1 symbol come from when using LLVM's libc++?
I see a fair amount of questions like Apple Mach-O Linker (Id) Error and Undefined symbols in cryptopp at IOS 64-bit project. The problem is usually described as:
Undefined symbols for architecture i386:
"std::__1::basic_ostream<char, std::__1::char_traits<char> >::flush()", referenced from:
cv::gpu::error(char const*, char const*, int, char const*) in opencv2(gpumat.o)
The problem often reduces to mixing/matching -stdlib=libc++ (LLVM C++ runtime) and -stdlib=libstdc++ (GNU C++ runtime). The LLVM C++ runtime ( libc++ ) has an __1 decoration symbol, but the GNU C++ runtime libstdc++ lacks the __1 symbol in its name. It causes linker problems for symbols that appears to have the same name (like std::string ).
Where does the __1 symbol come from when using LLVM's libc++?
Why was the problem not solved with a gnu namespace and an llvm namespace?
Here's a related question: libc++ - stop std renaming to std::__1?. But it kind of misses the point in that a rename does not occur.
It is from C++11 inlined namespaces
libc++ has something like
namespace std {
inline namespace __1 {
....
more at What are inline namespaces for?
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