Undefined symbol: _ZN7QString13toUtf8_helperERKS_ at runtime

Undefined symbol: _ZN7QString13toUtf8_helperERKS_ at runtime

By : user2955560
Date : November 22 2020, 10:40 AM
it fixes the issue qmake/cmake is the way to go. But it is interesting to see how come linker succeeds and then during run, we get an undefined reference( not an unmatched dll case ). Especially since there is no preprocessor guard for toUtf8_helper in QT github repo. One more try. Can you add -DQT_COMPILING_QSTRING_COMPAT_CPP so that, we take slightly different path with the toUtf8() in #else part and not invoke the missing toUtf8_helper method.
Cause: I assume this happened since QtCore dll got built with a set of preprocessor flags which was not matched during the build of your project. Then the header files like qstring.h included in your code, which has inline functions, guarded with preprocessor definitions, as in for toUtf8() which is called during toStdString() will take a different path.
code :

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Why would a runtime undefined symbol be fixed by adding /usr/lib to ld.so.conf?

Why would a runtime undefined symbol be fixed by adding /usr/lib to ld.so.conf?

By : user2369724
Date : March 29 2020, 07:55 AM
around this issue In this particular case, the library was in /usr/lib, but also in with another project (and the linker was finding that one first). And it must have been a bad/incomplete one, since it was obviously missing a symbol.
I figured this out by running my program as
code :
LD_DEBUG=libs ./a.out
GCC Optimization results in "Undefined symbol" at runtime

GCC Optimization results in "Undefined symbol" at runtime

By : shereen khan
Date : March 29 2020, 07:55 AM
Hope this helps Is it possible that the header that defines the calling inline function includes the library's header without the extern "C" wrapper, and everywhere else the wrapper lines are used?
Did you try other levels like -O2?
Python C Extension using numpy and gdal giving undefined symbol at runtime

Python C Extension using numpy and gdal giving undefined symbol at runtime

By : epm
Date : March 29 2020, 07:55 AM
I hope this helps you . A Python extension module is a dynamically loadable (shared) library. When linking a shared library, you need to specify its library dependencies, such as -lgdal and, for that matter, -lpython2.7. Failing to do so results in a library with unresolved symbols, and if those symbols are not provided by the time it is loaded, the loading will fail, as reported by Python.
To resolve the error, you need to add libraries=['gdal'] to Extension constructor. Specifying -lgdal in extra_compile_args won't work because compile arguments, as the name implies, are used for compilation and not for linking.
Node app with C++ addon complains about undefined symbol at runtime

Node app with C++ addon complains about undefined symbol at runtime

By : Franky
Date : March 29 2020, 07:55 AM
This might help you There are a few things to check when linking a library and and then subsequently trying to load it. In Linux for example, all the symbols only need to be available at the final load stage (loading the executable), with node this will be when you run node and load the native addon. To force the node addon build to fail if there are missing symbols you must pass -z defs as a linker option in node-gyp. So you would add the following in your binding.gyp to the "link_settings" element or where appropriate:
code :
"ldflags": [
$ nm -C myaddon.node
$ ldd myaddon.node
$ pkg-config --libs opencv
$ pkg-config --cflags opencv
Runtime error using boost - undefined symbol: _ZN5boost6system15system_categoryEv

Runtime error using boost - undefined symbol: _ZN5boost6system15system_categoryEv

By : MercuryCCM
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further Whevener I link to boost with CMake I use FindBoost.cmake.
In your case it would be like this:
code :
find_package(Boost COMPONENTS thread) 
target_link_libraries(${LibName} Boost::thread)
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