String class (WString.cpp/.h) new functions

[TobiasKnauss]

See
https://groups.google.com/a/arduino.cc/forum/#!topic/developers/ryrMAJiqwf0

summary:

• constructors enhanced with "unsigned int bufferSize = 0" to allow a preset size for the internal char array malloc.
• void String::setReservePercentage (unsigned char percentage)
  adds a reserve on the realloc so that further small String concats don't have to realloc every time.
• void String::setDefaultReservePercentage (unsigned char percentage)
  sets a default value for reservePercentage, that is used when creating new Strings.

These 3 functions operate in init() and reserve().

Added String manipulation functions:
// modification
// notice: void function (...) operates on the object and returns void
// String functionC (...) operates on a copy of the object and returns the copy (C=Copy)
// String* functionS (...) operates on the object and returns a pointer to the object (S=Self)

existing before #### void replace (char find, char replace);

String replaceC(char find, char replace);
String* replaceS(char find, char replace);

existing before #### void replace (const String& find, const String& replace);

String replaceC(const String& find, const String& replace);
String* replaceS(const String& find, const String& replace);

existing before #### void remove (unsigned int index);

String removeC(unsigned int index);
String* removeS(unsigned int index);

existing before #### void remove (unsigned int index, unsigned int count);

String removeC(unsigned int index, unsigned int count);
String* removeS(unsigned int index, unsigned int count);

existing before #### void toLowerCase (void);

String toLowerCaseC(void);
String* toLowerCaseS(void);

existing before #### void toUpperCase (void);

String toUpperCaseC(void);
String* toUpperCaseS(void);

existing before #### void trim (void);

String trimC(void);
String* trimS(void);
void trim (char remove);
String trimC(char remove);
String* trimS(char remove);
void trimStart (void);
String trimStartC(void);
String* trimStartS(void);
void trimStart (char remove);
String trimStartC(char remove);
String* trimStartS(char remove);
void trimEnd (void);
String trimEndC(void);
String* trimEndS(void);
void trimEnd (char remove);
String trimEndC(char remove);
String* trimEndS(char remove);
void padLeft (unsigned int newlength);
String padLeftC(unsigned int newlength);
String* padLeftS(unsigned int newlength);
void padLeft (unsigned int newlength, char add);
String padLeftC(unsigned int newlength, char add);
String* padLeftS(unsigned int newlength, char add);
void padRight (unsigned int newlength);
String padRightC(unsigned int newlength);
String* padRightS(unsigned int newlength);
void padRight (unsigned int newlength, char add);
String padRightC(unsigned int newlength, char add);
String* padRightS(unsigned int newlength, char add);
void cropLeft (unsigned int count);
String cropLeftC(unsigned int count);
String* cropLeftS(unsigned int count);
void cropRight (unsigned int count);
String cropRightC(unsigned int count);
String* cropRightS(unsigned int count);
void keepLeft (unsigned int count);
String keepLeftC(unsigned int count);
String* keepLeftS(unsigned int count);
void keepRight (unsigned int count);
String keepRightC(unsigned int count);
String* keepRightS(unsigned int count);

detailed descriptions at
#4870

[cousteaulecommandant]

Instead of adding the -S versions, wouldn't it be better to just replace the functions returning void with functions returning String&? That way you would be able to do things like myString.trim().replace('\\','/').toLowerCase().
Also I think it would be simpler to just add a String copy(void) method for when you want to explicitly operate on a copy of the String rather than adding a lot of new -C functions potentially increasing the library size (plus I think the -C suffix is a bit cryptic).
...well, maybe not copy(), as this already seems to be used for something different; maybe dup() or something like that.

[BillyDonahue]

@cousteaulecommandant, can't the proposed s.dup() already be expressed as String(s)?

[cousteaulecommandant]

@cousteaulecommandant, can't the proposed s.dup() already be expressed as String(s)?

Yes, but I think string2 = string1.dup().trim().replace('\\','/').toLowerCase() might look more consistent than string2 = String(string1).trim().replace('\\','/').toLowerCase(), if this "chain of methods" approach is to be followed.
Then again, maybe an explicit string creation is a better idea than a "method"-based copy, so you might be right. I was just proposing a direct alternative to the functions proposed here.

[facchinm]

I agree with #4890 (comment) , and this discussion should be migrated to https://github.com/arduino/ArduinoCore-api since it allows very interesting stuff. We are not going to add C and S versions so I'm closing this PR