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以下代码段在 BOOST_FOREACH语句内部进入了一个无限循环，我不知道为什么。据我从 Boost 文档中可以看出，在BOOST_FOREACH循环中使用“break”应该没问题。知道这里可能出了什么问题吗？

std::vector<std::wstring> sectors = getSectors();
if (!_sectorCodes.empty()) {  // _sectorCodes is a std::set<std::wstring>.
    bool ok = false; // did we find the sector code we wanted?
    BOOST_FOREACH(Symbol sector, sectors) {
        if (_sectorCodes.find(sector) != _sectorCodes.end()) {
            ok = true;
            break;
        }
    }
    if (!ok) return NULL;
}

如果我用BOOST_FOREACHfor 循环替换循环（使用迭代器 from sectors.begin()to sectors.end()），那么它工作得很好（没有无限循环）。

版本和附加信息：

  • 提升：1.40.0
  • 海湾合作委员会：4.1.2
  • 架构：x86_64
  • 我只在发布版本中得到这种行为；如果我进行调试构建，那么它会按预期工作。
  • 在 Visual Studio 下编译时，它按预期工作——即没有无限循环。

针对 mkb 的问题，这是我运行时得到的结果gcc -E：

if (!_sectorCodes.empty()) {
 bool ok = false;
 if (boost::foreach_detail_::auto_any_t _foreach_col148 = boost::foreach_detail_::contain( (sectors) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(sectors)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(sectors) : (sectors)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else if (boost::foreach_detail_::auto_any_t _foreach_cur148 = boost::foreach_detail_::begin( _foreach_col148 , (true ? 0 : boost::foreach_detail_::encode_type(sectors, boost::foreach_detail_::is_const_(sectors))) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(sectors)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(sectors) : (sectors)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else if (boost::foreach_detail_::auto_any_t _foreach_end148 = boost::foreach_detail_::end( _foreach_col148 , (true ? 0 : boost::foreach_detail_::encode_type(sectors, boost::foreach_detail_::is_const_(sectors))) , (true ? 0 : boost::foreach_detail_::or_( boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost::foreach_detail_::is_array_(sectors)) , (true ? 0 : boost::foreach_detail_::is_rvalue_( (true ? boost::foreach_detail_::make_probe(sectors) : (sectors)), 0))) , boost::foreach_detail_::and_( boost::foreach_detail_::not_(boost_foreach_is_noncopyable( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)) , boost_foreach_is_lightweight_proxy( boost::foreach_detail_::to_ptr(sectors) , boost_foreach_argument_dependent_lookup_hack_value)))))) {} else for (bool _foreach_continue148 = true; _foreach_continue148 && !boost::foreach_detail_::done( _foreach_cur148 , _foreach_end148 , (true ? 0 : boost::foreach_detail_::encode_type(sectors, boost::foreach_detail_::is_const_(sectors)))); _foreach_continue148 ? boost::foreach_detail_::next( _foreach_cur148 , (true ? 0 : boost::foreach_detail_::encode_type(sectors, boost::foreach_detail_::is_const_(sectors)))) : (void)0) if (boost::foreach_detail_::set_false(_foreach_continue148)) {} else for (Symbol sector = boost::foreach_detail_::deref( _foreach_cur148 , (true ? 0 : boost::foreach_detail_::encode_type(sectors, boost::foreach_detail_::is_const_(sectors)))); !_foreach_continue148; _foreach_continue148 = true) {
  if (_sectorCodes.find(sector) != _sectorCodes.end()) {
   ok = true;
   break;
  }
 }
 if (!ok) return PatternFeatureSet_ptr();
}

这种扩展的一个显着特点是有两个嵌套的 for 循环。我无法弄清楚内部循环和外部循环中发生了什么，但是否有可能（正如大卫所建议的那样）我只是打破了内部循环，而 BOOST_FOREACH 对某些人来说处理得并不正确原因？

4

1 回答 1

4

我敢打赌，简化功能：

std::wstring const* find(std::vector<Symbol> const& sectors) {
    if (!_sectorCodes.empty()) {
        BOOST_FOREACH(Symbol sector, sectors) {
            std::set<Symbol>::const_iterator it = _sectorCodes.find(sector);
            if (it != _sectorCodes.end()) { return &*it; }
        }
    }
    return NULL;
} // find

解决了这个问题。

虽然通过优化，很难知道......但至少你的代码会更具可读性。我没有你的 gcc 版本来测试，我的（或 clang）从来没有遇到过任何问题，所以我只能建议：x

于 2012-05-15T16:06:22.970 回答