Valgrind抱怨std :: string构造函数中的字节丢失了

Question

我是valgrind的新手,所以这可能会错过解释输出.Valgrind似乎认为字节在以下几行中丢失:

if ( mysqlpp::StoreQueryResult result = query.store() ){
   for ( size_t i = 0; i < result.num_rows(); ++i ){
       hash = std::string( result[i]["hash"].data(), result[i]["hash"].length() );
       label = std::string( result[i]["label"].data(), result[i]["label"].length() );
       keywords = std::string( result[i]["keywords"].data(), result[i]["keywords"].length() );
       task_raw = std::string( result[i]["task"].data(), result[i]["task"].length() );
       solution_raw = std::string( result[i]["solution"].data(), result[i]["solution"].length() );

事实上,每当有一个std :: string以这种方式构建时,它就会抱怨^^.如果我正在复制的方式不正确,或者结果是以某种方式泄露,我无法弄清楚这是否是误报.

有趣的是,它抱怨另一段不使用mysql ++的代码,但同样使用了一个字符串构造函数:

for ( auto & f : frames ){
  for ( unsigned int i = 0; i < f.getTask().size(); i++ ){
     if ( i + 1 < f.getTask().size() ){
        auto t = f.getTask()[i].value();
        auto n = f.getTask()[i+1].value();
        pairs.push_back( std::string( t + n ) );

构造和推回字符串的行可能会丢失.然后给出了malloc,operator new,std :: string等的详细输出.

从std :: istringstream复制字符串时,同样的故事再次出现:

std::copy( std::istream_iterator<std::string>(iss), std::istream_iterator<std::string>(), std::back_inserter<std::vector<std::string> >(tokens));

那些假阳性吗？是否与使用C++ 0x有关？或者那些可能源于我还没有发现泄漏的地方的合法泄漏？

编辑

以下是重复出现的valgrind警告示例:

==18141== 9,555 bytes in 147 blocks are possibly lost in loss record 250 of 256
==18141==    at 0x4C28BED: malloc (vg_replace_malloc.c:263)
==18141==    by 0x7CA74C: operator new(unsigned long) (in trunk/Build/icarus)
==18141==    by 0x7B4208: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /trunk/Build/icarus)
==18141==    by 0x7B5904: char* std::string::_S_construct<char const*>(char const*, char const*, std::allocator<char> const&, std::forward_iterator_tag) (in trunk/Build/icarus)
==18141==    by 0x7B5A7C: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in trunk/Build/icarus)
==18141==    by 0x610D65: Frame::mySQLloadFrameFromExample(std::string const&) (Frame.cpp:80)
==18141==    by 0x6103FB: Frame::Frame(std::string const&) (Frame.cpp:5)
==18141==    by 0x6054DB: Domain::mySQLloadFrames() (Domain.cpp:90)
==18141==    by 0x60489D: Domain::Domain(std::string) (Domain.cpp:7)
==18141==    by 0x628876: DomainController::loadDomainData() (DomainController.cpp:33)
==18141==    by 0x628582: DomainController::DomainController() (DomainController.cpp:5)
==18141==    by 0x627002: Controller::Controller() (Controller.cpp:26)

它们几乎都是相同的,唯一的区别是代码中的实际行(即:字符串构造函数行).

第二种警告是:

==18141== 3,562 bytes in 137 blocks are possibly lost in loss record 242 of 256
==18141==    at 0x4C28BED: malloc (vg_replace_malloc.c:263)
==18141==    by 0x7CA74C: operator new(unsigned long) (in trunk/Build/icarus)
==18141==    by 0x7B4208: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in trunk/Build/icarus)
==18141==    by 0x7B4EFA: std::string::_Rep::_M_clone(std::allocator<char> const&, unsigned long) (in trunk/Build/icarus)
==18141==    by 0x7B4FDF: std::string::reserve(unsigned long) (in trunk/Build/icarus)
==18141==    by 0x784F2F: std::basic_istream<char, std::char_traits<char> >& std::operator>><char, std::char_traits<char>, std::allocator<char> >(std::basic_istream<char, std::char_traits<char> >&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&) (in trunk/Build/icarus)
==18141==    by 0x61208E: std::istream_iterator<std::string, char, std::char_traits<char>, long>::_M_read() (stream_iterator.h:121)
==18141==    by 0x613405: std::istream_iterator<std::string, char, std::char_traits<char>, long>::operator++() (stream_iterator.h:95)
==18141==    by 0x6131BC: std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > std::__copy_move<false, false, std::input_iterator_tag>::__copy_m<std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > >(std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > >) (stl_algobase.h:298)
==18141==    by 0x612D09: std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > std::__copy_move_a<false, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > >(std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > >) (stl_algobase.h:384)
==18141==    by 0x6121FD: std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > std::__copy_move_a2<false, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > >(std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > >) (stl_algobase.h:422)
==18141==    by 0x611C6A: std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > std::copy<std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > > >(std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::istream_iterator<std::string, char, std::char_traits<char>, long>, std::back_insert_iterator<std::vector<std::string, std::allocator<std::string> > >) (stl_algobase.h:454)

这似乎与上面提到的std :: istringstream代码有关.