C++ 基于模板C+创建转置矩阵函数+；

我正试图使用此创建我的第一个模板，但遇到了一个问题，我不知道如何处理多个嵌套参数：

我创建的原始函数实现如下：

QVector< QVector<double> > transpose(QVector< QVector<double> > &matrix)
{
    int pre_numcols = matrix.size();
    int pre_numrows = matrix[0].size();
    QVector< QVector<double> > transposed(pre_numrows);
    QVector<double> newcols(pre_numcols);
    qFill(newcols.begin(), newcols.end(), 0.0);
    qFill(transposed.begin(), transposed.end(), newcols);
    qDebug()<<transposed.size();
    qDebug()<<transposed[0].size();
    for (int i = 0; i < pre_numcols; ++i)
    {
        for (int j = 0; j < pre_numrows; ++j)
        {
            transposed[j][i] = matrix[i][j];
        }
    }
    return transposed;
}

如果我将

T

读为“container holding container holding some small type”，那么如果

newcols

变量是一个子集，我如何声明它呢

---

注意：稍后我将编辑

qFill（）

部分以适应其他情况，例如

std:：

。

您可以使用模板作为模板参数：

template <
    template <typename> class Container,
    typename ValueType
>
void foo(Container<ValueType> const & c);

因此，我们必须将函数改为

template <
    template <typename, typename> class C,
    typename T,
    template <typename> class A = std::allocator,
    typename InnerType = C< T, A<T> >,
    typename OuterType = C< InnerType, A<InnerType> >
>
OuterType transpose(OuterType & matrix)
{
    int pre_numcols = matrix.size();
    int pre_numrows = matrix[0].size();
    OuterType transposed(pre_numrows);
    InnerType newcols(pre_numcols);
    // ...
    return transposed;
}

---

您可以看到它在这里工作：

C++11是您的一个选项吗？@nijansen是的，它是一个选项。@Duality又添加了一个解决方案，我想我现在继续：PHah，谢谢您的努力。您已经达到了今天的

配额：P

template <
    template <typename> class Container,
    typename ValueType
>
Container< Container<ValueType> > transpose(Container< Container<ValueType> > & matrix)
{
    int pre_numcols = matrix.size();
    int pre_numrows = matrix[0].size();
    Container< Container<ValueType> > transposed(pre_numrows);
    Container<ValueType> newcols(pre_numcols);
    // ...
    return transposed;
}

template <
    typename T,
    typename Allocator = allocator<T>
>
class vector

template <
    template <typename, typename> class C,
    typename T,
    template <typename> class A = std::allocator,
    typename InnerType = C< T, A<T> >,
    typename OuterType = C< InnerType, A<InnerType> >
>
OuterType transpose(OuterType & matrix)
{
    int pre_numcols = matrix.size();
    int pre_numrows = matrix[0].size();
    OuterType transposed(pre_numrows);
    InnerType newcols(pre_numcols);
    // ...
    return transposed;
}

template <typename T> using vector = std::vector<T, std::allocator<T>>;
vector<vector<int>> v;
auto vprime = transpose<vector>(v);

namespace
{
    template <typename T> struct get_inner_i {};

    template <template <typename> class T, typename Inner> 
    struct get_inner_i<T<Inner>> { typedef Inner type; };

    template <
        template <typename, typename> class T, 
        typename Inner,
        template <typename> class Allocator
    > struct get_inner_i<T<Inner, Allocator<Inner>>> { typedef Inner type; };

    template <typename T> using get_inner = typename get_inner_i<T>::type;
}

template <typename MatrixType>
MatrixType transpose(MatrixType const & matrix)
{
    auto const nrows = matrix.size();
    auto const ncols = nrows > 0 ? matrix[0].size() : 0;

    MatrixType transposed(ncols, get_inner<MatrixType>(nrows));
    for(auto k = 0; k < nrows; ++k)
        for(auto j = 0; j < ncols; ++j)
            transposed[j][k] = matrix[k][j];

    return transposed;
}

namespace
{
    template <typename Container>
    struct value_type_i
    {
        typedef typename std::decay<
            decltype(*std::begin(std::declval<
                Container const &
            >()))
        >::type type;
    };

    template <typename Container>
    using value_type = typename value_type_i<Container>::type;
}

template <typename MatrixType>
MatrixType transpose(MatrixType const & matrix)
{
    auto const nrows = matrix.size();
    auto const ncols = nrows > 0 ? matrix[0].size() : 0;

    MatrixType transposed(ncols, value_type<MatrixType>(nrows));
    for(auto k = 0; k < nrows; ++k)
        for(auto j = 0; j < ncols; ++j)
            transposed[j][k] = matrix[k][j];

    return transposed;
}