c++ - Valgrind 错误，未初始化的值

Question

我创建了一个 C++ 模板化“样本”函数，它使用 Boost 随机数生成器从任何提供多项式分布的对象中采样作为可迭代对象。

/** Sample a value from a multinomial law with coefficient of modalities provided */
template<typename T>
int sample(const T& proportion)
{
  boost::random::uniform_real_distribution<> uni(0.,
                                                 1.);
  boost::variate_generator<boost::random::mt19937&,
                           boost::random::uniform_real_distribution<> > generator(rng_,
                                                                                  uni);
  Real x = generator();
  Real cumProb = 0.; // cumulative probability
  int index = 0;

  for(typename T::const_iterator it = proportion.begin();
      it != proportion.end();
      ++it)
  {
    cumProb += *it;
    if (x < cumProb)
    {
      return index;
    }
    ++index;
  }
  return -1; // to accelerate sampling, no check have been computed on modalities to verify that is it actually a probability distribution
};

例如，当我使用特征向量调用它时(我在其上添加了一个迭代器)，我在 Valgrind 中收到以下错误:

==4917== Conditional jump or move depends on uninitialised value(s)
==4917==    at 0xD7B0A3C: int mixt::MultinomialStatistic::sample<Eigen::Block<Eigen::Matrix<double, -1, -1, 0, -1, -1> const, -1, -1, false> >(Eigen::Block<Eigen::Matrix<double, -1, -1, 0, -1, -1> const, -1, -1, false> const&) (mixt_MultinomialStatistic.h:76)
==4917==    by 0xD7B0538: mixt::ClassSampler::sampleIndividual(int) (mixt_ClassSampler.cpp:63)
==4917==    by 0xD7ADBE6: mixt::IMixtureComposerBase::sStep(int) (mixt_IMixtureComposerBase.cpp:94)
==4917==    by 0xD7ADAF0: mixt::IMixtureComposerBase::sStep() (mixt_IMixtureComposerBase.cpp:68)
==4917==    by 0xD7AC3DE: mixt::SemStrategy::run() (mixt_SEMStrategy.cpp:83)
==4917==    by 0xD74F742: mixtCompCluster(Rcpp::Vector<19, Rcpp::PreserveStorage>, Rcpp::Vector<19, Rcpp::PreserveStorage>, int, double) (mixtCompCluster.cpp:123)
==4917==    by 0xD749A61: RMixtComp_mixtCompCluster (RcppExports.cpp:18)
==4917==    by 0x4F0ADE7: ??? (in /usr/lib/R/lib/libR.so)
==4917==    by 0x4F4981A: Rf_eval (in /usr/lib/R/lib/libR.so)
==4917==    by 0x4F4B92F: ??? (in /usr/lib/R/lib/libR.so)
==4917==    by 0x4F49622: Rf_eval (in /usr/lib/R/lib/libR.so)
==4917==    by 0x4F4A93E: Rf_applyClosure (in /usr/lib/R/lib/libR.so)
==4917== 

行 mixt_MultinomialStatistic.h:76 对应于 if (x < cumProb) .在我看来，此时 x 和 cumProb 都已定义。我该如何调试它？

编辑

根据 Beta 在评论中的建议，我添加了以下虚拟代码:

if (x < 1000.)
{}
if (-1000. < cumProb)
{}
if (x < cumProb)
{ ...

我仍然收到关于 if (x < cumProb) 行的错误报告.

使用 --track-origins=yes 选项启动 valgrind 时，我得到以下指示

==10074==  Uninitialised value was created by a stack allocation

指向指令:

cumProb += *it;

Answer 1

在我的(单元测试)代码中搜索未初始化的值时，我遇到了一个有点类似的问题，发现特征矩阵(和 vector )的值没有在它们的默认构造函数中初始化。我在一个结构中有这样一个 vector ，最终使用如下语句解决了这个问题:

struct MyStruct {
  Eigen::Vector2f myVector;
};

MyStruct myStruct{};  // Does not initialize myVector's values!
std::cout << "myVec = " << myStruct.myVector << std::endl; // Causes valgrind to warn about uninitialized variables
myStruct.myVector = Eigen::Vector2f(0.0f, 0.0f);
std::cout << "myVecInit = " << myStruct.myVector << std::endl; // No valgrind warning

请注意，我很难对此进行调试，因为当使用 gdb 启动单元测试时， vector 虽然未初始化但恰好包含零。