As a result of this change, the basic_stringbuf constructor that
takes a mode ends up leaving __hm_ set to 0, causing the comparison
"__hm_ - __str_.data() < __noff" in seekoff() to succeed, which caused
the function to incorrectly return -1. The fix is to account for the
possibility of __hm_ being 0 when computing the distance from __hm_
to the start of the string.
Differential Revision: https://reviews.llvm.org/D41319
llvm-svn: 321124
Summary:
[libcxx] Fix basic_stringbuf constructor
The C++ Standard [stringbuf.cons]p1 defines the effects of the basic_stringbuf
constructor that takes ios_base::openmode as follows:
Effects: Constructs an object of class basic_stringbuf, initializing the
base class with basic_streambuf(), and initializing mode with which.
Postconditions: str() == "".
The default constructor of basic_streambuf shall initialize all its
pointer member objects to null pointers [streambuf.cons]p1.
Currently libc++ calls "str(string_type());" in the aforementioned constructor
setting basic_streambuf's pointers to a non-null value.
This patch removes the call (note that the postcondition str() == ""
remains valid because __str_ is default-initialized) and adds a test checking
that the basic_streambuf's pointers are null after construction.
Thanks Mikhail Maltsev for the patch.
Reviewers: EricWF, mclow.lists
Reviewed By: mclow.lists
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D40707
llvm-svn: 320604
Peter Collingbourne