DataArray<T>::diff string comparison error

[BradWhitlock]

The diff method does not appear to compare strings properly if a string has been overwritten into a node that already had a longer string. I assume that it saw that it did not have to reallocate and it stores "quad\0" into the existing buffer. Then diff() subtracts 1 off the end of the char buffer length but that does not reflect the length of the string. So, we end up comparing "quad" vs "quad\0on" and the comparison fails.

1. Can the code encounter non-null terminated strings? Is that why it's even passing a length to std::string?
2. If we change to the typical std::string(const char*) constructor (ignoring any lengths) it works - but my strings are null terminated.

node["elements/shape"] = "polygon";
// some other logic
node["elements/shape"] = "quad";

Then I called some code in a test to compare my in-memory value to a baseline read by relay.

conduit::relay::io::load(filename, "yaml", baseline);
bool equal = !baseline.diff(n, info, tolerance, true);

[cyrush]

@BradWhitlock
Thanks for the report -- this is a bug, and yes it is a consequence of the logic which avoids reallocation.

I think we can specialize the the char8 DataArray case to do the right thing -- respect NULL termed strings.

Related, the set reallocation avoidance logic causes confusion in many of cases.

I would like to change this -- #941 -- but this would be a breaking change with the potential to cause many surprises.

Long term it makes sense to rip the bandaid off, but we would have to make sure conduit users know this is coming.