Arduino Printf

This library adds support for the printf() function to Arduino projects. This code leverages the embeddedartistry/printf library (a fork of eyalroz/printf, which is designed for use in embedded systems. For more information about what is available, please refer to the parent library documentation.

What This Library Provides

This library provides a standalone implementation for the following functions:

• printf()
• sprintf() and snprintf()
• vprintf() and vsnprintf()

Project Target

This library aims to offer a complete printf() solution while maintaining low storage and RAM requirements. This is critical for MCUs with limited storage and RAM. This project is ideal for AVR based MCUs like the Arduino Uno and it's siblings.

ESP8266 and ESP32

The Arduino implementations for the ESP8266 and ESP32 already include a printf() implementation as part of the base library. You do not need this library for those platforms.

Using the Library

To use this library in your Arduino project, you need to include the header:

#include <LibPrintf.h>

void setup() {
    Serial.begin(115200);
}

By default, the library can be used without any special initialization. Any printf() calls will be output using the Arduino Serial interface. If you need to use a different interface, call printf_init.

If you only want to use s[n]printf, then you do not need to initialize the library.

Advanced Usage

See advanced_usage.md.

Configuration

If memory footprint is critical, you can disable library features using compiler definitions. Available controls are:

• PRINTF_DISABLE_ALL
  • Remove all printf calls from the program
• PRINTF_NTOA_BUFFER_SIZE (unsigned integer)
  • 'ntoa' conversion buffer size, this must be big enough to hold one converted numeric number including padded zeros (dynamically created on stack)
  • Default: 32 bytes
• PRINTF_FTOA_BUFFER_SIZE (unsigned integer)
  • 'ftoa' conversion buffer size, this must be big enough to hold one converted float number including padded zeros (dynamically created on stack)
  • Default: 32 bytes
• PRINTF_DISABLE_SUPPORT_FLOAT
  • support for the floating point type (%f)
• PRINTF_DISABLE_SUPPORT_EXPONENTIAL
  • support for exponential floating point notation (%e/%g)
  • Default: active
• PRINTF_DEFAULT_FLOAT_PRECISION (unsigned integer)
• PRINTF_MAX_FLOAT (float value)
  • define the largest float suitable to print with %f
  • Default: active
  • 1e9
• PRINTF_DISABLE_SUPPORT_LONG_LONG
  • support for the long long types (%llu or %p)
  • Default: active
• PRINTF_DISABLE_SUPPORT_PTRDIFF_T
  • support for the ptrdiff_t type (%t)
  • Default: active

For AVR chips, the library will automatically set PRINTF_DISABLE_SUPPORT_EXPONENTIAL and PRINTF_DISABLE_SUPPORT_LONG_LONG. You can re-enable these settings by defining PRINTF_PREVENT_DEFAULT_AVR_SETTINGS.

Because these settings control behavior in the source file, they cannot be defined in the sketch. You must adjust the compilation commands for your project in order for the changes to take effect.

If you're using a Makefile or other build system, you'd use the -D flag (e.g., -DPRINTF_DISABLE_SUPPORT_EXPONENTIAL) to the library build target. For Arduino IDE, the flags need to be added to the compiler.extra_flags property in platform.txt or platform.local.txt. You would need to restart the IDE for the changes to take effect.

Here are comparisons for a simple test sketch showing the overall sketch size for different configurations:

Examples

Multiple examples are provided with this library in the examples/ folder.

• Default Usage
  • Without any initialization, Serial will be the default output for printf()
  • This example initializes the Serial class and prints in a loop
• Specify Print Class
  • Any class derived from the Print base class can be used with the Arduino Printf library
  • This example initializes printf with Serial1 instead of Serial
• Override Putchar
  • This example overrides putchar_() and adds a space in between every letter
  • You can implement any kind of logic within putchar_() that you like, such as outputting information to multiple ports