A lightweight, no-frills logging library for Arduino & friends.

• simple interface - just three macros
• printf-like formatting
• each log entry is prepended by timestamp and amount of available free RAM
• automatically uses flash memory to save SRAM (if supported)
• log target can be any subclass of class Printer, e.g. class Serial
• zero memory footprint when turned off

#define ENABLE_LOG4ARDUINO
#include <log4arduino.h>

void setup() {
    Serial.begin(9600);
    LOG_INIT(&Serial);

    // use LOG() for printf-like logging
    LOG("hello, log4arduino.");
    LOG("use %s formatting: %d %c %d %c %d", "printf", 9, '+', 1, '=', 10);
    constexpr uint32_t magic = 3735928559;
    LOG("hex output: %lu == 0x%lX", magic, magic);

    // use LOGS() for simple logging of single arguments
    const char *pStr = "some string from RAM";
    LOGS(pStr);
    LOGS(F("this string is stored in flash memory"));
    LOGS(String("some String object"));
    LOGS(123);
}

void loop() { }

will print out the following on the Serial interface:

0(1623): hello, log4arduino.
0(1609): use printf formatting: 9 + 1 = 10
9(1599): hex output: 3735928559 == 0xDEADBEEF
58(1695): some string from RAM
91(1695): this string is stored in flash memory
142(1695): some String object
174(1695): 123

The actual log messages are preceeded by the current time as returned by millis() as well as the free heap space, e.g. 91(1695):.

In the main menu of the Arduino IDE, select Sketch > Include Library > Manage Libraries... and search for log4arduino, then press install.

Add log4arduino to your library dependencies in your platformio.ini project file, e.g.

...
[env:nanoatmega328]
platform = atmelavr
board = nanoatmega328
framework = arduino
lib_deps=log4arduino
build_flags=-DENABLE_LOG4ARDUINO
...

With the build_flags option, you can enable/disable log4arduino at build time.

To use log4arduino, define ENABLE_LOG4ARDUINO and include the log4arduino.h header. If ENABLE_LOG4ARDUINO is not defined, then logging will be disabled (and not compiled in). This is what you typically want in a release build.

3 Macros are used for logging: LOG_INIT, LOG and LOGS:

The LOG_INIT(target) macro initializes the logging. It takes a pointer to a subclass of the Print class as argument, which specifies the log target, e.g. LOG_INIT(&Serial). No logging will happen until LOG_INIT is called. If needed, call LOG_INIT(nullptr) to turn off logging during runtime.

Use the LOG(fmt, ...) macro to log in a printf-like fashion. The fmt format string will automatically be stored in flash memory using the F() macro to reduce amount of SRAM being used.

Use the LOGS(s) (the S stands for simple) macro, to directly log out the given value using the log target's print method.

log4arduino does not support log levels. This lib is not meant for enterprise development and we have to keep the memory footprint low. YAGNI.

Jan Delgado

MIT