But I have this assingment to do some tests about Matrix inversion, LU decomposision and the professor suggested using Lapack to easy things (thus, I don't need to code myself the LU decomposition etc.). But I don't know how to install the package and call it in my code, in order to use the functions of LAPACK.
I have a windows 7 64 bits and I'm using compiler Code Blocks 8.02
Thanks for any help.
Normally you don't "install" C libraries in that sense. Normally, in Windows you have three types of files. The header files, typically ending in .h, the dynamic library, .dll, and most likely some linker files (typically, .lib, .a or something). The linker and compiler will need to be able to find these files somewhere. Normally you set the include directory paths, and library directory paths.
E.g. Let's say you downloaded a library called foo, and you extract it to C:\foo.
In that folder, libfoo.a, foo.dll and foo.h reside. In Code::Blocks you will have to point include directory path to C:\foo and library path to C:\foo so that the linker and compiler know where to look for these files. Since you're linking against the foo library, you will also have to set -lfoo or something similiar in linker command line. This is GCC syntax, but I think Code::Blocks uses GCC compiler behind the scenes anyways.
In the C code you can just #include <foo.h> and the compiler will find it for you.
You need to install that library and it might actually supply a tool for that. Check their documentation (e.g. a file INSTALL or README in their distributed sources). If the library uses only headers you might only need to copy it's headers to some directory on your system, but their buildsystem might be able to do that for you.
Once that is done you would tell your IDE on where to look for the sources and if the library uses not just headers to link against the actual library file. See the documentation in the Code::Blocks Wiki on how this is done for some example cases and adapt for your library.
The simplest thing to do in your situation is to install Cygwin. You can use the setup.exe installer to install the GCC and the LAPACK libraries. When you want to use the LAPACK library, you will add the -llapack option to your GCC command line.