How to get rid of "undefined reference to 'Class::member'"? in conjunction with initialization of an array

Question

When building my code I get the following "undefined reference"-errors, which I cannot get rid of. I've already tried several hints from stack overflow but nothing helps :-(. Maybe you have an idea?

I use VSCode with PlatformIO for an Arduino Uno on Mac OS.

in function `get7SegBitMap':

/Users/christian/Projekt/src/charmap7seg.cpp:70: undefined reference to 'Led7SegmentCharMap::bitMap'
/Users/christian/Projekt/src/charmap7seg.cpp:70: undefined reference to `Led7SegmentCharMap::bitMap' collect2: error: ld returned 1 exit status

The hierarchy is:

main.cpp includes ledmatrix.hpp
- ledmatrix.cpp includes ledmatrix.hpp
- ledmatrix.hpp includes charmap7seg.hpp
  - charmap7seg.cpp includes charmap7seg.hpp

charmap7seg.hpp

#pragma once
#include <Arduino.h>

class Led7SegmentCharMap {
private:
    static const uint8_t bitMap[];  // will be initialized in cpp-file
    uint8_t getCharMapIndex(const unsigned char outChar);
public:
    // Konstruktur
    Led7SegmentCharMap();
    // BitMap zur Darstellung auf der 7-Segment-Anzeige für outChar ermitteln
    uint8_t get7SegBitMap(const unsigned char outChar);
};


int set7SegValue(const LedMatrixPos pos, const uint8_t charBitMap);

charmap7seg.cpp

#include <Arduino.h>
#include <charmap7seg.hpp>

// Konstruktur
Led7SegmentCharMap::Led7SegmentCharMap() {
    uint8_t bitMap[] = {    ///< charMap contains bitmaps for 7-seg-displays
        //gfedcba
        0b0111111, ///<  "0": Segments f, e, d, c, b, a   --> bitMap[0]
        0b0000110, ///<  "1": Segments c, b               --> bitMap[1]
        0b1011011, ///<  "2": Segments g, e, d, b, a      --> bitMap[2]
        (...)
    }
    (void)bitMap; // to suppress the compiler warning "unused variable"
};


uint8_t Led7SegmentCharMap::get7SegBitMap(const unsigned char outChar) {
    return bitMap[getCharMapIndex(outChar)];  //                 <===== this is line 70
};

(...)

ledmatrix.hpp

#pragma once
#include <Arduino.h>
#include <charmap7seg.hpp>

class LedMatrix {
private:
    Led7SegmentCharMap charMap;
    (...)
public:
    Led7SegmentCharMap();  // Konstruktor
    uint8_t get7SegBitMap(const unsigned char outChar);
    void LedMatrix::display(const String outString);
    (...)

ledmatrix.cpp

#include <ledmatrix.hpp>
(...)
void LedMatrix::display(const String outString) {
    (...) // get a char out of outString --> outChar
    uint8_t charBitMap = charMap.get7SegBitMap(outChar); // get 7-seg-"bitmap"
    (...)
};
(...)

My expection is that all dependencies are fulfilled (which is not true regarding the error messages). I had some trouble with initializing the bitMap-array. Maybe the undefined reference error is related to that?

`// to suppress the compiler warning "unused variable"` You misspelled "I have no idea what I'm doing here". Please read [this](https://stackoverflow.com/questions/19349566/c-cannot-initialize-static-data-member). — n. m. could be an AI, Dec 03 '22 at 23:43
yes, you are right. I am still learning and trying to understand :-). I've read it, but I do not understand :-( — CHarraeus, Dec 04 '22 at 08:42
ok, what I understand: in charmap7seg.cpp the line **uint8_t bitMap[] = {** ist wrong, because it defines a new variable (local to the contractor). So it does not initialize the bitMap declared in the .hpp file. — CHarraeus, Dec 04 '22 at 08:54
right, you need to define bitMap separately at the file level in one .cpp file. — n. m. could be an AI, Dec 04 '22 at 15:37

CHarraeus · Accepted Answer · 2022-12-07T11:34:30.107

Today I found a hint here: here.

With this I've got a compilable solution. In the cpp file it is necessary to move the bitMap declaration out of the constructor and do the initialization there. See new cpp file below.

So the initial question

How to get rid of "undefined reference to 'Class::member'"? in conjunction with initialization of an array

was wrong and should be:

How to declare an c-array in header file and define it in the cpp-file without specifying the size/dimension?

charmap7seg.hpp

class Led7SegmentCharMap {
public:
    uint8_t get7SegBitMap(const unsigned char outChar);

private:
    static const uint8_t bitMap[];      ///< Bitmap-Tabelle mit den Bitmustern
};

charmap7seg.cpp

const uint8_t Led7SegmentCharMap::bitMap[] =  {    ///< charMap contains bitmaps for 7-seg-displays
                            ///< bzw. den Buchstaben darstellen.
        0b0111111, ///<  "0": Segmente f, e, d, c, b, a    --> bitMap[0]
        0b0000110, ///<  "1": Segmente c, b                --> bitMap[1]
        0b1011011, ///<  "2": Segmente g, e, d, b, a       --> bitMap[2]
};

(...)

Corrected code for charmap7seg.hpp and .cpp to show how to make `Led7SegmentCharMap::bitMap` private. The question "How to declare an c-array in header file and define it in the cpp-file without specifying the size/dimension?" is now answered and solved. — CHarraeus, Dec 07 '22 at 11:34

score -1 · Answer 2 · answered Dec 03 '22 at 23:40

erase the uint8_t. you are redeclaring the bitmap and it's going out of scope when the constructor ends. instead do:

this->bitMap[] = {    ///< charMap contains bitmaps for 7-seg-displays
        //gfedcba
        0b0111111, ///<  "0": Segments f, e, d, c, b, a   --> bitMap[0]
        0b0000110, ///<  "1": Segments c, b               --> bitMap[1]
        0b1011011, ///<  "2": Segments g, e, d, b, a      --> bitMap[2]
        (...)
    }

This will not solve the problem. – n. m. could be an AI Dec 03 '22 at 23:43 — n. m. could be an AI, Dec 03 '22 at 23:43

How to get rid of "undefined reference to 'Class::member'"? in conjunction with initialization of an array

2 Answers2