Question

这个问题在C ++中。我试图动态分配一个指向对象的数组。我知道我可以使用矢量容器，但练习的重点不是......

以下是代码：

void HealthClub::AddHealthClubDevice ( char* HealthClubDeviceName )
{                                       //We added NumberOfDevices as an attribute, so we won't have to use sizeof all the time
    if (NumberOfDevices==0)  // This is for the first device we want to add
    {
        HealthClubDevices = new Device*[1];
        HealthClubDevices[0]= new Device(HealthClubDeviceName);
        NumberOfDevices++;
    }
    else        // Here we did realloc manually...
    {
        Device** tempHealthClubDevices;
        tempHealthClubDevices = new Device*[++NumberOfDevices];  //this is where we see the first sign of a problem, The tempHealthClubDevices is not allocated properly

        for (int i=0 ; i<(NumberOfDevices-1) ; i++)
         tempHealthClubDevices[i]=HealthClubDevices[i];
        delete[] HealthClubDevices;          
        HealthClubDevices = tempHealthClubDevices;
        HealthClubDevices[NumberOfDevices-1]= new Device(HealthClubDeviceName);
   }
}

Device **对象没有正确分配，它们的大小永远不会增长，它们总是一个元素。有谁知道为什么？谢谢！

Answer 1

无法重现您的问题。具体来说，这里是我编译并成功运行的所有骨架代码 - 您的方法加上最小的脚手架，使其成为一个完整的程序：

#include <iostream>

struct Device {
  char* name;
  Device(char* n) {name = n;}
};

struct HealthClub {
  int NumberOfDevices;
  Device** HealthClubDevices;
  HealthClub() { NumberOfDevices = 0;}
  void AddHealthClubDevice(char *);
};

std::ostream& operator<<(std::ostream& o, const HealthClub& h) {
  o << h.NumberOfDevices << " devices:" << std::endl;
  for(int i=0; i<h.NumberOfDevices; ++i) {
    o << "  " << h.HealthClubDevices[i]->name << std::endl;
  }
  o << "That's all!\n" << std::endl;
  return o;
}

void HealthClub::AddHealthClubDevice ( char* HealthClubDeviceName )
{                                       //We added NumberOfDevices as an attribute, so we won't have to use sizeof all the time
    if (NumberOfDevices==0)  // This is for the first device we want to add
    {
        HealthClubDevices = new Device*[1];
        HealthClubDevices[0]= new Device(HealthClubDeviceName);
        NumberOfDevices++;
    }
    else        // Here we did realloc manually...
    {
        Device** tempHealthClubDevices;
        tempHealthClubDevices = new Device*[++NumberOfDevices];  //this is where we see the first sign of a problem, The tempHealthClubDevices is not allocated properly

        for (int i=0 ; i<(NumberOfDevices-1) ; i++)
         tempHealthClubDevices[i]=HealthClubDevices[i];
        delete[] HealthClubDevices;          
        HealthClubDevices = tempHealthClubDevices;
        HealthClubDevices[NumberOfDevices-1]= new Device(HealthClubDeviceName);
   }
}

int main() {
  HealthClub h;
  std::cout << h;
  h.AddHealthClubDevice("first");
  std::cout << h;
  h.AddHealthClubDevice("second");
  std::cout << h;
  h.AddHealthClubDevice("third");
  std::cout << h;
  return 0;
}

编译很好，即使是--pedantic，当运行时发出：

$ ./a.out 
0 devices:
That's all!

1 devices:
  first
That's all!

2 devices:
  first
  second
That's all!

3 devices:
  first
  second
  third
That's all!

根据需要。所以，你的问题的原因必须在别的地方。鉴于您的真实程序失败（您没有告诉我们具体如何）和这个成功的最小程序，您可以“通过二分插值”来构建最小的失败案例 - 如果仍然没有告诉您问题所在发布最小失败案例和小于它的一个epsilon仍然成功作为SO问题肯定能得到你需要的帮助（一定要指定编译器，操作系统等）。

指针对象的动态分配

1 个答案: