Mixed structure with int and string

Question

I want to create a structure like this:

 struct commands
{
  int   cmd;
  char  descr[25];
};

commands cmds[] =
{
  {16, "Hammond Organ"},
  {17, "Percussive Organ"},
  {18, "Rock Organ"},
  { 0, "" }                   // end of list marker 
};

The compiler doesn't protest, but in a simulator the values of cmds[i].descr are all zeros.

And the line

Serial.write(cmds[1].descr);

prints nothing.

Please recommend how to rewrite the code.

Thanks.

EDIT

Thanks for your answer. It helped me a lot.

There is something wrong with the simulator (Simulator for Arduino - version 1.11E Designed by Virtronics). In the meantime I received the Mega 2560 board and the code works well with the board.

What version of the IDE and avr-g++ are you using? If you enable verbose compilation, you should see the location of the avr-tools (avr-g++, avr-objdump...) and the generated elf file. Run avr-nm -Cn path_to_the_elf_file to see the memory address where cmds is stored, then avr-objdump -s -j .data path_to_the_elf_file to see its contents. Does it look as expected? — Edgar Bonet
– Edgar Bonet, Commented Dec 23, 2019 at 10:15
Arduino IDE 1.8.10. As I am a beginner, I don't understand the rest of your question. — bernkopf48
– bernkopf48, Commented Dec 23, 2019 at 20:27
My issue is now resolved by the answers of VillageTech and VE7JRO. — bernkopf48
– bernkopf48, Commented Dec 23, 2019 at 20:33

VE7JRO · Accepted Answer · 2019-12-23 01:20:51Z

2

There must be something wrong with the simulator you're using, because your code works for me (Arduino IDE 1.8.9, OSX, Arduino Uno).

struct commands
{
  int   cmd;
  char  descr[25];
};

commands cmds[] =
{
  {16, "Hammond Organ"},
  {17, "Percussive Organ"},
  {18, "Rock Organ"},
  { 0, "" }                   // end of list marker 
};

void setup(){
  Serial.begin(9600);
  Serial.write(cmds[1].descr);
}

void loop(){}

answered Dec 23, 2019 at 1:20

VE7JRO

2,51419 gold badges28 silver badges31 bronze badges

The above sketch produces no errors or warnings using my OS and IDE version.

VE7JRO
– VE7JRO

2019-12-23 01:24:31 +00:00
Commented Dec 23, 2019 at 1:24
1

Same here. Compiles cleanly with -Os -Wall -Wextra and works perfectly with both avr-g++ 5.4.0 (shipped with Ubuntu 19.10) and 7.3.0 (shipped with the Arduino IDE 1.8.10).

Edgar Bonet
– Edgar Bonet

2019-12-23 09:53:10 +00:00
Commented Dec 23, 2019 at 9:53

Add a comment |

bernkopf48 · Accepted Answer · 2019-12-23 20:21:26Z

Try to use char pointer notation (char *) instead of array notation (char[]) in structure declaration:

struct commands
{
    int   cmd;
    char*  descr;
};

OR -

use struct declaration as-is, but change the array initialization like below:

commands cmds[] =
{
    {16, {"Hammond Organ"}},
    {17, {"Percussive Organ"}},
    {18, {"Rock Organ"}},
    { 0, {""}}                   // end of list marker 
};

Additionally, it seems that it always should be written as:

struct commands cmds[] = 
{
    // here your code
};

If you have disabled warnings in your compiler, enable them again - and try to write program the way that you will newer receive warnings.

Thanks for your answer. It helped me a lot.

There must be something wrong with the simulator (Simulator for Arduino - version 1.11E Designed by Virtronics). In the meantime I received the Mega 2560 board and both char pointer notation (char ) and array notation (char[]) work well with the board. The compiler (Arduino IDE v. 1.8.10) really produces warnings: ISO C++ forbids converting a string constant to 'char' [-Wwrite-strings]. Perhaps the simulator is more meticulous than the compiler and therefore refuses to work with a code thar generates warnings.

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