C++ Debug Window showing "<incomplete type> for string variable

Question

To my knowledge I'm initializing a string a fairly normal way and when I debug, the variables window in my IDE (CLion) shows its value as <incomplete type>. I have some simple code that results in the issue for the string variable Bob.

#include <iostream>

int main() {
    std::string Bob = "this doesn't show up in the variables window";
    std::cout << Bob << std::endl;
    return 0;
}

I don't know what impact it has but I'll include the CMakeLists file that appears to be the simplest that I can use.

cmake_minimum_required(VERSION 3.8)
project(testing123)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11"}

set(SOURCE_FILES main.cpp)
add_executable(testing123 ${SOURCE_FILES})

set(CMAKE_CXX_COMPILER "/cygdrive/c/cygwin64/bin/clang++")
set(CMAKE_C_COMPILER "/cygdrive/c/cygwin64/bin/clang++")

I looked at the other questions and they all had to do with classes and pointers which I can't see to be directly related, so if they are to blame for this, I'd appreciate an explanation as to how that would be.

Sound

We cannot try compiling the above, because (for starters) we do not have the various #include files. Please post a minimal, complete, and verifiable program.stackoverflow.com/help/mcve – Sinfonia

I've posted something that replicates the problem without the excess. – Sound

#include <string> ? – Kolnos

Unfortunately #include <string> appears to have no effect, Matt – Sound

Answer 1

You might need to set debug mode using _GLIBCXX_DEBUG macro.

You can do this in a CMakeLists.txt file with the following line:

set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_GLIBCXX_DEBUG")

Culpable

Answer 2

Using a standard library with debug symbols

On Linux, a less intrusive way than to recompile your whole source code with _GLIBCXX_DEBUG is to define

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/debug/libstdc++.so.6

for your debugger or IDE. You may have to install it via

sudo apt install libstdc++6-8-dbg

first. On Ubuntu, where I get CLion via Snap, I then replaced the symlink at /snap/bin/clion with a file that contains

#!/bin/bash
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/debug/libstdc++.so.6 /usr/bin/snap run clion "$@"

Now I can see the contents of strings, at least in LLDB (I didn't try GDB).

Hack

For GDB, a very quick workaround without any preparation is to cast a string to char*:

(gdb) p (char*) my_string
$13 = 0x2058970 "These are the contents"

This also works in CLion out of the box.

Downhill