One of the core components of dds is that of the toolchain. A toolchain encompasses the environment used to build and link source code, including, but not limited to:

  1. The executable binaries that constitute the language implementation: Compilers, linkers, and archive managers.

  2. The configuration of those tools, including most options given to those tools when they are invoked.

  3. The set of preprocessor macros and language features that are active during compilation.

When a build is run, every file in the entire tree (including dependencies) will be compiled, archived, and linked using the same toolchain.

This page provides an introduction on how one can make use of toolchains most effectively in your project.


IMPORTANT: dds will not automatically load the Visual C++ environment. To use Visual C++, dds must be executed from the appropriate environment in order for the Visual C++ toolchain executables and files to be available.

Passing a Toolchain

In dds, the default format of a toolchain is that of a single JSON5 file that describes the entire toolchain. When running a build for a project, the dds executable will look in a few locations for a default toolchain, and generate an error if no default toolchain file is found (Refer to Providing a Default Toolchain File). A different toolchain can be provided by passing the toolchain file for the --toolchain (or -t) option on the command line:

$ dds build -t my-toolchain.json5

Alternatively, you can pass the name of a built-in toolchain. See below.

Built-in Toolchains

For convenience, dds includes several built-in toolchains that can be accessed in the --toolchain command-line option using a colon : prefix:

$ dds build -t :gcc

dds will treat the leading colon (:) as a name for a built-in toolchain (this means that a toolchain’s filepath may not begin with a colon).

There are several built-in toolchains that may be specified:


Uses the default gcc and g++ executables, linkers, and options thereof.

:gcc-N (for some integer N)

Equivalent to :gcc, but uses the gcc-N and g++-N executables.


Equivalent to :gcc, but uses the clang and clang++ executables.

:clang-N (for some integer N)

Equivalent to :clang, but uses the clang-N and clang++-N executables.


Compiles and links using the Visual C++ toolchain.

The following pseudo-toolchains are also available:


Uses built-in toolchain :XYZ, but generates debugging information.


Uses built-in toolchain :XYZ, but prefixes all compile commands with ccache.

:c++UV:XYZ (for two integers UV)

Sets the C++ version to C++UV and uses the :XYZ toolchain.

Providing a Default Toolchain File

If you do not wish to provide a new toolchain for every individual project, and the built-in toolchains do not suit your needs, you can write a toolchain file to one of a few predefined paths, and dds will find and use it for the build. The following directories are searched, in order:

  1. $pwd/ - If the working directory contains a toolchain file, it will be used as the default.

  2. $dds_config_dir/ - Searches for a toolchain file in dds’s user-local configuration directory (see below).

  3. $user_home/ - Searches for a toolchain file at the root of the current user’s home directory. ($HOME on Unix-like systems, and $PROFILE on Windows.)

In each directory, it will search for toolchain.json5, toolchain.jsonc, or toolchain.json.

The $dds_user_config directory is the dds subdirectory of the user-local configuration directory.

The user-local config directory is $XDG_CONFIG_DIR or ~/.config on Linux, ~/Library/Preferences on macOS, and ~/AppData/Roaming on Windows.

Toolchain Definitions

Besides using the built-in toolchains, it is likely that you’ll soon want to customize a toolchain further. Further customization must be done with a file that contains the toolchain definition. The most basic toolchain file is simply one line:

    compiler_id: "<compiler-id>"

where <compiler-id> is one of the known compiler_id options (See the toolchain option reference). dds will infer common suitable defaults for the remaining options based on the value of compiler_id.

For example, if you specify gnu, then dds will assume gcc to be the C compiler, g++ to be the C++ compiler, and ar to be the library archiving tool.

If you know that your compiler executable has a different name, you can specify them with additional options:

    compiler_id: 'gnu',
    c_compiler: 'gcc-9',
    cxx_compiler: 'g++-9',

dds will continue to infer other options based on the compiler_id, but will use the provided executable names when compiling files for the respective languages.

To specify compilation flags, the flags option can be used:

    // [...]
    flags: '-fsanitize=address -fno-inline',


Use warning_flags to specify options regarding compiler warnings.

Flags for linking executables can be specified with link_flags:

    // [...]
    link_flags: '-fsanitize=address -fPIE'

Toolchain Option Reference

Understanding Flags and Shell Parsing

Many of the dds toolchain parameters accept argument lists or shell-string lists. If such an option is given a single string, then that string is split using the syntax of a POSIX shell command parser. It accepts both single ' and double " quote characters as argument delimiters.

If an option is given a list of strings instead, then each string in that array is treated as a full command line argument and is passed as such.

For example, this sample with flags:

    flags: "-fsanitize=address -fPIC"

is equivalent to this one:

    flags: ["-fsanitize=address", "-fPIC"]

Despite splitting strings as-if they were shell commands, dds does nothing else shell-like. It does not expand environment variables, nor does it expand globs and wildcards.


Specify the identity of the compiler. This option is used to infer many other facts about the toolchain. If specifying the full toolchain with the command templates, this option is not required.

Valid values are:




For LLVM/Clang


For Microsoft Visual C++

c_compiler and cxx_compiler

Names/paths of the C and C++ compilers, respectively. Defaults will be inferred from compiler_id.

c_version and cxx_version

Specify the language versions for C and C++, respectively. By default, dds will not set any language version. Using this option requires that the compiler_id be specified. Setting this value will cause the corresponding language-version flag to be passed to the compiler.

