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I am trying to run the test program from Adafruit, with their libraries, for an Arduino controlling a Nokia5110 display and get this error message:

Arduino: 1.5.8 (Linux), Board: "Arduino Pro or Pro Mini, ATmega328 (5V, 16 MHz)"

    /home/Harry/Arduino/libraries/Adafruit_GFX/glcdfont.c:9:23: error: variable 'font' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
     static unsigned char  font[] PROGMEM = {
                           ^
    Error compiling.

Please can anyone explain this? I can happily give more details, but I am not yet sure how much is needed and the files are rather too long to include them all at this stage.

  • Include you FULL code. – Dat Ha Dec 22 '16 at 18:08
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    Looks like this was already fixed. Are you using an old GFX library? – gre_gor Dec 22 '16 at 18:15
  • The error already says what you should do, and even points to were you need to add it. – Gerben Dec 22 '16 at 19:48
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The problem is you're using an old version of the Adafruit GFX Library, which was written for a previous version of the Arduino IDE. You just need to install the latest version of the library and your problem will be solved:

  1. Download https://github.com/adafruit/Adafruit-GFX-Library/archive/master.zip
  2. Unzip the downloaded file.
  3. Rename the unzipped folder Adafruit_GFX
  4. Replace /home/Harry/Arduino/libraries/Adafruit_GFX with the folder.

If you run into any other problems after doing that I recommend trying the latest version of the Arduino IDE. The version you're using is very outdated.

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You can not change variables in PROGMEM memory.
Therefore the variable must be a const variable.
This way the compiler can check whether you try to change the value or not.

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