Padding in mbstate_t objects may get the memcmp to fail. Attempt to avoid the failure with zero initialization.
Regstrapped on x86_64-linux-gnu, and also tested on a platform that used to fail because of padding in std::mbstate_t. Ok to install? for libstdc++-v3/ChangeLog * testsuite/27_io/fpos/mbstate_t/1.cc: Zero-init mbstate_t. --- testsuite/27_io/fpos/mbstate_t/1.cc | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc index f92d68f..559bd8d 100644 --- libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc +++ libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc @@ -28,8 +28,24 @@ 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 (or was this meant to take one of them from pos02 rather + // than both from pos01?), 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); @@ -39,13 +55,13 @@ void test01() // 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() -- Alexandre Oliva, freedom fighter he/him https://FSFLA.org/blogs/lxo Free Software Evangelist Stallman was right, but he's left :( GNU Toolchain Engineer FSMatrix: It was he who freed the first of us FSF & FSFLA board member The Savior shall return (true);