小编use*_*632的帖子

我试图使用Python函数计算文件中的行数.在当前目录中,当os.system("ls")找到文件时,命令subprocess.Popen(["wc -l filename"], stdout=subprocess.PIPE)不起作用.

这是我的代码:

>>> import os
>>> import subprocess
>>> os.system("ls")
sorted_list.dat
0
>>> p = subprocess.Popen(["wc -l sorted_list.dat"], stdout=subprocess.PIPE)File "<stdin>", line 1, in <module>
File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 710, in __init__
    errread, errwrite)
File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 1335, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

我可以用Gnuplot 5.0绘制平行坐标图.例如:

plot "ranking_top10.dat" using 4:5:6:7:8:2 with parallel lt 1 lc variable

将绘制5个轴和不同颜色的线条.但是,我想将键与每个行关联起来.例如,我想将一个键(字符串)与紫色线相关联,并在图中显示它.怎么做？

这是我的代码:

class NO {
  public:
    NO(std::string& name):nameValue(name){};

  private:
    std::string& nameValue;           // this is now a reference

};

int main(){

  int b=10,c=20;
  int& d=b;
  d=c;

  std::string p="alpha", q="beta";

  NO x(p), y(q);
  x=y;

  return 0;

}

我收到错误:

"non-static reference member ‘std::string& NO::nameValue’, can’t use default assignment operator"

当我可以使用内置类型执行相同操作时,为什么不能使用引用成员重新分配对象？

谢谢

我有以下代码:

void endConditionalFlowsBetweenSets(const list<unsigned int>& sourceSet, const     list<unsigned int>& endSet){
    //TODO: Optimize
    //ending previous flows between the two sets
    list<unsigned int>::iterator itS;
    list<unsigned int>::iterator itE;
    for(itS=sourceSet.begin();itS!=sourceSet.end();itS++)
        for(itE=endSet.begin();itE!=endSet.end();itE++)
            if(*itS!=*itE && linkIndex[*itS][*itE].index==-1)   
                endFlow(*itS,*itE);
}

编译后我得到错误: no known conversion for argument 1 from ‘std::list<unsigned int>::const_iterator {aka std::_List_const_iterator<unsigned int>}’ to ‘const std::_List_iterator<unsigned int>&’

这是为什么？我只是通过引用传递一个列表并创建一个迭代器来迭代它.

我尝试了以下代码(从learncpp.com修改)

#include <iostream>
#include <string>

using namespace std;

class Point2D
{
private:
int m_nX;
int m_nY;

public:
// A default constructor
Point2D()
    : m_nX(0), m_nY(0)
{
}

// A specific constructor
Point2D(int nX, int nY)
    : m_nX(nX), m_nY(nY)
{
  cout<<"Point is created"<<endl;
}

~Point2D(){cout<<"Point is destroyed"<<endl;}

// An overloaded output operator
friend std::ostream& operator<<(std::ostream& out, const Point2D &cPoint)
{
    out << "(" << cPoint.GetX() << ", " << cPoint.GetY() << ")";
    return out;
}

// Access functions
void SetPoint(int nX, …