PROGMEM/F: section type conflict with __c

[bertmelis]

I haven't got enough understanding of the inner working to assert if this is a coding error, or a bug, but I've got the following:

sketch:

#include "TestClass.h"

TestClass testClass;
const uint32_t INTERVAL = 5000;

void setup() {
  Serial.begin(115200);
  testClass.setPrinter(&Serial);
}

void loop() {
  static uint32_t previousMillis = 0;
  if ((millis() - previousMillis) > INTERVAL) {
    previousMillis = millis();
    testClass.doSomething();
  }
}

TestClass.h:

#pragma once
#include <Arduino.h>


class TestClass {
  public:
    void setPrinter(HardwareSerial* serial);
    void doSomething();
  private:
    static const char* _testString;
    HardwareSerial* _serial;
};

TestClass.cpp:

#include "TestClass.h"

const char* TestClass::_testString PROGMEM = "Test String";

void TestClass::setPrinter(HardwareSerial* serial){
  _serial = serial;
}

void TestClass::doSomething() {
  //do something
  _serial->println(F("testing"));
}

Compiling results in an error: TestClass.cpp:3: error: TestClass::_testString causes a section type conflict with __c

Removing the F macro solved the error as does removing the PROGMEM modifier. However, I'd like to use both. eg: list of error messages and printing small debug messages, both from progmem.

[bertmelis]

OK, it obviously had nothing to do with being is a class (and so being in a seperate file). You just cannot use PROGMEM and F() in the same file. as in this sketch:

const uint32_t INTERVAL = 5000;
const char* testString PROGMEM = "Testing 1 ";

// Print a string from Program Memory directly to save RAM 
void printProgStr (HardwareSerial* serial, const char* str)
{
  char c;
  if (!str) 
    return;
  while ((c = pgm_read_byte(str++)))
    serial->print(c);
}

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

void loop() {
  static uint32_t previousMillis = 0;
  if ((millis() - previousMillis) > INTERVAL) {
    previousMillis = millis();
    printProgStr(&Serial, testString);
    Serial.println(F("Testing_F"));
  }
}

[Makuna]

Please see #3369 for a possible solution.

[devyte]

@bertmelis did you test the solution found in #3369?

[bertmelis]

Or I just don't understand the solution, or it doesn't solve my "error".

I'm trying to put debug messages in PROGMEM using an array of char pointers, as in Nick Gammon's blogpost. These debug messages are used in a class-library, for now without any namespace defined. I had all the declarations and initialisations in a header file.

[Makuna]

While the declaration can be, the initializations can't be in the header; as mentioned in #3369.

[bertmelis]

But then also: I've got a class method with Serial.println(F("debug text"));. This works untill I inline the method. Despite the proposed solution, it is quite unhandy.

But I'll ask it in another way: are there any thoughts on improving the issue? Or shall I live with it?

(in case of the latter, I'll modify my code to deal with it and close the issue)

[Makuna]

You can move the actual string into a const variable that is declared in the header, leaving the Serial.println in place.

This is really what you would want anyhow.

Currently, anything in a F("") will be a duplicated string, even if the text is the same. For any work other than simple examples and sketches, you really want a separate .h/.cpp that contain all your strings.

[devyte]

Closing due to user error.