I want to link my C++ executable to both a static (libStatic.a) and a shared (libShared.so) library, using a makefile.
The makefile so far has the following content:
myExe: main.cpp libStatic.a libShared.so
g++ main.cpp libStatic.a libShared.so
I'm fairly sure that the static linking is correct, as I have seen similar things elsewhere. What I am unsure of is the shared linking part. Is this correct? Or is linking to a static library done differently?
If I run make, then it seems to be ok, and creates the executable. However, when I execute this, I reveive the error:
/usr/bin/ld: cannot find -lShared
However, my executable and libShared.so are in the same directory.
You need to set LD_LIBARY_PATH to this directory where the shared object is sitting before you run your program.
You can read up on 'rpath' in man ld for other possibilities.
Related
I have a simle file main.cpp and static library MyLib.lib and I am trying to link program against static library like this:
g++ -o m main.cpp -static -L c:\lib\path -l MyLib
or like this:
g++ -o m main.cpp -L c:\lib\path -Wl,-Bstatic -l MyLib -Wl,-Bdynamic
The compilation process exits successfully and without error. However when I try to run m.exe from command line I get error that it cannot be run because MyLib.dll cannot be found.
I specificaly said it should compile against static lib MyLib.lib so why is it searching for a dynamic library? Did I made an error in commands above?
It really looks like you linked with a shared library.
You need to add the location of the folder containing MyLib.dll to the PATH.
In a Command Prompt type this:
SET PATH=<dll_location>;%PATH%
m.exe
or make sure MyLib.dll is in the same folder as m.exe.
If gcc only finds a shared library there is a chance the static flags didn't work.
Why is your library not called libMyLib.a? The name MyLib.lib seems to imply you got it prebuilt from MSVC. If so, how do you know MyLib.lib is not a shared library?
Is there a way you can build MyLib yourself as a static library?
I am trying to generate a c++ library using the g++ compiler. My library has another C library as dependency and I have compiled it in order to obtain the .so files.
I have the following structure:
src:
include/linux:
libcustom.a
libcustom.la
libcustom.so
libcustom.so.0
libcustom.so.0.0.0
Now, when I have all the .o files of my cpp classes, and I want to link the library, I execute the following command:
g++ -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -Wl,-z,relro -o mylibrary.so File1.o File2.o File3.o -L./include/linux -lc++ -lutil -lm -lcustom -Wl,-rpath='$ORIGIN/include/linux' -L/usr/lib/R/lib -lR
But it throws me the error:
libcustom.so.0: cannot open shared object file: No such file or directory
I am executing the command from the src directory.
I know it could be fixed editing the LD_LIBRARY_PATH, but the idea it is someone can use my library without the need of configuring anything, so I am trying to do that with the c++'s -rpath flag.
Any idea how can I fix it, or the reason for the error?
The error message you got seems to come from the run-time loader ld.so instead of the linker ld (I know the names are confusing). You have to distinguish between finding so's at link-time and at run-time. The -L flag you give at link-time has nothing to do with localizing the library at run-time.
Your rpath=./include/linux value is not correct, because dot is not recognized by the ld as relative path. Relative searching path should be given like
-Wl,-rpath='$ORIGIN/include/linux'
where the $ORIGIN represents the folder where your executable (not mylibrary.so) locates. Make sure to use single quote and not double quote because the string $ORIGIN should be passed to the linker literally and hard coded into the executable file.
More details goes
how to link to shared lib from shared lib with relative path
ld: Using -rpath,$ORIGIN inside a shared library (recursive)
I have built a GCC cross toolchain for the RPi and can cross-compile C++ source and successfully run it after copying the executable to the RPi.
Next I built the Boost libraries targeting ARM, using the cross toolchain. I can successfully build and link C++ source to those Boost libraries using the cross toolchain on my PC.
I then copied the program, dynamically linked to Boost, to the RPi and copied all built libraries into /usr/local/lib on the Pi. However, executing fails:
$ ./my_program
./my_program: error while loading shared libraries: libboost_system.so.1.60.0: cannot open shared object file: No such file or directory
Again, this library, libboost_system.so.1.60.0, exists in /usr/local/lib.
I also tried
export LD_LIBRARY_PATH='/usr/local/lib'
but that doesn't change anything. What am I doing wrong?
EDIT:
I build all source files like this (rpi-g++ is a symlink to my cross-compiler):
rpi-g++ -c -std=c++1y -Wall -Wextra -pedantic -O2 -I /path/to/cross/boost/include *.cpp
rpi-g++ -o myprog *.o -L /path/to/cross/boost/lib/ -lboost_system -pthread
EDIT 2:
When linked with
rpi-g++ -o myprog *.o -L /path/to/cross/boost/lib/ -rdynamic -lboost_system -pthread
the problem remains the same. I have checked and verified everything suggested by Technaton as well. Strangely, ldd insists that the created executable is "not a dynamic executable" (checked that on my PC and on the RPi), which doesn't make sense to me.
