小编Hua*_*ang的帖子

以下是测试代码及其矩阵索引输出.在MATLAB中是不是x(:)和x(1:end)同样的事情？为什么他们的产出不同？

>>x = [1 2 3;4 5 6]
x =
     1     2     3
     4     5     6
>> xx = x(:)
xx =
     1
     4
     2
     5
     3
     6
>> xx = x(1:end)
xx =
     1     4     2     5     3     6

>> fprintf('How about single quote('')?\n')
How about single quote(')?

输出与:

>> fprintf("How about single quote(\')?\n")
How about single quote(')?

这是更通用的理解(逃避字符由反斜杠'\'和字符(例如'n')组成)

那么,反斜杠('\')是否可以通过单引号(')来改变,以表示MATLAB中的转义字符？

我有一个类型为或std::vector的std::variant元素。如果迭代元素的类型为 ，我想遍历这个向量和一个额外的项目。但是，似乎不允许在运行时查询索引。我怎样才能做到这一点？intstd::set<int>insertstd::set<int>

#include <variant>
#include <set>
#include <vector>

int main()
{
    using Variants = std::variant<int, std::set<int>>;

    std::vector<Variants> var_vec;
    var_vec.push_back(999);
    std::set<int> a = {0,1,2};
    var_vec.push_back(a);

    for (int i = 0; i < var_vec.size(); ++i)
    {
        // if the element var_vec[i] is of type std::set<int>
        if (var_vec[i].index() == 1) var_vec[i].insert(888);   // !ERROR! How to achieve this?
    }
    
    return 0;
}

错误信息：

error: '__gnu_cxx::__alloc_traits<std::allocator<std::variant<int, std::set<int, std::less<int>, std::allocator<int> > > >, std::variant<int, std::set<int, std::less<int>, std::allocator<int> > …

我在 main.cpp 中有一个例程，用户将在其中指定要在程序中执行的模式。一旦指定了模式，就会执行相应的块——首先将父求解器向下转换为子求解器，并调用solve子类中的关联方法。

    std::unique_ptr<SudokuSolver> solver;
    if (mode == MODES::SEQUENTIAL_BACKTRACKING) 
    {
        solver = std::make_unique<SudokuSolver_SequentialBacktracking>();
        SudokuSolver_SequentialBacktracking* child_solver = dynamic_cast<SudokuSolver_SequentialBacktracking*>(solver.get());
        child_solver->solve(board);
    } 
    else if (mode == MODES::SEQUENTIAL_BRUTEFORCE)
    {
        solver = std::make_unique<SudokuSolver_SequentialBruteForce>();
        SudokuSolver_SequentialBruteForce* child_solver = dynamic_cast<SudokuSolver_SequentialBruteForce*>(solver.get());
        child_solver->solve(board);
    }   
    else if (mode == MODES::PARALLEL_BRUTEFORCE)
    {
        int NUM_THREADS = (argc >= 5) ? std::stoi(argv[4]) : 2;
        omp_set_num_threads(NUM_THREADS);
        
        #pragma omp parallel
        {
            #pragma omp single nowait
            {
                solver = std::make_unique<SudokuSolver_ParallelBruteForce>();
                SudokuSolver_ParallelBruteForce* child_solver = dynamic_cast<SudokuSolver_ParallelBruteForce*>(solver.get());
                child_solver->solve(board);
            }
        }
    }
    else if (mode == MODES::SEQUENTIAL_DANCINGLINKS)
    {
        solver …