在 C++ 中，如何构建以对象为成员变量的数据结构？答案

【问题标题】：In c++, how do I build a data structure with objects as member variables?在 C++ 中，如何构建以对象为成员变量的数据结构？
【发布时间】：2017-06-27 07:10:23
【问题描述】：

我最近开始了一项涉及 cpp 编码的研究，我完全不熟悉，并且遇到了一堆问题：

默认构造函数
使用对象作为成员变量创建数据结构。

我的程序设置需要是这样的：

我需要创建一个数据结构，它的成员变量之一是 Wave 对象数组：Wave[ ]i>
Wave 实际上是从波形文件中读取的（我的代码链接到一些外部库来执行此操作）
每个 Wave 都有一个 GPS 对象。
每个 GPS 对象都有大约 15 个 int 或 double 类型的成员变量

这就是我的 GPS.hpp 类的样子 -

 #ifndef GPS_HPP_
    #define GPS_HPP_

    #include <iostream>
    #include <fstream>
    #include "pulsereader.hpp"
    #include "pulsewriter.hpp"

    class GPS{

    public:
      //possible parameters
      double gpsTime;
      double xAnchor, yAnchor, zAnchor;
      double xTarget, yTarget, zTarget;
      double xDeviation, yDeviation, zDeviation;
      double xFirst, yFirst, zFirst;
      double xLast, yLast, zLast;
      unsigned char edge;
      unsigned char facet;
      unsigned char scanDirection;
      unsigned char intensity;

      PULSEreadOpener pOpener;
      PULSEreader *pReader;
      PULSEscanner scanner;

      GPS();

      void setGPSInformation();
      void writeToFileGPSInformation(std::string fileName);

    };
    #endif /* GPS_HPP_ */ 

This is my GPS.cpp class: 

    #include <iostream>
#include "GPS.hpp"

//Default constructor
GPS::GPS(){
  // enter default values
  xAnchor = 0;
  yAnchor = 0;
  zAnchor = 0;
  xTarget = 0;
  yTarget = 0;
  zTarget = 0;
  xFirst = 0;
  yFirst = 0;
  zFirst = 0;
  xLast = 0;
  yLast = 0;
  zLast = 0;
  edge = 0;
  facet = 0;
  scanDirection = 0;
  intensity = 0;
}


void GPS::setGPSInformation(){

  gpsTime = pReader->pulse.get_t();
  // Compute anchor, target and direction
  pReader->pulse.compute_anchor_and_target_and_dir();
  xAnchor = pReader->pulse.get_anchor_x();
  yAnchor = pReader->pulse.get_anchor_y();
  zAnchor = pReader->pulse.get_anchor_z();
  xTarget = pReader->pulse.get_target_x();
  yTarget = pReader->pulse.get_target_y();
  zTarget = pReader->pulse.get_target_z();
  // Compute first and last returning Values
  pReader->pulse.compute_first_and_last();
  xFirst = pReader->pulse.get_first_x();
  yFirst = pReader->pulse.get_first_y();
  zFirst = pReader->pulse.get_first_z();
  xLast = pReader->pulse.get_last_x();
  yLast = pReader->pulse.get_last_y();
  zLast = pReader->pulse.get_last_z();

  edge = pReader->pulse.edge_of_scan_line;
  scanDirection = pReader->pulse.scan_direction;
  facet = pReader->pulse.mirror_facet,
  intensity = pReader->pulse.intensity;
}

/*
 * Writes all GPS information to a csv file
 */
void GPS::writeToFileGPSInformation(std::string fileName){
  long long pulseIndex = 0;
  FILE *scanout;
  scanout = fopen("gps.csv", "w");
  fprintf(scanout, "Pulse Index, GPS Time, X Anchor, Y Anchor,  Z Anchor, \
                    X Target, Y Target, Z Target, X First, \
                    Y First, Z First, X Last, Y Last, Z Last, \
                    edge, Scan Direction, facet, intensity\n");

  pOpener.set_file_name(fileName.c_str());
  pReader = pOpener.open();

  pReader->seek(0);
  while(pReader->read_pulse()) {
    gpsTime = pReader->pulse.get_t();

    pReader->pulse.compute_anchor_and_target_and_dir();
    xAnchor = pReader->pulse.get_anchor_x();
    yAnchor = pReader->pulse.get_anchor_y();
    zAnchor = pReader->pulse.get_anchor_z();
    xTarget = pReader->pulse.get_target_x();
    yTarget = pReader->pulse.get_target_y();
    zTarget = pReader->pulse.get_target_z();

