小编use*_*797的帖子

我正在尝试使用 scipy 的 Voronoi 镶嵌

http://docs.scipy.org/doc/scipy-dev/reference/generated/scipy.spatial.Voronoi.html

但python不会导入它

from scipy.spatial import Voronoi
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name Voronoi

但是，我从 scipy.spatial 导入其他类没有问题

from scipy.spatial import Delaunay

我重复相同的计算两次,但在一次我得到一个浮点异常,而在另一个我没有.

#include <iostream>
#include <cmath>
#include <fenv.h>

using namespace std;

int main(void)
{
  feenableexcept(-1);

  double x,y,z;

  x = 1.0;

  y = (1.0/(24.3*24.0*3600.0))*x;
  cout << "y = " << y << endl;

  z = x/(24.3*24.0*3600.0);
  cout << "z = " << z << endl;

  return 0;
}

我在g ++和clang ++上测试了它,并在两者中得到了以下输出

y = 4.76299e-07
Floating point exception

这是怎么回事？

我有这段代码可以用clang(甚至是-Weverything)编译好,但gcc会发出错误.

#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

class PhonebookWriter
{
public:

  PhonebookWriter(const string& fname):
    fname_(fname), names_(), numbers_() {}

  PhonebookWriter& operator()(const string& name,
                  const string& number)
  {
    names_.push_back(name);
    numbers_.push_back(number);
    return *this;
  }

  ~PhonebookWriter(void)
  {
    ofstream f(fname_.c_str());
    for(size_t i=0;i<names_.size();++i)
      f << names_[i] << " " << numbers_[i] << "\n";
    f.close();
  }

private:
  const string fname_;
  vector<string> names_;
  vector<string> numbers_;
};

namespace {
  void write_guests_data(const string& fname)
  {
    PhonebookWriter(fname)("Mr Foo Bar","12345")("Mrs Bar Foo","54321");
  }
}

int main(void)
{
  write_guests_data("phone_book.txt");

  return …

假设你用c ++编写了一个函数,但是心不在焉地忘记输入这个单词return.在那种情况下会发生什么？我希望编译器会抱怨,或者一旦程序达到这一点,至少会出现一个分段错误.然而,实际发生的事情要糟糕得多:程序会喷出垃圾.不仅如此,实际输出还取决于优化水平!以下是一些演示此问题的代码:

#include <iostream>
#include <vector>

using namespace std;

double max_1(double n1,
         double n2)
{
  if(n1>n2)
    n1;
  else
    n2;
}

int max_2(const int n1,
      const int n2)
{
  if(n1>n2)
    n1;
  else
    n2;
}

size_t max_length(const vector<int>& v1,
          const vector<int>& v2)
{
  if(v1.size()>v2.size())
    v1.size();
  else
    v2.size();
}

int main(void)
{
  cout << max_1(3,4) << endl;
  cout << max_1(4,3) << endl;

  cout << max_2(3,4) << endl;
  cout << max_2(4,3) << endl;

  cout << max_length(vector<int>(3,1),vector<int>(4,1)) << endl;
  cout << max_length(vector<int>(4,1),vector<int>(3,1)) << …