如何改变类型的要素在C++的提升多数组?

0

的问题

我收到一个矩阵和因素的类型 unsigned char 从另一个功能和我试图找到其最大价值。

boost::multi_array<unsigned char, 2> matrix;

所有的元素都是整数,因此我希望重新拟订矩阵类型<int,2>然后执行std::max_element()操作的,但不能确定如何改类型的提升多数组。

boost c++
2021-11-21 09:26:22
1

最好的答案

1

你不需要,使用 max_element. char 是一个整体型,就像 int:

生活在编译器Explorer

#include <boost/multi_array.hpp>
#include <fmt/ranges.h>
#include <algorithm>

int main() {
    using boost::extents;
    boost::multi_array<unsigned char, 2> matrix(extents[10][5]);

    std::iota(         //
        matrix.data(), //
        matrix.data() + matrix.num_elements(), '\x30');

    fmt::print("matrix: {}\n", matrix);

    auto [a, b] = std::minmax_element(matrix.data(),
                                    matrix.data() + matrix.num_elements());

    // as integers
    fmt::print("min: {}, max {}\n", *a, *b);
    // as characters
    fmt::print("min: '{:c}', max '{:c}'\n", *a, *b);
}

程序stdout

matrix: {{48, 49, 50, 51, 52}, {53, 54, 55, 56, 57}, {58, 59, 60, 61, 62}, {63, 64, 65, 66, 67}, {68, 69, 70, 71, 72}, {73, 74, 75, 76, 77}, {78, 79, 80, 81, 82}, {83, 84, 85, 86, 87}, {88, 89, 90, 91, 92}, {93, 94, 95, 96, 97}}
min: 48, max 97
min: '0', max 'a'

图重新诠释

如果你必须(其他原因腋臭使用 max_element)你 可以 使用 multi_array_ref:

// reinterpreting view:
boost::multi_array_ref<const char, 2> view(
    reinterpret_cast<const char*>(matrix.data()),
    std::vector(matrix.shape(), matrix.shape() + 2));

fmt::print("view: {}\n", view);

这印花 生活在编译器Explorer

view: {{'0', '1', '2', '3', '4'}, {'5', '6', '7', '8', '9'}, {':', ';', '<', '=', '>'}, {'?', '@', 'A', 'B', 'C'}, {'D', 'E', 'F', 'G', 'H'}, {'I', 'J', 'K', 'L', 'M'}, {'N', 'O', 'P', 'Q', 'R'}, {'S', 'T', 'U', 'V', 'W'}, {'X', 'Y', 'Z', '[', '\'}, {']', '^', '_', '`', 'a'}}

你还可以重塑它:

view.reshape(std::vector{25, 2});
fmt::print("reshaped: {}\n", view);

reshaped: {{'0', '1'}, {'2', '3'}, {'4', '5'}, {'6', '7'}, {'8', '9'}, {':', ';'}, {'<', '='}, {'>', '?'}, {'@', 'A'}, {'B', 'C'}, {'D', 'E'}, {'F', 'G'}, {'H', 'I'}, {'J', 'K'}, {'L', 'M'}, {'N', 'O'}, {'P', 'Q'}, {'R', 'S'}, {'T', 'U'}, {'V', 'W'}, {'X', 'Y'}, {'Z', '['}, {'\', ']'}, {'^', '_'}, {'`', 'a'}}
2021-11-21 13:34:12

添加文字的问题的答案如要求只是良好的措施
sehe

和这里的一切都没有使用libfmt,只是使用法师为输出: coliru.stacked-crooked.com/a/d36a83decb67d92b (很可怕,对:))
sehe

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