如何以连续的方式使用一个 malloc 分配 3D、4D、5D 数组并访问各个项目?
像这样:
int* array = malloc(sizeof(int) * width * height);
int item = array[x + y * width];
最佳答案
正如这里的回答( Setting pointer to arbitrary dimension array? ):
特别看 computeIndex
/computeIndexes
。
#include <cstddef>
#include <vector>
template <typename T>
class MultiArray
{
public:
explicit MultiArray(const std::vector<size_t>& dimensions) :
dimensions(dimensions),
values(computeTotalSize(dimensions))
{
assert(!dimensions.empty());
assert(!values.empty());
}
const T& get(const std::vector<size_t>& indexes) const
{
return values[computeIndex(indexes)];
}
T& get(const std::vector<size_t>& indexes)
{
return values[computeIndex(indexes)];
}
size_t computeIndex(const std::vector<size_t>& indexes) const
{
assert(indexes.size() == dimensions.size());
size_t index = 0;
size_t mul = 1;
for (size_t i = 0; i != dimensions.size(); ++i) {
assert(indexes[i] < dimensions[i]);
index += indexes[i] * mul;
mul *= dimensions[i];
}
assert(index < values.size());
return index;
}
std::vector<size_t> computeIndexes(size_t index) const
{
assert(index < values.size());
std::vector<size_t> res(dimensions.size());
size_t mul = values.size();
for (size_t i = dimensions.size(); i != 0; --i) {
mul /= dimensions[i - 1];
res[i - 1] = index / mul;
assert(res[i - 1] < dimensions[i - 1]);
index -= res[i - 1] * mul;
}
return res;
}
private:
size_t computeTotalSize(const std::vector<size_t>& dimensions) const
{
size_t totalSize = 1;
for (auto i : dimensions) {
totalSize *= i;
}
return totalSize;
}
private:
std::vector<size_t> dimensions;
std::vector<T> values;
};
int main()
{
MultiArray<int> m({3, 2, 4});
m.get({0, 0, 3}) = 42;
m.get({2, 1, 3}) = 42;
for (size_t i = 0; i != 24; ++i) {
assert(m.computeIndex(m.computeIndexes(i)) == i);
}
}
Demo关于c++ - 如何分配和访问 3D、4D、5D 数组?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/33041606/