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I get linking error like

$ g++ -o yyy atomic.cpp --std=c++11
/tmp/ccLVp09P.o: In function `std::atomic<std::shared_ptr<int> >::load(std::memory_order) const':
atomic.cpp:(.text._ZNKSt6atomicISt10shared_ptrIiEE4loadESt12memory_order[_ZNKSt6atomicISt10shared_ptrIiEE4loadESt12memory_order]+0x37): undefined reference to `__atomic_load_16'
collect2: error: ld returned 1 exit status

for code below

#include <iostream> 
#include <atomic>
#include <memory>

int main () {
  std::atomic<std::shared_ptr<int>> foo (std::shared_ptr<int>(new int(10)));
  std::cout << "foo: " << *foo.load() << '\n';
}

Environment:

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.9.2-0ubuntu1~14.04' --with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.9 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.9.2 (Ubuntu 4.9.2-0ubuntu1~14.04)

Strange thing that when I build 32-bit version g++ -o yyy atomic.cpp --std=c++11 -m32 everything works fine

It looks like some problem with my compiler/linker how to analyze and solve it?

triclosan
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  • Your code's not valid AFAIK, shared_ptr is not trivially copyable. – Mat May 05 '15 at 11:07
  • @Mat, yes i've read about `std::atomic` at this point, but anyway might it be root of linking problem? – triclosan May 05 '15 at 11:09
  • clang and g++ 5.1 give a much better diagnostic. Not sure why linking fails, g++ probably just emits code assuming some atomic operation exists when it doesn't. – Mat May 05 '15 at 11:11
  • Herb is pushing for `atomic>` (see [N4058](https://isocpp.org/blog/2014/06/n4058)), but I wouldn't count on it being already available. Even if you link with `-latomic` to resolve the missing symbol, you'll be in UB land. – DanielKO May 05 '15 at 13:43

0 Answers0