the function String::c_ptr() has a debug assert to ensure there was room for a /0 terminator. This may be false in the following series.
Start with a string where str_length == Alloced_length - 1.
Append a single character such that this is called:
The character is added, wiping out the /0 and creating a situation where str_length == Alloced_length and if c_ptr() is called next, the debug assert aborts.