problem of copying a String with nul byte in the middle

[Dvanoska]

After uploading my sketch (using Arduino 1.6.8 and Arduino Uno),

void loop()
{

  String str1 = "ACDEFG";
  String str2 = "HIP";

  String str3 = str1 + '\0' + str2;

  Serial.println(str1);
  Serial.println(str1.length());
  Serial.println(str2);
  Serial.println(str2.length());
  Serial.println(str3);
  Serial.println(str3.length());
  Serial.println();
  delay(10000);
}

I’m expecting to get as a result something like this:

ACDEFG
6
HIP
3
ACDEFG0HIP
10

But the result is:

ACDEFG
6
HIP
3
ACDEFG `ah
10

I.e. if I understand the problem correctly the String object keeps the right length of str3, but while copying the ‘\0’ it decides the string is over, but it’s not. So in str3 I get right symbols before ‘\0’ and some garbage after.

[matthijskooijman]

See also #1936, which I believe fixes this (but is probably outdated and needs a rebase, which I'll happily do if anyone intends to merge it).

[cousteaulecommandant]

Might this be because String::concat(cstr, len) uses strcpy() instead of memcpy()? strcpy() is not precisely good at copying char buffers which might contain null bytes...
(Also if memcpy is used instead it wouldn't be necessary to create a 2-byte array and adding a \0 for String::concat(char))

[matthijskooijman]

@cousteaulecommandant, Yeah, that's exactly one of the things changed by #1936, see c63b861