Valid c_version values are:

  • c89

  • c99

  • c11

  • c18

Valid cxx_version values are:

  • c++98

  • c++03

  • c++11

  • c++14

  • c++17

  • c++20


dds will not do any “smarts” to infer the exact option to pass to have the required effect. If you ask for c++20 from gcc 4.8, dds will simply pass -std=c++20 with no questions asked. If you need finer-grained control, use the c_flags and cxx_flags options.


Provide additional compiler flags that should be used to enable warnings. This option is stored separately from flags, as these options may be enabled/disabled separately depending on how dds is invoked.


If compiler_id is provided, a default set of warning flags will be provided when warnings are enabled.

Adding flags to this toolchain option will append flags to the basis warning flag list rather than overwrite them.

See also

Refer to base_warning_flags for more information.

flags, c_flags, and cxx_flags

Specify additional compiler options, possibly per-language.


Boolean option (true or false) to enable/disable optimizations. Default is false.


Bool or string. Default is false. If true or "embedded", generates debug information embedded in the compiled binaries. If "split", generates debug information in a separate file from the binaries.


"split" with GCC requires that the compiler support the -gsplit-dwarf option.


Select the language runtime/standard library options. Must be an object, and supports two keys:


A boolean. If true, the runtime and standard libraries will be static-linked into the generated binaries. If false, they will be dynamically linked. Default is true with MSVC, and false with GCC and Clang.


A boolean. If true, the debug versions of the runtime and standard library will be compiled and linked into the generated binaries. If false, the default libraries will be used.

On MSVC the default value depends on the top-level /debug option: If /debug is not false, then /runtime/debug defaults to true.

On GCC and Clang the default value is false.


On GNU-like compilers, static does not generate a static executable, it only statically links the runtime and standard library. To generate a static executable, the -static option should be added to link_flags.


On GNU and Clang, setting /runtime/debug to true will compile all files with the _GLIBCXX_DEBUG and _LIBCPP_DEBUG=1 preprocessor definitions set. Translation units compiled with these macros are definitively ABI-incompatible with TUs that have been compiled without these options!!

If you link to a static or dynamic library that has not been compiled with the same runtime settings, generated programs will likely crash.


Provide a command prefix that should be used on all compiler executions. e.g. ccache.


A nested object that contains advanced toolchain options. Refer to section on advanced toolchain options.

Advanced Options Reference

The options below are probably not good to tweak unless you really know what you are doing. Their values will be inferred from compiler_id.

Command Templates

Many of the below options take the form of command-line templates. These are templates from which dds will create a command-line for a subprocess, possibly by combining them together.

Each command template allows some set of placeholders. Each instance of the placeholder string will be replaced in the final command line. Refer to each respective option for more information.


Specify the way in which dds should track compilation dependencies. One of gnu, msvc, or none.


If none, then dependency tracking will be disabled entirely. This will prevent dds from tracking interdependencies of source files, and inhibits incremental compilation.

c_compile_file and cxx_compile_file

Override the command template that is used to compile source files.

This template expects three placeholders:

  • [in] is the path to the file that will be compiled.

  • [out] is the path to the object file that will be generated.

  • [flags] is the placeholder of the compilation flags. This placeholder must not be attached to any other arguments. The compilation flag argument list will be inserted in place of [flags].


    // On GNU-like compilers (GCC, Clang):
    c_compile_file:   "<compiler> -fPIC -pthread [flags] -c [in] -o[out]",
    cxx_compile_file: "<compiler> -fPIC -pthread [flags] -c [in] -o[out]",

    // On MSVC:
    c_compile_file:   "cl.exe /nologo /permissive- [flags] /c [in] /Fo[out]",
    cxx_compile_file: "cl.exe /EHsc /nologo /permissive- [flags] /c [in] /Fo[out]",


Override the command template that is used to generate static library archive files.

This template expects two placeholders:

  • [in] is the a placeholder for the list of inputs. It must not be attached to any other arguments. The list of input paths will be inserted in place of [in].

  • [out] is the placeholder for the output path for the static library archive.


    // On GNU-like:
    create_archive: "ar rcs [out] [in]",
    // On MSVC:
    create_archive: "lib /nologo /OUT:[out] [in]",

include_template and external_include_template

Override the command template for the flags to specify a header search path. external_include_template will be used to specify the include search path for a directory that is “external” (i.e. does not live within the main project).

For each directory added to the #include search path, this argument template is instantiated in the [flags] for the compilation.

This template expects only a single placeholder: [path], which will be replaced with the path to the directory to be added to the search path.

On MSVC, this defaults to /I [path]. On GNU-like, -isystem [path] is used for external_include_template and -I [path] for include_template.


Override the command template for the flags to set a preprocessor definition.

This template expects only a single placeholder: [def], which is the preprocessor macro definition argument.

On MSVC, this defaults to /D [def]. On GNU-like compilers, this is -D [def].


Supply additional flags when compiling/linking that will only be applied if standard output is an ANSI-capable terminal.

On GNU and Clang this will be -fdiagnostics-color by default.

obj_prefix, obj_suffix, archive_prefix, archive_suffix, exe_prefix, and exe_suffix

Set the filename prefixes and suffixes for object files, library archive files, and executable files, respectively.


When you compile your project and request warning flags, dds will concatenate the warning flags from this option with the flags provided by warning_flags. This option is “advanced,” because it provides a set of defaults based on the compiler_id.

On GNU-like compilers, the base warning flags are -Wall -Wextra -Wpedantic -Wconversion. On MSVC the default flag is /W4.

For example, if you set warning_flags to "-Werror" on a GNU-like compiler, the resulting command line will contain -Wall -Wextra -Wpedantic -Wconversion -Werror.