The problems in my face but, my head is in space

Projects General Guidance
1

Hi Guys,

I had this code working earlier but, somehow I changed something. I trimmed the code back all the way to the very basics.

int len = 14;
char data[len];
void setup() {}
void loop() {}

The sketch compile error is:

sketch_jan13a:3:14: error: array bound is not an integer constant before ']' token
 char data[len];
              ^
exit status 1
array bound is not an integer constant before ']' token

The problem is obvious to someone but, I don't get it. I read this post from a year ago and I don't get it. Thanks for any insight.

2

The error message is clear. Try this

const int len = 14;
char data[len];
3

Thank you. That worked. I almost tried that but, I felt that I should understand the compile error that I was getting. "not an integer constant" just wasn't clear enough for me I guess.

The prior code in a nut shell was:

byte len = whatIsWritten.length(); 
// some code
char data[len+1];

The above works without 'const'. Anyway, problem solved. Thank you very much.

4

I doubt that. Local array variables can be temporarily defined like that, valid ONLY within a function or block, but not for the main program.

5

That's why. Thank you.

6

It's because the compiler allocates fixed memory areas for arrays at compile time. If the size of the array is a variable, how could it do that? Either

  1. Changing the value of the variable would violate that principle if it is used to specify the array size, risking accesses outside of the array bounds
    or
  2. Allowing arrays to change size dynamically would dramatically complicate the allocation of memory (but in C++ STL those kinds of arrays do exist).
7

And even that is dodgy, i.e., not allowed in ISO C++.