cpp/io/istrstream/istrstream

Constructs new std and its underlying std.

@1,2@ Constructs the underlying std by calling and initializes the base class with the address of the strstreambuf. The behavior is undefined if is not pointing at an element of a null-terminated array.

@3,4@ Constructs the underlying std by calling and initializes the base class with the address of the strstreambuf. The behavior is undefined if is not pointing at an element of an array whose length is at least  elements.