    pReader->pulse.compute_first_and_last();
    xFirst = pReader->pulse.get_first_x();
    yFirst = pReader->pulse.get_first_y();
    zFirst = pReader->pulse.get_first_z();
    xLast = pReader->pulse.get_last_x();
    yLast = pReader->pulse.get_last_y();
    zLast = pReader->pulse.get_last_z();

    edge = pReader->pulse.edge_of_scan_line;
    scanDirection = pReader->pulse.scan_direction;
    facet = pReader->pulse.mirror_facet,
    intensity = pReader->pulse.intensity;

    fprintf(scanout, "%lld,%.8lf,   \
                      %lf,%lf,%lf,  \
                      %lf,%lf,%lf,  \
                      %lf,%lf,%lf,  \
                      %lf,%lf, %lf, \
                      %d,%d,%d,%d,\n", 
            pulseIndex, gpsTime, 
            xAnchor, yAnchor, zAnchor, 
            xTarget, yTarget, zTarget,
            xFirst, yFirst, zFirst,
            xLast, yLast, zLast, 
            edge, scanDirection, facet, intensity) ;
    pulseIndex++;
  }
}

这是我的 GPS.cpp：

#include <iostream>
#include "GPS.hpp"

//Default constructor
GPS::GPS(){
  // enter default values
  xAnchor = 0;
  yAnchor = 0;
  zAnchor = 0;
  xTarget = 0;
  yTarget = 0;
  zTarget = 0;
  xFirst = 0;
  yFirst = 0;
  zFirst = 0;
  xLast = 0;
  yLast = 0;
  zLast = 0;
  edge = 0;
  facet = 0;
  scanDirection = 0;
  intensity = 0;
}


void GPS::setGPSInformation(){

  gpsTime = pReader->pulse.get_t();
  // Compute anchor, target and direction
  pReader->pulse.compute_anchor_and_target_and_dir();
  xAnchor = pReader->pulse.get_anchor_x();
  yAnchor = pReader->pulse.get_anchor_y();
  zAnchor = pReader->pulse.get_anchor_z();
  xTarget = pReader->pulse.get_target_x();
  yTarget = pReader->pulse.get_target_y();
  zTarget = pReader->pulse.get_target_z();
  // Compute first and last returning Values
  pReader->pulse.compute_first_and_last();
  xFirst = pReader->pulse.get_first_x();
  yFirst = pReader->pulse.get_first_y();
  zFirst = pReader->pulse.get_first_z();
  xLast = pReader->pulse.get_last_x();
  yLast = pReader->pulse.get_last_y();
  zLast = pReader->pulse.get_last_z();

  edge = pReader->pulse.edge_of_scan_line;
  scanDirection = pReader->pulse.scan_direction;
  facet = pReader->pulse.mirror_facet,
  intensity = pReader->pulse.intensity;
}

/*
 * Writes all GPS information to a csv file
 */
void GPS::writeToFileGPSInformation(std::string fileName){
  long long pulseIndex = 0;
  FILE *scanout;
  scanout = fopen("gps.csv", "w");
  fprintf(scanout, "Pulse Index, GPS Time, X Anchor, Y Anchor,  Z Anchor, \
                    X Target, Y Target, Z Target, X First, \
                    Y First, Z First, X Last, Y Last, Z Last, \
                    edge, Scan Direction, facet, intensity\n");

  pOpener.set_file_name(fileName.c_str());
  pReader = pOpener.open();

  pReader->seek(0);
  while(pReader->read_pulse()) {
    gpsTime = pReader->pulse.get_t();

    pReader->pulse.compute_anchor_and_target_and_dir();
    xAnchor = pReader->pulse.get_anchor_x();
    yAnchor = pReader->pulse.get_anchor_y();
    zAnchor = pReader->pulse.get_anchor_z();
    xTarget = pReader->pulse.get_target_x();
    yTarget = pReader->pulse.get_target_y();
    zTarget = pReader->pulse.get_target_z();

    pReader->pulse.compute_first_and_last();
    xFirst = pReader->pulse.get_first_x();
    yFirst = pReader->pulse.get_first_y();
    zFirst = pReader->pulse.get_first_z();
    xLast = pReader->pulse.get_last_x();
    yLast = pReader->pulse.get_last_y();
    zLast = pReader->pulse.get_last_z();

    edge = pReader->pulse.edge_of_scan_line;
    scanDirection = pReader->pulse.scan_direction;
    facet = pReader->pulse.mirror_facet,
    intensity = pReader->pulse.intensity;

    fprintf(scanout, "%lld,%.8lf,   \
                      %lf,%lf,%lf,  \
                      %lf,%lf,%lf,  \
                      %lf,%lf,%lf,  \
                      %lf,%lf, %lf, \
                      %d,%d,%d,%d,\n", 
            pulseIndex, gpsTime, 
            xAnchor, yAnchor, zAnchor, 
            xTarget, yTarget, zTarget,
            xFirst, yFirst, zFirst,
            xLast, yLast, zLast, 
            edge, scanDirection, facet, intensity) ;
    pulseIndex++;
  }
}

