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compex provides plugins for GCC and clang for extracting type information from C++.

The plugin itself dumps information about structures, fields and methods in YAML format, allowing you to easily build reflection facilities with C++.

A Python 3 helper script is included to convert to JSON if preferred.

You can also annotate structures, fields and methods with arbitrary tags.

Because compex is a compiler plugin, type information can be dumped as you compile files, eliminating the need to parse your source code twice and increase compile times.

Because compex uses the C++ compiler's parsing facilities, it understands all of C++, unlike tools such as Qt's moc, which can only parse limited subsets of C++.

compex is a very small codebase which can be easily customized or adapted. It may also serve as interesting reading for those interested in writing compiler plugins.

compex is entirely unrelated to C++ RTTI (dynamic_cast) and does not require it in any way.


Run make. If you only have one of gcc and clang installed, edit the Makefile and remove or (as appropriate) from the all target.

You may need to ensure that the header packages for GCC/clang are installed.

Run make install to install. The following are the default installation parameters, which you may override by passing them to make:

DESTDIR=                    # sandbox installation path

You can then run g++ or clang++ using the plugin directly:

g++ -c -fplugin=/usr/local/lib/ file.cpp
clang++ -c -Xclang -load -Xclang /usr/local/lib/ \
  -Xclang -plugin -Xclang compex_clang

or, after installation, using compex-config (recommended):

g++ -c `compex-config --gcc` file.cpp

For clang:

clang++ -c `compex-config --clang` file.cpp

compex output is sent to stdout by default. To redirect it to a file, pass -o filename to compex-config:

g++ -c `compex-config --gcc -o` file.cpp

You can alternatively pass -fplugin-arg-compex_gcc-o=filename directly to g++ or -Xclang -plugin-arg-compex_clang -Xclang -o=filename to clang++.

If you want to run compex without producing normal object code output, pass -S -o /dev/null to the compiler.

Example Input Programs; Example Output

See the doc/examples directory for example input programs and their corresponding output.


The header file <compex.h> provides macros for the use of the compex attributes. See compex.h for details.

Specify COMPEX_TAG() on any structure you want metadata to be dumped for. For example:

#include <compex.h>

struct COMPEX_TAG() my_struct {
  int x, y, z;

Metadata will be output for any structure with at least one COMPEX_TAG() tag. The COMPEX_TAG() macro expands to nothing when compex is not used.

You can also specify metadata to be attached to a construct using COMPEX_TAG(); simply pass a number of items to COMPEX_TAG(). Each should be an integer or a string literal. For example:

struct COMPEX_TAG("theAnswer", 42) my_struct {
  // ...

The arguments passed to COMPEX_TAG() become entries in a list in the output. If you specify COMPEX_TAG() multiple times for the same element, the arguments to each such tag are separate lists. A list is not emitted if no arguments are specified.

For example, if you specified COMPEX_TAG() COMPEX_TAG("a", "b", 42) COMPEX_TAG(1, 2, "c"), the 'tags' member of the output for the structure would look something like this:

  - - a
    - b
    - 42
  - - 1
    - 2
    - c

You can also use the GCC attributes directly, but this is not recommended:

struct __attribute__((compex_tag("foo"))) my_struct {
  // ...

compex currently uses the GCC attribute syntax instead of the C++11 attribute syntax due to what appears to be a bug in GCC, but this is all smoothed over by compex.h anyway.


The barebones script src/compex-convert can be used to convert the YAML output into JSON, if desired, or alternately into a format intended to be amenable to processing with the C preprocessor.


© 2014 Hugo Landau

File licenses vary due to the different licenses used by GCC/clang. See the end of each file for license information.

(Please note that licenses do not affect the output of compex, which can be used without restriction.)

Send bug reports or patches to


ℹ️ GCC/clang compiler plugins for the dumping of C++ type information in a machine-readable format






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