How can I get the source files for Arduino libraries?

Question

I've been looking for a while inside Arduino's files to find the core library. However, I haven't found them yet. Where on my hard drive can I obtain the core library files (.cpp and .h) necessary for all Arduino code?

Looking around on Google, I couldn't find a way to find the above files. I did see something about getting an .a file while Arduino is compiling, however, that isn't what I want. I want to browse the code and look at functions such as delay to see how they would react when given the values not expected. (i.e. Will my code stall if I use delay(-200); by not being to exit the loop, or will it create a black hole and disrupt the space-time continuum?)

• bobzic: I was interested in the question, but what I want is the source code for strcpy and strcat in assembler source code. I downloaded the Master Library but I cannot locate anything remotely similar to strcpy or strcat. OR Maybe I cannot see the wood for the trees?
• Anonymous Penguin: @bobzic I suggest that you ask another question specifying which files you want to find.

Answer 1

The base Arduino source files are in the Arduino installation, under cores/arduino/. Source for additional libraries included are in libraries/.

• jippie: And don't forget /usr/lib/avr/include/ or whatever that translates to on non-Linux systems.
• Tomáš Zato: Too bad I installed it as Windows 10 app and cannot access the installation folder.
• Thomas Weller: This information seems outdated. The libraries folder is empty now and hardware has moved

Answer 2

The code is also available online for those times you don't have the IDE installed:

https://github.com/arduino/Arduino

• Tomáš Zato: Can't find the header files there.
• JBaczuk: see my answer below: arduino.stackexchange.com/a/68658/59512

Answer 3

On a Mac, the path to the source code folder is:
Arduino.app/Contents/Resources/Java/Hardware/Arduino/Cores/Arduino. I'd expect it would be the same from /Java/ on down in other OSes.

Path to library sources (Arduino-Mac)

Answer 4

The arduino source files can be found on Github at https://github.com/arduino/Arduino, however the libraries have been moved to their own repositories:

• https://github.com/arduino/ArduinoCore-avr
• https://github.com/arduino/ArduinoCore-sam
• https://github.com/arduino/ArduinoCore-samd

Answer 5

There are multiple places where you can look. As at IDE 1.6.4 (Ubuntu version) some are in:

(install location)/libraries

But these are the high-level libraries, in particular:

Bridge
Esplora
Ethernet
Firmata
GSM
LiquidCrystal
Robot_Control
RobotIRremote
Robot_Motor
SD
Servo
SpacebrewYun
Stepper
Temboo
TFT
WiFi

---

That does not cover the low-level libraries like Tone, Print, main, etc. These are in:

(install location)/hardware/arduino/avr/cores/arduino

There you would find the Arduino core libraries like:

abi.cpp
Arduino.h
binary.h
CDC.cpp
Client.h
HardwareSerial0.cpp
HardwareSerial1.cpp
HardwareSerial2.cpp
HardwareSerial3.cpp
HardwareSerial.cpp
HardwareSerial.h
HardwareSerial_private.h
HID.cpp
hooks.c
IPAddress.cpp
IPAddress.h
main.cpp
new.cpp
new.h
Printable.h
Print.cpp
Print.h
Server.h
Stream.cpp
Stream.h
Tone.cpp
Udp.h
USBAPI.h
USBCore.cpp
USBCore.h
USBDesc.h
WCharacter.h
WInterrupts.c
wiring_analog.c
wiring.c
wiring_digital.c
wiring_private.h
wiring_pulse.c
wiring_shift.c
WMath.cpp
WString.cpp
WString.h

---

However even that does not locate things like strcpy. The header files for them can be found at:

(install location)/hardware/tools/avr/avr/include/

There you will find:

alloca.h
assert.h
ctype.h
errno.h
inttypes.h
math.h
setjmp.h
stdfix-avrlibc.h
stdint.h
stdio.h
stdlib.h
string.h

---

Even that is not the full story. In a subdirectory (avr) you will find the avr-related things, with files for different processors, such as (in part):

boot.h
builtins.h
common.h
cpufunc.h
crc16.h
delay.h
eeprom.h
fuse.h
interrupt.h
io1200.h
io2313.h
...
iox64d4.h
iox8e5.h
lock.h
parity.h
pgmspace.h
portpins.h
power.h
sfr_defs.h
signal.h
signature.h
sleep.h
version.h
wdt.h
xmega.h

---

As for the source of strcpy, I don't think it is in the distribution. They include the standard libraries, pre-compiled. For example, if you look in:

(install location)/hardware/tools/avr/avr/lib

You will see various pre-compiled libraries, for example:

libc.a
libm.a
libprintf_flt.a
libprintf_min.a
libscanf_flt.a
libscanf_min.a

To find the source you would need to find where the AVR source of libc is (possibly at http://www.nongnu.org/avr-libc/).

---

As for the Mac, all this stuff is a few levels down in the "Application Package" which you can view by right-clicking and selecting "Show Package Contents". Look in the Contents/Resources/Java folder.

---

None of these places are where you should put your own libraries (ones you write or download). They should go into the libraries folder which is a subdirectory of your sketchbook folder. Create the libraries folder if it does not exist. That way user-installed libraries persist from one version of the IDE to the next.

Answer 6

I think this may have changed in newer versions. On my Mac Big Sur, Arduino 1.8.15 they are here: /Applications/Arduino.app/Contents/Java/libraries