(Menu) switch statement doesnt work properly after using Serial readString

Projects Programming
1

Hi everyone! I'm new to arduino, and for my first project I wanted to build a simple serial menu. (code below)

while(!Serial.available());
char choice  = Serial.parseInt();
while(Serial.available()) Serial.read(); //get rid of CR

switch(choice) {
    case 1:
      // some code
      break;
    case 2:
    char content[1024];
    while(!Serial.available());
    String contentStr = Serial.readString();
    // some code to save contentStr  on sd card (it works);
    break;
case 3:
    // some code
    break;
case 4:
    // some code
    break;
default:
    // print invalid option
    break;
}

My problem is the following: case 2 does its job as it should, but my menu does not recognize any case below it (ex: if i press 5 i should get the invalid option message, if I press 4 the code from case 4 should execute, but I get nothing, etc.).
If i comment the line: String contentStr = Serial.readString(); in case 2 suddenly all the other cases work.
Can somebody explain to me this strange behaviour? I should mention that I use that same method of reading a string in other functions (not in a switch) and it works and I get the expected output.

2

Without knowing the rest of the code, hard to guess what's wrong. You use blocking while loops which is not a good idea. You could try to use Serial.readStringUntil('\n') instead of what you got. If you are using an AVR based MCU, the String data type may cause malfunction.

3

Which Arduino? What does the IDE say about the memory usage?

For e.g. an Uno, that is 50% of the available memory (RAM). And you will have to add that to the reported dynamic memory usage.

There are other problems; you might have to set the warning level to All in file -> preferences to see them.

C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino: In function 'void loop()':
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:23:10: warning: jump to case label [-fpermissive]
     case 3:
          ^
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:20:14: note:   crosses initialization of 'String contentStr'
       String contentStr = Serial.readString();
              ^~~~~~~~~~
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:26:10: warning: jump to case label [-fpermissive]
     case 4:
          ^
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:20:14: note:   crosses initialization of 'String contentStr'
       String contentStr = Serial.readString();
              ^~~~~~~~~~
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:29:5: warning: jump to case label [-fpermissive]
     default:
     ^~~~~~~
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:20:14: note:   crosses initialization of 'String contentStr'
       String contentStr = Serial.readString();
              ^~~~~~~~~~
C:\Users\sterretje\AppData\Local\Temp\.arduinoIDE-unsaved2022814-3948-ykhd8q.21fs\sketch_sep14a\sketch_sep14a.ino:17:12: warning: unused variable 'content' [-Wunused-variable]
       char content[1024];
            ^~~~~~~

Please provide your full sketch.

And thanks for using code-tags in your first post :+1:

4

You should not declare variables within a switch statement.

Move these statements before the switch statement OR add { } for everything in case 2:

The issue relates to variable scope.

1 Like
5

This shouldn’t compile, if there was error message post it

6

That’s ok if they are scoped

7

It does compile with warnings :wink:

8

The variable is not used so it is probably omitted by compiler so it compiles

9

To my knowledge, the compiler does not throw things away; the linker does. But I might be mistaken.

10

Because you initialize a local variable in 'case 2:' you can't reach any case after that without skipping the initialization. To fix it, either make the variable MORE local (local to case 2):

    case 2:
    {
      char content[1024];
      while(!Serial.available());
      String contentStr = Serial.readString();
      // some code to save contentStr  on sd card (it works);
    }
    break;

or don't initialize the local variable in the declaration:

    case 2:
    char content[1024];
    while(!Serial.available());
    String contentStr ;
    contentStr = Serial.readString();
    // some code to save contentStr  on sd card (it works);
    break;
11

Sorry for the late reply. Moving everything from case 2 to a new scope {} making everything 'more' local as you said fixed my bug. Thank you!

12

... as I mentioned in post #4... sigh.

13

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