I have written my own 'assert' since I want to use it for both Windows and Arduino. The class is called from many files (about 10).


#pragma once

#define assert(expr) AssertUtils::Assert2((expr), (__func__), (__FILE__), (__LINE__));

class AssertUtils
    static void Assert2(bool expression, const char* funcName, const char* fileName, int line);


#include "AssertUtils.h"
#include "Arduino.h"

/* static */ void AssertUtils::Assert2(bool expression, const char* funcName, const char* fileName, int line)
    if (!expression)
        Serial.println(line, DEC);

        // Abort program execution.

When I compile this, the SRAM usage is 1469 bytes (together with the rest of my sketch and classes).

When I comment the line below, I get a segmentation fault in a random assert call (when I comment out that call, I get it in the next, etc.).


When I also comment out the second print statement, the compiler reports only 1137 bytes SRAM usage (which I expect since this was about equal until before I added the Assert class).



  1. How can I get rid of the segmentation fault?
  2. How can it be that about 332 bytes are used for one two additional print statements? (maybe related to the const char* buffering (?)
  • 1
    the segmentation fault is a bug in compiler in 1.6.22 and 1.6.23. more here forum.arduino.cc/index.php?topic=619213.msg4195749#msg4195749
    – Juraj
    Jun 2, 2019 at 16:00
  • 1
    try F(__FILE__) and F(__func__). (change the parameter type to __FlashStringHelper)
    – Juraj
    Jun 2, 2019 at 16:03
  • 1
    @Juraj Somehow it only works for __FILE__ but not for __func__. Anyway using F( __FILE__) was about -90B difference (It's probably full path and it was only used in one file).
    – KIIV
    Jun 2, 2019 at 16:32
  • 1
    so the compiler optimizes the parameters away if hey are not used
    – Juraj
    Jun 2, 2019 at 17:49
  • 1
    Why are you wasting a class on this? Just use the prints directly in the macro.
    – Majenko
    Jun 2, 2019 at 18:48

1 Answer 1


Note, this answer is not MY answer, but approximately the combination of the first 5 comments from my original question.

What I did was:

  • (Juraj) Changed the compiler version to 6.21
  • (juraj) Added an F in F(__FILE__)
  • (KIIV) Removed func; this did not work with the F flash helper, but I can find back the code anyway unambiguously because of the file name + line number.
  • (Majenko) I removed the class and use a macro. This costs some more Flash memory (depending on the number of asserts I use, but I'm still around 40% (was 35%).

The SRAM usage is now 1125 bytes, even less than where I'm started with.

The resulting code is below:

#define assert(expression) \
  if (!(expression)) \
  { \
    Serial.println(F(__FILE__)); \
    Serial.println(__LINE__, DEC); \
    Serial.flush(); \
    abort(); \
  • 1
    About class - in this case it was used as old form of namespaces (as namespaces weren't present in c++ until 1990). However struct was used more likely as it doesn't need public: specifier.
    – KIIV
    Jun 2, 2019 at 20:46

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