Where can I find the difference instructions of these functions?

 
Where can I find the difference instructions of the functions below? I didn't find the differences even though I tried to print the return values.

1. Between DoubleToStr() and DoubleToString()?
2. Between CharToString() and CharToStr() ?
3. Between StringGetCharacter() and StringGetChar()?

You can see the main concern between 'Str' and 'String', between 'Character' and 'Char' indeed.
 

No friend can answer? 

 
Yeah I am irritated by them as well because they seem to be doing exactly the same. None of them is marked deprecated. Therefore it's hard to tell which one of these functions is to be preferred. For me it looks like as if they are remaining parts of the merger between MQL4 and MQL5 and these functions remain intact because of MQL4 and MQL5 compatibility. Still annoying tough.
 
One of each is original mt4-code the other one mt5 code which now has been integrated in mt4. So mt4 provides both mt5 only one of them.
 

Got it. Thank you both! 

Reason: