c++ - How to debug C++11 code with unique_ptr in DDD (or gdb)?

Question

std::unique_ptr are nice, but I find them less comfortable when debugging in DDD or gdb.

I'm using the gdb pretty printers that are part of gcc (e.g., /usr/share/gcc-4.8.2/python/libstdcxx/v6/printers.py). That is a big win for readability, for example:

$ print pTest
std::unique_ptr<MyType> containing 0x2cef0a0

However, dereferencing the pointer does not work:

$ print *pTest
Could not find operator*.

When I need to access the value, I have to manually copy the pointer and cast it to the correct type, for example:

print *((MyType*) 0x2cef0a0)

If the process is still running, this version works (still ugly but better):

print *pTest.get() // will not work if analyzing a core dump

The straightforward approach to Display *pTest in DDD does not work either. It only results in the following error:

<error: Could not find operator*.>

Is there a way to debug C++11 code with unique_ptr in DDD (without breaking the workflow like I do with my cumbersome workarounds)?

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I'm not afraid to use gdb commands, but DDD integration would be a plus. For example, following pointers in data structures by just double-clicking on them is often faster than typing.

I already tried to drop the pretty printer, but it is also not optimal. The best that I could come up with is the following:

 print pTest._M_t->_M_head_impl

Answer 1

This problem is actually not related to C++11, unique_ptr or pretty printing. The problem is that gcc does not emit code for std::unique_ptr::operator* that could be called by gdb to dereference the unique_ptr. If you for instance add *pTest; to your code then gdb does perform the dereferencing.

A similar problem is described in the SO post How to `print`/evaluate c++ template functions in gdb. Almost the same problem is described for an auto_ptr at https://sourceware.org/ml/archer/2012-q1/msg00003.html. If I understand the thread correctly one workaround would be to patch the pretty printer and also print out the dereferenced pointer when printing the unique_ptr. A gdb bug report can be found at http://sourceware.org/bugzilla/show_bug.cgi?id=12937.

The gdb wiki at https://sourceware.org/gdb/wiki/STLSupport describes more pretty printing solutions, which could have other workarounds.

Edit: A more elegant solution forcing the compiler to emit code for all member templates including operator* is to explicitly instantiate the class:

template class std::unique_ptr<MyType>;