C ++对象的快速排序向量 [英] c++ quicksort vector of objects

问题描述

在我的对象向量上使用std :: qsort时遇到麻烦.(请注意，此代码在循环内)

I am having troubles using std::qsort on my vector of objects. (Note that this code is inside a loop)

std::vector<s_GridData> info = GetAllAdjacentObjInfoFromMap(FLOOR_OBJ, e_Object::eObject_WIRE, itr.getPos());

//No wires adjacent!
if (info.size() == 0) {
  continue;
}

std::cout << "Before sorting: ";
std::cout << info;

std::qsort(&info, info.size(), sizeof(s_GridData),
  [](const void *lhs, const void *rhs)->int {
    s_GridData gridLhs = *reinterpret_cast<const s_GridData*>(lhs);
    s_GridData gridRhs = *reinterpret_cast<const s_GridData*>(rhs);
    if (gridLhs.groupID < gridRhs.groupID) return -1;
    if (gridRhs.groupID < gridLhs.groupID) return 1;
    return 0;
  }
);

std::cout << "After sorting: ";
std::cout << info;

在快速排序代码中，似乎该快速排序正在擦除我的 info .Lambda出问题了吗?还是有另一个使用qsort的要求，例如赋值运算符重载.但是 s_GridData 仅仅是整数值的结构.

Here specifically in the quicksort code, it seems that the quicksort is erasing my info. Is there something wrong with the lambda? Or is there another requirement for using qsort like an assignment operator overload. However s_GridData is simply a struct of integral values.

谢谢.

推荐答案

您正在将错误的参数传递给 qsort()(这实际上是C函数，最初不在 namespace std中):

You're passing the wrong arguments to qsort() (which is really a C function not originally in namespace std):

std::qsort(&info, ...

马上就错了，因为 info 是 std :: vector ，但是 qsort()需要C样式的数组.您可以通过以下方式解决它:

Right off the bat that's wrong, because info is a std::vector but qsort() requires a C-style array. You can fix it this way:

std::qsort(info.data(), ...

或在C ++ 11之前:

Or before C++11:

std::qsort(&info[0], ...

但是，更好的解决方案是使用 std :: sort()，这是一种真正的 C ++函数，具有类型安全性和其他优点.它是这样的:

However, the better solution is to use std::sort(), which is a bona fide C++ function giving type safety and other benefits. It goes something like this:

sort(info.begin(), info.end(),
    [](const s_GridData& lhs, const s_GridData& rhs)->bool {
        return gridLhs.groupID < gridRhs.groupID;
    });

如您所见，C ++方式更为简洁，并且如果您的排序适用于所有实例，则可以单独定义(通常是内联自由函数)，在这种情况下:

As you can see, the C++ way is more concise, and if your ordering is applicable across all your instances, you can define it separately (typically as an inline free function), in which case:

sort(info.begin(), info.end());

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