Too many constructor characters

Question

When compiling this:

template <typename T> struct ConstArray { ///MEMBERS T* data_; T* end_; ///Constructors ConstArray(T* data, T* end) : data_(data), end_(end) {} }; template struct ConstArray<const char>; 

gives me ( nm -C *.o ):

 0000000000000000 W ConstArray<char const>::ConstArray(char const*, char const*) 0000000000000000 W ConstArray<char const>::ConstArray(char const*, char const*) 0000000000000000 n ConstArray<char const>::ConstArray(char const*, char const*) 

It seems that I get three characters (2 W + 1 n (I don't know what it is)) for each constructor defined. The functions seem to give me only one as expected. Can someone explain why this is or point me to an explanation?

Answer 1

Perhaps I see why these characters appear in nm output, but I can’t say whether it should / should not and what exactly n means. Maybe if someone is familiar with this, he can post the full answer.

If you do objdump -t ./obj.o , you will see a character table. With the exception of 2 constructors and many other characters, I see

 00000000 l .group 00000000 _ZN10ConstArrayIKcEC5EPS0_S2_ 

there. The flag is only l , which means that it is local, not debug, so I see it in nm as the third character.

If I do nm -g ./obj.o to see only external characters, I see only 2 W constructors, and when I do nm -a ./obj.o , I see all the characters as well as those marked in objdump -x like debug . And I also see there some debugging symbols that are n flagged in nm -a output.

So I don’t know what n means, but the third character is somehow related to the .group section of the elf file. Which is responsible for grouping characters together.