If this object is in putback mode, return the number of characters remaining to be read in the putback buffer, and otherwise the number of characters remaining in the file to be read. Return a non-negative number of characters on success and a negative value otherwise. The behavior is undefined unless this object is in input mode and the file descriptor is associated with a regular file.
Declared in <bdls_fdstreambuf.h>
virtual
std::streamsize
showmanyc() override;