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Arduino Sketch preprocessor

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This repository contains the source code of the Arduino Sketch preprocessor. The main purpose of this tool is to parse an Arduino Sketch (usually made with the Arduino IDE) and convert it into a valid C++ source code.

This tool is based on the Clang/LLVM C++11 parser and provides also some useful features used in the Arduino IDE like:

  • Diagnostics output in JSON format
  • Code autocomplete suggestions output in JSON format

About the Arduino Sketch (.ino) preprocessing

The Arduino Sketch is a simplified C++ source code that can be composed by many files with the extension .ino. To convert the Sketch into a valid C++ file, a number of actions are needed:

  • If the Sketch is composed by many .ino files, those files are concatenated together into a single .ino.cpp file
  • An #include <Arduino.h> is added at the beginning of the Sketch if not already present
  • All needed libraries are detected and include paths are discovered
  • All #include directives are replaced with the actual content of the files included (this is made with a run of gcc or another command line compatible compiler with the -E flag)

and finally:

  • The resulting file is preprocessed to automatically add missing function prototypes (forward declarations)

The arduino-preprocessor tool takes care to handle this last step.


./arduino-preprocessor [-output-only-needed-prototypes]
                       [-help] [-version]
                       <sketch.ino.cpp> --
                       [extra compiler options]

The only mandatory parameter is the name of the file to be processed and the terminating double dash --. Every parameter after the -- is passed as-is to the clang compiler backend.

The tool outputs the processed source code on the standard output.

For example the file t.cpp:

void a() {

void b() {

will be processed as:

$ ./arduino-preprocessor t.cpp --
#line 2 "/home/cmaglie/Workspace/arduino-preprocessor/t.cpp"
void a();
#line 6 "/home/cmaglie/Workspace/arduino-preprocessor/t.cpp"
void b();
#line 2 "/home/cmaglie/Workspace/arduino-preprocessor/t.cpp"
void a() {

void b() {

Option -output-only-needed-prototypes

Note: this option is very experimental and barely tested, use at your own risk.

By default arduino-preprocessor produces the forward prototypes of all functions, but if the option -output-only-needed-prototypes is used, the output will contains only the needed prototypes. If we look at the previous example the result will be:

$ ./arduino-preprocessor t.cpp -output-only-needed-prototypes --

#line 6 "/home/cmaglie/Workspace/arduino-preprocessor/t.cpp"
void b();
#line 2 "/home/cmaglie/Workspace/arduino-preprocessor/t.cpp"
void a() {

void b() {

Option -output-code-completions=file:line:col

Output code completions for the specified file at the specified line in JSON format. file should be specified with full path (as reported in the #line directives of the processed output).

line and col are 1-based indexes (so the first column/line is 1 and not 0)


$ ./arduino-preprocessor t.cpp -output-code-completions=/home/cmaglie/Workspace/arduino-preprocessor/t.cpp:3:1 --
[...big json output follows...]

The processed source will not be part of the output when this option is enabled.

Option -output-diagnostics

Output diagnostics (errors and warnings) in JSON format. The processed source will not be part of the output if this option is enabled.

Option -debug

This option enable debugging output during the processing of the Sketch and a lot of debugging messages are printed. This option should be used when a problem is found to understand what's happening and to produce a better bug-report when filing an issue.

Option -version

Prints the version of the tool

Option -help

Prints a short help


This tool use code from the following projects:


Parses an Arduino Sketch and converts it into valid C++ source code


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