类x没有默认构造函数，operator new继承

no default constructor exists for class x, operator new inheritence

本文关键字：operator new 继承 构造函数 默认      更新时间：2023-10-16

我试图实现CUDA博客上给出的统一虚拟内存示例:http://devblogs.nvidia.com/parallelforall/unified-memory-in-cuda-6/

Visual Studio 2013给了我一个错误:没有默认构造函数存在类"Term"

#include "cuda_runtime.h"
#include "device_launch_parameters.h"
#include <stdio.h>
#include <iostream>
#define NUM_ATTRIBUTES 10
class Managed {
public:
    void *operator new(size_t len) {
      void *ptr;
      cudaMallocManaged(&ptr, len);
      std::cout << "custom new for size " << len << 'n';
      return ptr;
    }
    void *operator new[] (size_t len) {
      void *ptr;
      cudaMallocManaged(&ptr, len);
      std::cout << "custom new for size " << len << 'n';
      return ptr;
    }
    void operator delete(void *ptr) {
        cudaFree(ptr);
    }
};
class Attribute : public Managed {
public:
    int num_levels;
    int num_active_levels;
    int active_levels;
};
class Term : public Managed {
public:
    int num_active_attributes;
    int active_attributes;
    Attribute attribute[NUM_ATTRIBUTES];
    // Unified memory copy constructor allows pass-by-value
    Term (const Term &orig) {
        num_active_attributes = orig.num_active_attributes;
        active_attributes = orig.active_attributes;
        cudaMallocManaged((void **)&attribute,NUM_ATTRIBUTES * sizeof(Attribute));
        memcpy(attribute, orig.attribute, NUM_ATTRIBUTES * sizeof(Attribute));
    }
};
int main()
{
    Term * A = new Term[10];
    getchar();
    return 0;
}

类Term不是继承自父类Managed中定义的新操作符吗?

这与CUDA无关。编译器没有生成默认构造函数，因为您已经提供了另一个构造函数(复制构造函数)。

只是显式请求默认构造函数:

class Term : public Managed {
public:
    ...
    // C++11
    Term() = default;
    // Pre C++11 alternative (although not strictly equivalent)
    Term() {}
    ...
};

还要注意，operator new和构造函数是两个不同的东西:new用于分配存储，构造函数用于将存储初始化为有意义的状态(大致)。

您需要定义一个默认构造函数，该构造函数是数组元素所必需的

class Term : public Managed {
public:
    //...
    Term () {}  // default c-tor
    Term() = default;  // since C++11, note however that there are some 
                       // differences between Term() = default; and Term() {}
                       // they are not equal when value initialization 
                       // is considered
};

没有，因为显式定义的copy-ctor Term( const Term&)禁止编译器生成默认构造函数。关于=default和{}在默认构造函数方面的差异，您可以查看以下内容:

https://stackoverflow.com/a/23698999/1141471

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