Updated String library to use C++11 iterators.

[Chris--A]

This will allow using the String library in a ranged for loop. Also the additions expose the first and last character pointers, which may be of use somewhere.

void setup() {

  Serial.begin( 9600 );
  String s = "Hi, this is a test of C++11 iterators.";

  for( char c : s ){
    Serial.print( "Character in string: " );
    Serial.println( c );
  }
}
void loop(){}

This modification is placed inside the check for C++11 which is also due for update here: matthijskooijman@6624d61

[Chris--A]

I wanted to have the begin and end function return types based of the c_str function, however it seems not possible due to String being incomplete at this point in code.

auto end() -> decltype( ((String*)nullptr)->c_str() ) { return c_str() + length(); }

However I left it in to clearly show that it is a C++11 feature ( new declaration syntax ). I chose this because many Arduino libs have begin() as a method to delay construction and avoid the static initialization order problems, however this begin has quite a different meaning.

What do you think is best? maybe a comment above the lines showing that they are intended for ranged loops, and not construction/initialization of something.

[Chris--A]

As C++98 code does use begin and end for stl iterators, and because the dependency for c_str() is not possible, I have re-written them into functions usable by both 98 and 11 standards.

[matthijskooijman]

Sounds good.

[Chris--A]

This update does not need to wait until C++11 is turned on.

It can be of use now, just like STL containers:

for( char *ptr = s.begin() ; ptr != s.end() ; *ptr++ = /* modify each character in string */ );

It might be worth noting if documented, that end() returns the null pointer, so the loop above and a C++11 ranged loop do not include the null in the iteration.

[Chris--A]

Now that C++11 has been enabled, can this be merged too!

[cmaglie]

Rebased and merged, thanks @Chris--A !