C++ 使用自由函数作为LPOVELAPPED_完成_例程

我无法理解以下编译错误：

unsigned char buf[1000];
const DWORD maxBytes = 1000;
OVERLAPPED o;

void foo(DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, LPOVERLAPPED lpOverlapped) {
  return;
}

void bar(HANDLE hFile) {
  auto lambda_foo = [](DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, LPOVERLAPPED lpOverlapped){return;};
  ReadFileEx(hFile, buf, 1000, &o, lambdafoo); //compiles
  ReadFileEx(hFile, buf, 1000, &o, foo); //doesn't compile
}

错误是“无法将参数5从'void（uu cdecl*）DWORD，DWORD，LPOVERLAPPED'转换为'LPOVERLAPPED'完成程序'”。我使用MSVC2015

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谁能告诉我我做错了什么？为什么它使用lambda编译，而不是使用相同的自由函数

windows中的回调对调用约定有特殊要求。Windows提供了一个名为

CALLBACK

的方便宏，用于在定义函数时指定调用约定

void CALLBACK foo(DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, LPOVERLAPPED lpOverlapped)
{
  return;
}

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windows中的回调对调用约定有特殊要求。Windows提供了一个名为

CALLBACK

的方便宏，用于在定义函数时指定调用约定

void CALLBACK foo(DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, LPOVERLAPPED lpOverlapped)
{
  return;
}