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libcxx: Fix for basic_stringbuf::seekoff() after r320604. 

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
This commit is contained in:
Peter Collingbourne 2017-12-19 23:33:16 +00:00
parent 7e13aef428
commit 22c651c577
2 changed files with 27 additions and 2 deletions
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5
libcxx/include/sstream
View File

@ -577,6 +577,7 @@ basic_stringbuf<_CharT, _Traits, _Allocator>::seekoff(off_type __off,
if ((__wch & (ios_base::in | ios_base::out)) == (ios_base::in | ios_base::out)
&& __way == ios_base::cur)
return pos_type(-1);
const ptrdiff_t __hm = __hm_ == nullptr ? 0 : __hm_ - __str_.data();
off_type __noff;
switch (__way)
{
@ -590,13 +591,13 @@ basic_stringbuf<_CharT, _Traits, _Allocator>::seekoff(off_type __off,
__noff = this->pptr() - this->pbase();
break;
case ios_base::end:
__noff = __hm_ - __str_.data();
__noff = __hm;
break;
default:
return pos_type(-1);
}
__noff += __off;
if (__noff < 0 || __hm_ - __str_.data() < __noff)
if (__noff < 0 || __hm < __noff)
return pos_type(-1);
if (__noff != 0)
{

24
libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.virtuals/seekoff.pass.cpp
View File

@ -20,6 +20,30 @@
int main()
{
{
std::stringbuf sb(std::ios_base::in);
assert(sb.pubseekoff(3, std::ios_base::beg, std::ios_base::out) == -1);
assert(sb.pubseekoff(3, std::ios_base::cur, std::ios_base::out) == -1);
assert(sb.pubseekoff(-3, std::ios_base::end, std::ios_base::out) == -1);
assert(sb.pubseekoff(3, std::ios_base::beg, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(3, std::ios_base::cur, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(-3, std::ios_base::end, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(0, std::ios_base::beg, std::ios_base::in) == 0);
assert(sb.pubseekoff(0, std::ios_base::cur, std::ios_base::in) == 0);
assert(sb.pubseekoff(0, std::ios_base::end, std::ios_base::in) == 0);
}
{
std::stringbuf sb(std::ios_base::out);
assert(sb.pubseekoff(3, std::ios_base::beg, std::ios_base::in) == -1);
assert(sb.pubseekoff(3, std::ios_base::cur, std::ios_base::in) == -1);
assert(sb.pubseekoff(-3, std::ios_base::end, std::ios_base::in) == -1);
assert(sb.pubseekoff(3, std::ios_base::beg, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(3, std::ios_base::cur, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(-3, std::ios_base::end, std::ios_base::in | std::ios_base::out) == -1);
assert(sb.pubseekoff(0, std::ios_base::beg, std::ios_base::out) == 0);
assert(sb.pubseekoff(0, std::ios_base::cur, std::ios_base::out) == 0);
assert(sb.pubseekoff(0, std::ios_base::end, std::ios_base::out) == 0);
}
{
std::stringbuf sb("0123456789", std::ios_base::in);
assert(sb.pubseekoff(3, std::ios_base::beg, std::ios_base::out) == -1);