There are several things you can check. I've posted a complete check list here, but judging from your linker command line, number 5 is probably the culprit.
Check that your library and your program are correctly build for the target architecture. You can verify that by using file ./myprog and file libboost_system.so.1.60.0.
Make sure that you have copied the actual shared object, and not a link to it.
Ensure that the shared object file's permissions are sane (0755).
Run ldconfig -v and check that your shared object file is picked up. Normally, /usr/local/lib is in the standard library search path, and LD_LIBRARY_PATH is not required.
Make sure that your program is actually dynamically linked by running ldd ./myprog. Judging from your linker command line, that is the problem: You're missing -rdynamic.
Check the paths returned from ldd: If you have linked with rpath, the library search path might be screwed up. Try again without -rpath.
Is it possible to build a library that uses another, already compiled library?
I have some make files that are used to normally build an executable. When making the executable, I use -L ../include/lib1.a to include the original library.
Now, I am building a separate program that is calling the classes from the executable, which was never built into a library, just compiled to the executable with a link like
${CPP} -c ${INC} ${CFLAGS} MyFile.cpp ${OBJ} ${LIB2} -lm
Where LIB2 includes the reference to lib1.a
Now I want to access the class MyFile.cpp directly, and when I build it to its own library lib2.a, and try to call it from the new program, I get a bunch of errors that the classes it references are missing. This is in spite of the fact that when building the new program I am linking in both lib1.a and lib2.a
Should:
-L../include/lib1.a
not be:
-L../include -llib1
I.e. -L denotes the library search path and -l the archive name?
Yes, you should be able to do it. It would be helpful to see the exact errors you are getting.
If you compile your sources into a library and supply the libraries they use on the command line, the compiler is liable to put the other library(s) into your new one. If that happens, and then someone tries to build a program against your library and those others, they will get a whole mess of "doubly-defined symbol" errors.
When you build lib2.a it will not contain the objects files contained in lib1.a.
Your final executable has to link in both of them.
I would like to utilize the UnitTest++ library in a testing file. However, I am having some difficulty getting the library to be included at compile time. So here is my current directory structure:
tests/
UnitTests++/
libUnitTest++.a
src/
UnitTests++.h
unit/
test.cpp
I have just used the UnitTest++ getting started guide to just get the library setup. Here is test.cpp:
// test.cpp
#include <UnitTest++.h>
TEST(FailSpectacularly)
{
CHECK(false);
}
int main()
{
return UnitTest::RunAllTests();
}
And I am currently trying to compile with:
gcc -lUnitTest++ -L../UnitTest++/ -I../UnitTest++/src/ test.cpp
I am currently getting a bunch output with ld: symbol(s) not found at the end. So how would I be able to get the UnitTest++ library properly included when this program is compiled? I am on a Mac and I'd also like for there to be an easy way for people on a Linux machine to run these same tests.
Whew, I hope this provides enough information, if not please let me know.
I was able to build it in the following manner
gcc -L../UnitTest++/ -I../UnitTest++/src/ test.cpp -lUnitTest++ -lstdc++
or
g++ -L../UnitTest++/ -I../UnitTest++/src/ test.cpp -lUnitTest++
that links to libstdc++ automatically.
GCC documentation says:
-llibrary
-l library
Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified.
Thus, foo.o -lz bar.o' searches libraryz' after file foo.o but before bar.o. If bar.o refers to functions in `z', those functions may not be loaded.
I guess that's why the library symbols are not found when you first specify -lUnitTest++ and then test.cpp
Compile test.cpp to get test.o
and use
g++ test.o libUnitTest++.a -o ./exectest
to get the ./exectest executable
libUnitTest++.a is just an archive of all the object files of UnitTest++. You just need to link all the object files (your test object file + libUnitTest++.a)
Try editing the makefile that came with unittest++ and make it suitable for your case
The message ld: symbol(s) not found means you haven't compiled the library. So you need to go in the UnitTest++ folder, compile and install it.
I've never worked on a MAC, but in linux, libraries are usually compiled and installed with:
./configure
make
make install
In the UnitTest++ link you posted, you should simply:
make install
Then you will have the UnitTest++.so library in the libraries folder of your OS. Now the library can be linked with your program with the -lUnitTest++ command.
Usually you have to put -Lsomething before the -lsomething that requires it.