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tolerate padding in mbstate_t

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Padding in mbstate_t objects may get the memcmp to fail.
Attempt to avoid the failure with zero initialization.


for  libstdc++-v3/ChangeLog

	* testsuite/27_io/fpos/mbstate_t/1.cc: Zero-init mbstate_t.
This commit is contained in:
Alexandre Oliva 2020-01-23 16:36:34 -03:00 committed by Alexandre Oliva
parent 32667e04c7
commit 7a900bceca
2 changed files with 25 additions and 7 deletions
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4
libstdc++-v3/ChangeLog
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@ -1,3 +1,7 @@
2020-01-23 Alexandre Oliva <oliva@adacore.com>
* testsuite/27_io/fpos/mbstate_t/1.cc: Zero-init mbstate_t.
2020-01-23 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/91947

28
libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc
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@ -28,24 +28,38 @@
void test01()
{
typedef std::mbstate_t state_type;
state_type state01 = state_type();
state_type state02 = state_type();
// Use zero-initialization of the underlying memory so that padding
// bytes, if any, stand a better chance of comparing the same.
// Zero-initialized memory is guaranteed to be a valid initial
// state. This doesn't quite guarantee that any padding bits won't
// be overwritten when copying from other instances that haven't
// been fully initialized: this data type is compatible with C, so
// it is likely plain old data, but it could have a default ctor
// that initializes only the relevant fields, whereas copy-ctor and
// operator= could be implemented as a full-object memcpy, including
// padding bits, rather than fieldwise copying. However, since
// we're comparing two values copied from the same state_type
// instance, if padding bits are copied, we'll get the same for both
// of them, and if they aren't, we'll keep the values we initialized
// them with, so this should be good.
state_type state[2];
std::memset(state, 0, sizeof (state));
std::streampos pos01(0);
std::streampos pos02(0);
// 27.4.3.1 fpos members
// void state(state_type s);
// state_type state();
// XXX Need to have better sanity checking for the mbstate_t type,
// or whatever the insantiating type for class fpos happens to be
// or whatever the instantiating type for class fpos happens to be
// for streampos, as things like equality operators and assignment
// operators, increment and deincrement operators need to be in
// place.
pos01.state(state02);
state01 = pos01.state();
VERIFY( std::memcmp(&state01, &state02, sizeof(state_type)) == 0 );
pos01.state(state[1]);
state[0] = pos01.state();
VERIFY( std::memcmp(&state[0], &state[1], sizeof(state_type)) == 0 );
}
int main()