将结构转换为与其第一组成员匹配的类型的正确方法是什么? [英] What is the correct way to cast a struct to a type that matches its first set of members?

问题描述

请考虑WinAPI中的以下结构:

Please consider the following structs from the WinAPI:

typedef struct _PROCESS_MEMORY_COUNTERS {
  DWORD  cb;
  DWORD  PageFaultCount;
  SIZE_T PeakWorkingSetSize;
  SIZE_T WorkingSetSize;
  SIZE_T QuotaPeakPagedPoolUsage;
  SIZE_T QuotaPagedPoolUsage;
  SIZE_T QuotaPeakNonPagedPoolUsage;
  SIZE_T QuotaNonPagedPoolUsage;
  SIZE_T PagefileUsage;
  SIZE_T PeakPagefileUsage;
} PROCESS_MEMORY_COUNTERS;

typedef struct _PROCESS_MEMORY_COUNTERS_EX {
  DWORD  cb;
  DWORD  PageFaultCount;
  SIZE_T PeakWorkingSetSize;
  SIZE_T WorkingSetSize;
  SIZE_T QuotaPeakPagedPoolUsage;
  SIZE_T QuotaPagedPoolUsage;
  SIZE_T QuotaPeakNonPagedPoolUsage;
  SIZE_T QuotaNonPagedPoolUsage;
  SIZE_T PagefileUsage;
  SIZE_T PeakPagefileUsage;
  SIZE_T PrivateUsage;
} PROCESS_MEMORY_COUNTERS_EX;

如您所见， PROCESS_MEMORY_COUNTERS_EX 继承自" PROCESS_MEMORY_COUNTERS -前者以后者的确切定义开头，并添加一个附加字段.

As you can see, PROCESS_MEMORY_COUNTERS_EX "inherits from" PROCESS_MEMORY_COUNTERS - the former starts with the exact definition of the latter, and adds an additional field.

考虑一个功能:

BOOL GetProcessMemoryInfo(
  HANDLE                   Process,
  PPROCESS_MEMORY_COUNTERS ppsmemCounters,
  DWORD                    cb
);

如您所见，它需要一个 PPROCESS_MEMORY_COUNTERS .但是我想将其传递给 PROCESS_MEMORY_COUNTERS_EX 的指针.

As you can see, it takes a PPROCESS_MEMORY_COUNTERS. However I would like to pass it a pointer to a PROCESS_MEMORY_COUNTERS_EX.

根据标准，如果我错了，请纠正我，我应该能够将 PROCESS_MEMORY_COUNTERS_EX * 强制转换为 PPROCESS_MEMORY_COUNTERS * ，因为前者以后者的确切定义.

According to the standard, correct me if I'm wrong, I should be able to cast a PROCESS_MEMORY_COUNTERS_EX* to a PPROCESS_MEMORY_COUNTERS*, since the former starts with the exact definition of the latter.

在C语言中将这样完成:

In C it would be done like so:

PROCESS_MEMORY_COUNTERS_EX pmc;
GetProcessMemoryInfo(process, (PROCESS_MEMORY_COUNTERS*) &pmc, sizeof(pmc));

如果有的话，用C ++代码执行此操作的正确方法是什么?我应该使用 reinterpret_cast< PROCESS_MEMORY_COUNTERS *>(& pmc)， static_cast< PROCESS_MEMORY_COUNTERS *>(& pmc)还是其他方式?

What is the correct way to do this in C++ code, if any? Should I use reinterpret_cast<PROCESS_MEMORY_COUNTERS*>(&pmc), static_cast<PROCESS_MEMORY_COUNTERS*>(&pmc), or something else?

推荐答案

文档说明 GetProcessMemoryInfo 接受

指向PROCESS_MEMORY_COUNTERS或PROCESS_MEMORY_COUNTERS_EX结构的指针，该结构接收有关进程的内存使用情况的信息.

A pointer to the PROCESS_MEMORY_COUNTERS or PROCESS_MEMORY_COUNTERS_EX structure that receives information about the memory usage of the process.

因此， reinterpret_cast< PROCESS_MEMORY_COUNTERS *>(& pmc)将是您的问题的答案.

So, reinterpret_cast<PROCESS_MEMORY_COUNTERS*>(&pmc) would be the answer to your question.

但是您必须将 cb 设置为要传递的对象的大小.

But you must set cb to the size of object being passed.

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