这是我目前用来将 GPS 信息写入 csv 的驱动程序类。

#include <iostream>
#include "CmdLine.hpp"
#include "ScannerInformation.hpp"
#include "GPS.hpp"


using namespace std;

int main (int argc, char *argv[]){

  CmdLine cmdLineArgs;
  cmdLineArgs.parse(argc,argv);

  if(cmdLineArgs.printUsageMessage == true){
    std::cout << cmdLineArgs.getUsageMessage() << std::endl;
  }
  else{
    std::string fileName = cmdLineArgs.getInputFileName();
    ScannerInformation scannerInfo;
    scannerInfo.writeToFileScannerInformation(fileName);

    GPS gpsInfo;
    gpsInfo.writeToFileGPSInformation(fileName);

  }

  return 0;
}

除了将 GPS 信息写入 CSV 之外，我还希望能够在我的驱动程序类中访问每个 Wave 的 gps 信息（类似这样）-

std::cout << wave.gpsInfo.xAnchor;

如何编写我的 Wave.hpp 和 cpp 以使其具有 GPS 对象作为其成员变量，然后如何从我的驱动程序文件中访问波形对象的 gps 信息？

#include "GPS.hpp"

class Wave {    
private:
  GPS gps;

public:
 //What kind of methods would I use here?
};

【问题讨论】：

private: , public: 在全球范围内？？
这并不接近编译。这是你的真实代码吗？看看MCVE
很抱歉，我是 stackoverflow 和 c++ 的新手，我还在忙着解决问题。我已经编辑了这个问题，使其更加准确，并包含了额外的代码。任何帮助将不胜感激。

标签： c++ object data-structures constructor

【解决方案1】：

我来答题了。

你就去做吧！一个例子：

struct Pos
{
    int x = 0;
    int y = 0;
};

struct Line
{
    Pos start;
    Pos end;
};

一些注意事项：

Pos 和 Line 都是类。不要让关键字struct 欺骗您。由于两者都没有类不变量，因此它们的数据可以是公开的。
除非必须，否则不要编写构造函数。成员的初始化可以在类中完成。
C++ 具有值语义；这意味着类型通常表现像 int 一样，没有特殊处理来区分对象和其他对象类型。

【讨论】：

赞成，因为在这种情况下使用结构的想法。

【解决方案2】：

类似的东西：

#include "GPS.hpp"
#include "OutgoingWave.hpp"
#include "IncomingWave.hpp"

class Wave {    
private:
  GPS _gps;
  OutgoingWave _ow;
  IncomingWave _iw;    
public:
  const GPS& gps() const { return _gps; }
  const OutgoingWave& ow() const { return _ow; }
  const IncomingWave& iw() const { return _iw; }
};

确保返回的引用不会超过 Wave 对象（如果是这种情况，则返回值，但这会导致额外的复制）。类GPS、IncomingWave 和OutgoingWave 可以转换为structs，以便对所有成员具有默认的公共访问权限。顺便说一句，您发布的代码无法编译，public 和 private 修饰符需要在一个类中。

【讨论】：

【解决方案3】：

要准确获取您在问题中要求的代码，您需要公开成员。最好使用结构来完成，因为它的成员默认情况下是公共的。

struct Wave {
  GPS gpsInfo;
};

struct GPS {
  double gpsTime;
  double xAnchor; //you may want to use a Point class or struct
  ...
  unsigned char intensity;
};

这样您就不需要任何额外的方法（即 getter 和 setter）。这种方法没有任何问题，但是您基本上失去了添加功能的可能性，例如输入的完整性检查。如果 Wave 或 GPS 具有更复杂的状态并且成员相互依赖于彼此的值，您可能希望使用类并通过使用 getter 和 setter 封装对其成员的访问。

【讨论】：

类也可以使用struct关键字定义
@weeska 我的问题真的很模糊，我最初遗漏了很多代码。对于那个很抱歉。此后我对其进行了编辑，使其更加清晰。