c++ - How to pretty-print STL containers in GDB?

Question

I've followed the instructions on the GDB wiki to install the python pretty-printers for viewing STL containers. My ~/.gdbinit now looks like this:

python 
import sys 
sys.path.insert(0, '/opt/gdb_prettyprint/python') 
from libstdcxx.v6.printers import register_libstdcxx_printers 
register_libstdcxx_printers (None) 
end 

However, when I run GDB and attempt to print an STL type, I get the following:

print myString
Python Exception <class 'gdb.error'> No type named std::basic_string<char>::_Rep.: 
$3 = 

Can anyone shed some light on this? I'm running Ubuntu 12.04, which comes with GDB 7.4.

Answer 1

It just works on Ubuntu 17.04

Debian seems to have finally integrated things properly now:

main.cpp

#include <map>
#include <utility>
#include <vector>

int main() {
    std::vector<int> v;
    v.push_back(0);
    v.push_back(1);
    v.push_back(2);
    std::map<int,int> m;
    m.insert(std::make_pair(0, 0));
    m.insert(std::make_pair(1, -1));
    m.insert(std::make_pair(2, -2));
}

Compile:

g++ -O0 -ggdb3 -o main.out -std=c++98 main.cpp

Outcome:

(gdb) p v
$1 = std::vector of length 3, capacity 4 = {0, 1, 2}
(gdb) p m
$2 = std::map with 3 elements = {[0] = 0, [1] = -1, [2] = -2}

We can see that the pretty printer is installed with:

(gdb) info pretty-printer

Which contains the lines:

global pretty-printers:
  objfile /usr/lib/x86_64-linux-gnu/libstdc++.so.6 pretty-printers:
  libstdc++-v6
    std::map
    std::vector

The printers are provided by the file:

/usr/share/gcc-7/python/libstdcxx/v6/printers.py

which comes with the main C++ library package libstdc++6 and is located under libstdc++-v3/python/libstdcxx in the GCC source code: https://github.com/gcc-mirror/gcc/blob/gcc-6_3_0-release/libstdc%2B%2B-v3/python/libstdcxx/v6/printers.py#L244

TODO: how GDB finds that file is the final mistery, it is not in my Python path: python -c "import sys; print(' '.join(sys.path))" so it must be hardcoded somewhere?

Custom classes

See how to define a custom toString method and call it at: Printing C++ class objects with GDB

Inspect specific elements in optimized code

It was hard last time I checked, you get "Cannot evaluate function -- may be in-lined" C++, STL, GDB: Cannot evaluate function maybe inlined

On unoptimized code it works: Inspecting standard container (std::map) contents with gdb