Since quite a while I noticed that I often cannot see data in the locals view. Such values are marked as "not accessible". Examples are std::string and boost::shared_ptr. Yesterday, I had a weird situation where I had a std::vector of boost::shared_ptr<SomeType> having entries in the vector which I could read and entries that were not accessible.

Today, I exemplarily tried to investigate the problem for std::string (C++11). I have found that in /usr/share/qtcreator/debugger/stdtypes.py there is a function qdumpHelper_std__string which has some kind of assertion:

d.check(0 <= size and size <= alloc and alloc <= 100*1000*1000)

This raises an exception due to this condition

alloc <= 100*1000*1000

Removing this condition makes the string visible in QtCreator - however, with some garbage at the end.

Some lines above this assertion there is this code:

# We can't lookup the std::string::_Rep type without crashing LLDB,
# so hard-code assumption on member position
# struct { size_type _M_length, size_type _M_capacity, int _M_refcount; }
(size, alloc, refcount) = d.split("ppp", data - 3 * d.ptrSize())

Now, when I debug the very same program using raw GDB I get the following structure ('s' is a std::string) which does not seem to match the above assumption:

(gdb) p/r s
$2 = {static npos = 18446744073709551615, _M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>}, 
 _M_p = 0x7fffffffe2b0 "bla"}, _M_string_length = 3, {_M_local_buf = "bla\000\377\177\000\000dSUUUU\000", _M_allocated_capacity = 140733199772770}}

Pretty-printing with GDB works:

(gdb) p s
$3 = "bla"

What's also strange is that _M_allocated_capacity (see GDB output above) has such a large value. Hence, I am not entirely sure whether this is a QtCreator problem at all.

Steps to reproduce:

1. Download the attached files CMakeLists.txt and testme.cpp.
2. Open QtCreator and load CMakeLists.txt as a project.
3. Configure the project for debug mode.
4. Add a command line argument for the program (e. g. "foo")
5. Set a break point in line 5 of testme.cpp
6. Run and debug
7. See that 's' is marked <not accessible>