Why is this not an error?

Projects Programming
1

For your consideration:

 for (int i = 0; i < maxLength; i++); {
      dest[i] = char(EEPROM.read(startAdr + i));
    }

It took me a while to find the error, but why didn't the IDE see it as an error or at least a warning?

3

Or the bracket at the end of the first line? Guessing that was a typo when posting and Delta_G is on the right track.

Edit: once again, not reading thoroughly bit me. Delta_G already mentioned the bracket.

4

I have a question about this.
Wouldn't the i inside the brackets be out of scope?

5

The i will only ever be a number between 0 and whatever maxlength is set to.

7

Delta_G:
Maybe there is another i.

That's a big existential question now, isn't?

8

There must be another 'i'. Global or local.

#include <EEPROM.h>
const int maxLength = 10;
char dest[maxLength];
int startAdr = 5;


void setup()
{  
  for (int i = 0; i < maxLength; i++)
    ;
  {
    dest[i] = char(EEPROM.read(startAdr + i));
  }
}


void loop() {}

sketch_aug13a/sketch_aug13a.ino: In function 'void setup()':
sketch_aug13a:11:10: error: 'i' was not declared in this scope
     dest[i] = char(EEPROM.read(startAdr + i));
          ^
exit status 1
'i' was not declared in this scope
9

Delta_G:
No he's right. It should be out of scope on that next line. It only exists in the for loop. But we can't see anymore of the code. Maybe there is another i.

Oops- bad example.
Yes, i was out of scope as I created the example. In the actual code I was not using the iterative inside the brackets.

Nevermind!

11

I've never ran into that particular out of scope issue. But I now know what to look for in the future. Still much to learn, me thinks.

13

That's what I gathered from the replies that followed. delta[] tries to take it outside the for loop. Which it can't.

15

It would be nice if the compiler threw a warning for an if(), while() or for() loop with a semicolon followed by a block, as that is almost always a mistake. But it doesn't.

16

DrAzzy:
It would be nice if the compiler threw a warning for an if(), while() or for() loop with a semicolon followed by a block, as that is almost always a mistake. But it doesn't.

GCC 7.3.0 does give you a warning:

test_for.cpp:9:4: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
    for (int i = 0; i < maxLength; i++);
    ^~~
test_for.cpp:10:4: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
    {
    ^
18

Ok Delta_G. I think, keyword think, I see what you're saying. The use of ; in that location pretty much terminates the for statement. Just like it terminates most other statements. Therefore, the bracketed i was not declared. Nor the one later on.

20

Shouldn't be allowed to use "i" as an array index anyway, since then when someone forgets code tags, it get italicised :wink:

dest = char(EEPROM.read(startAdr + i));

21

DangerToMyself:
The use of ; in that location pretty much terminates the for statement. Just like it terminates most other statements. Therefore, the bracketed i was not declared. Nor the one later on.

The 'if' statement can only contain one statement:

if ( <expression> ) <statement> [else <statement>]

Note the "else part is optional.
The ';' is a valid statement so it completes (not terminates) the 'if' statement. Another valid statement is a block statement:

{ <statement> <statement>... }

So you can write:

  if ( <expression> )
  {
    <statement>
    <statement>
  }
  [else
  {
  <statement>
  <statement>
  }]

In all cases, the "if ( )" is followed by a single "statement" which is optionally followed by an "else" and another single statement.