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Geting correct compiler flags

There are multiple options to configure the plugin in such a way that everything works without major pain. This document outlines all these ways.

Prefer CMake and Sublime Text projects

The preferred way is to use Sublime Text project to organize your code and to use CMake as your build system. This way the plugin should work out of the box. See details below.

All flag sources from settings and external

There are three major sources for flags:

  1. Flags defined in settings of ECC.
  2. Flags generated from a flag source defined in flags_sources settings.
  3. Flags generated from the compiler.


The flags defined in settings are always used when compiling a new translation unit. They are appended to the ones generated from the external sources. Note, that the settings follow a hierarchy described in detail here.

Flags defined in settings

If you want to set the flag sources manually you can do it using the settings. However, I strongly suggest to NOT do this and use a proper build system instead. It will save you enormous amounts of time configuring the needed include flags. However, if you know what you're doing, the main sources of flags in settings:

  • Flags defined in the common_flags setting - flags added to each compilation of every file. See the link for an example.
  • Flags defined in the lang_flags setting - flags added to each compilation in addition to the common_flags but only for a specific language.

Flags defined in external flags sources

EasyClangComplete can search for CMakeLists.txt and generate a compile_commands.json file from it. See next section for details on how this file is parsed.

To use CMake way of generating flags, make sure you set the "flags_sources" in your settings. See how to set this setting correctly here.

Using a compilation database compile_commands.json

This file defines the flags per target (read more about it here). When this file is found, EasyClangComplete reads it and finds appropriate target given the file which is currently opened by the user.

Example compile_commands.json file (click to expand)

json tab="compile_commands.json" [ { "directory": "/main_dir", "command": "c++ -I/lib_include_dir -o CMakeFiles/main_obj.o -c /home/user/dummy_main.cpp", "file": "/home/user/dummy_main.cpp" }, { "directory": "/lib_dir", "command": "c++ -Dlib_EXPORTS -fPIC -o CMakeFiles/lib_obj.o -c /home/user/dummy_lib.cpp", "file": "/home/user/dummy_lib.cpp" } ]


The compile_commands.json does not contain header files. To complete header files we need to map them to an appropriate source file. By default, the plugin will try to search for the source file with matching name in the same folder as the header file. If this is not enough, use the setting header_to_source_mapping (details) in order to define a better mapping from header files to source ones.

Using .clang_complete file

This is a simple text file where each line defines a single flag. Don't forget, that you must specify the flags fully here. The paths that are not absolute will be expanded from the location of the .clang_complete file. The same wildcards as in settings can be used here too.

Example .clang_complete file (click to expand)

tab=".clang_complete" -I~.config/sublime-text-3/Packages/EasyClangComplete/src -I~.config/sublime-text-3/Packages/EasyClangComplete -Ilocal_folder -Wabi -std=c++14

The first two lines will have ~ expanded to your home directory, local_folder will be appended to the location of the .clang_complete file, other flags will be keps intact.

Flags generated from the compiler

Some flags can be generated from the compiler. These are governed by two settings: use_default_includes and target_compilers. These will run some command over a chosen compiler, parse the result for the flags specific to the compiler and will append these flags to the other ones. Click on the setting names above to read more about them.

Configurations that require manual actions

Some configurations cannot be configured without the knowledge that only the end user has. These usually include cases when the code generates files that must be included for proper code completions or when additional paths need to be provided to CMake when it is used as part of some other tool.

Below we will provide a list of the ones most commonly used.

Catkin setup (click to expand)

Catkin configuration

For those using Catkin (e.g. when developing with ROS) the plugin will configure the needed settings automatically if you are using Sublime Text projects. Here is a summary of what the plugin does for you. By default when running Sublime Text from GUI it knows nothing about the paths set in .bashrc of your system and therefore it cannot source your devel workspaces for you. Essentially sourcing the workspaces extends paths that Catkin uses to pass to CMake. So the plugin needs to update the CMAKE_PREFIX_PATH manually to be able to find catkin. Your *.sublime-project will look something like this after the configuration:

json tab="*.sublime-project" "ecc_flags_sources": [ { "file": "CMakeLists.txt", "prefix_paths": [ "/opt/ros/indigo", "~/catkin_ws/devel" ] }, ]


This will only work if you are using Sublime Text projects with your code. Otherwise no configuration will take place and the proper compiler flags will NOT be generated. You can set these settings also in yout User settings dropping the ecc_ prefix, but this is not a recommended.

Qt setup (click to expand)

Qt configuration

If you use Sublime Text for your Qt development and you use MOC files, you will need some additional setup. MOC generates header and source files from your *.ui files. These files are generated in the build folder of your project. As ECC uses a custom temporary location for your projects' CMake configuration it does not know about the real build location for your code (we might change this in the future, but this is the state for now). You will need to provide the build folder location in your flags.

The best way to do this is to modify the ecc_common_flags setting in your Sublime Text project file (*.sublime-project). You will need to add a new include flag with the path to your build folder.


For the sake of example let's consider that your project my_project gets built in a folder ~/YourBuildFolder/my_project. Also, your code lies in src folder within the project. Then you will want to add the following include to your settings:

            // Don't forget your other includes!

This way ECC will add this path as an include path when compiling your code and will be able to find the header files generated by the MOC system.

Tip: use wildcards!

Configuration is much easier if you use the available wildcards such as the $project_name seen in the example above. For a full list of available wildcards, see the wildcards section on the settings page.

Tip: clean project after changing this setting

If changing the setting does not work, make use of the Clear CMake cache command as ECC might still be using a cached version of the flags.


In my experience, the setting ecc_use_target_compiler_built_in_flags sometimes interferes with properly building Qt projects. So I recommend setting it to false:

"ecc_use_target_compiler_built_in_flags": false,