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Inspector - A drop-anywhere C++ REPL

Build Status

Allows to inject a fully-functional C++17 REPL into running, compiled programs that can access your program state and offers features like code-completion and syntax highlighting.

The API is similar to tools like Pry in Ruby or Pdb in Python:

Example program:

// save as main.cpp
#include <iostream>
#include <string>

int main(int argc, char** argv) {
    int a = 1;
    std::string b = "hello world";
#include INSPECTOR
    std::cout << "second break." << std::endl;
#include INSPECTOR
$ ./inspector prebuild main.cpp 
$ clang++ $(./inspector print-cflags) main.cpp -o main 
$ ./inspector repl
$ ./main

Inspector example session

Presentation slides on Inspector

10 min video presentation on Inspector

Cppcast about Inspector



  • a c++ compiler (gcc or clang++)
  • libcling (see installation instructions below)
  • jsoncpp
  • python3
  • python-prompt-toolkit (for python3)
  • python-setuptools (for python3)
  • pkg-config

Build Cling

Note that for some linux distributions the cling project also provide pre-build binaries.

git clone src
cd src
git checkout cling-patches
cd tools
git clone
git clone
cd clang
git checkout cling-patches
cd ../..
mkdir build inst
cd build
cmake -DCMAKE_INSTALL_PREFIX=../inst ..
cmake --build .
cmake --build . --target install

Build Inspector

git clone
cd inspector
mkdir build
cd build
cmake -DCMAKE_PREFIX_PATH="../inst" ..
cmake --build .


# bring python bindings
# (requires clang 5/trunk for python3 support, the clang branch from cling is new enough)
# and libclang into path
export PYTHONPATH=$(readlink -f <llvm-root>/src/tools/clang/bindings/python/)
export LD_LIBRARY_PATH=$(readlink -f <llvm-repo>/inst/lib)
cd build
./inspector prebuild ../test/test.cpp
gcc -o test-proc $(./inspector print-cflags) ../test/test.cpp
# start repl cli
./inspector repl
# let program connect to repl


  • buildsystem integration:
    • cmake
    • autotools
    • make
    • meson
  • include type declaration into the repl
  • search for '#include INSPECTOR' before parsing (speed)
  • use verbose mode of compiler to get additional include paths for cling / libclang parsing
  • multiprocessing scanning
  • GDB/LLDB plugin: link/preload and invoke inspector with debug information from gdb/lldb.
  • Support for more languages:
    • C
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