Detecting errors in String operations

[BojanJurca]

Hello,

If a String creation fails it is possible to detect this error in the code, like:

String s = "abc";
if (!s) ... // error, out of heap or something ...

However the error detection doesn't work with String expressions:

#define howLarge 5000
String *strArray = new String [howLarge]; 

void wasteAlmostAllMemory () {
  for (int i = 0; i < howLarge; i++) strArray [i] = " wasted memory ";
  while (true)
    for (int i = 0; i < howLarge; i++)
      if (!strArray [i].concat (" more wasted memory "))
        return;
} 

String returnLongString () {
  return "This is a long string, much longer than fits into free memory, although not right now.";
}

void setup () {
    Serial.begin (115200);

    String longString = returnLongString ();

    Serial.printf ("Wasting memory, please wait ... ");
    wasteAlmostAllMemory ();
    Serial.printf ("memory successfuly wasted\n");

    String resultString;

    // 1.
      resultString = longString;
      if (!resultString)
        Serial.printf ("Could not create a long String s.\n"); // error detected successfuly
      else { Serial.print ("'"); Serial.print (resultString); Serial.println ("'"); }

    // 2.
      resultString = "ABC " + longString + " DEF";
      if (!resultString)
        Serial.printf ("Could not calculate a String s.\n"); // error goes by undetected
      else { Serial.print ("'"); Serial.print (resultString); Serial.println ("'"); } // the output is: ' DEF' 

    // 3.
      resultString = returnLongString (); // failure to create the return String crashes the controller
}

void loop () {

}

My proposal is that each string expression that contains string in "error state" result in string also in "error state", so success could be tested only once even after several String operations. Something like this:

    String s = "abc";
    for (int i = 1; i < 1000; i++)
      s += s.substring (1, 1);
    if (!s) ... // error

Thank you.