通过引用传递多维数组未知大小 [英] Pass By Reference Multidimensional Array With Unknown Size

问题描述

如何用C或C ++未知大小？

How to pass by reference multidimensional array with unknown size in C or C++?

例如，在主要功能我有：

For example, in main function I have:

int main(){
    int x, y;
    int arr[x][y];
    // pass_by_ref(/* passing just arr[][] by reference */);
}  

和功能：

void pass_by_ref(/* proper parameter for arr[][] */){
    // int size_x_Arr = ???
    // int size_y_arr = ???
}

如何实施注释行？

How to implement the commented line?

推荐答案

简单地说，你不能。在C中，你不能按引用传递，因为C有没有引用。在C ++中，你不能传递数组未知大小，因为C ++不支持可变lenght阵列。

Simply put, you can't. In C, you can't pass by reference, since C has no references. In C++, you can't pass arrays with unknown size, since C++ doesn't support variable-lenght arrays.

替代方案：在C99，传递一个指针变长数组;在C ++中，通过一个参考的std ::矢量＆lt;的std ::矢量＆lt; T＆GT;方式＆gt;

Alternative solutions: in C99, pass a pointer to the variable-length array; in C++, pass a reference to std::vector<std::vector<T>>.

示范为C99：

#include <stdio.h>

void foo(int n, int k, int (*arr)[n][k])
{
    int i, j;
    for (i = 0; i < n; i++) {
        for (j = 0; j < k; j++) {
            printf("%3d ", (*arr)[i][j]);
        }
        printf("\n");
    }
}

int main(int argc, char *argv[])
{
    int a = strtol(argv[1], NULL, 10);
    int b = strtol(argv[2], NULL, 10);

    int arr[a][b];
    int i, j;
    for (i = 0; i < a; i++) {
        for (j = 0; j < b; j++) {
            arr[i][j] = i * j;
        }
    }

    foo(a, b, &arr);

    return 0;
}

示范为C ++ 03：

Demonstration for C++03:

#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>

void foo(std::vector < std::vector < int > > &vec)
{
    for (std::vector < std::vector < int > >::iterator i = vec.begin(); i != vec.end(); i++) {
        for (std::vector<int>::iterator j = i->begin(); j != i->end(); j++) {
            std::cout << *j << " ";
        }
        std::cout << std::endl;
    }
}

int main(int argc, char *argv[])
{
    int i = strtol(argv[1], NULL, 10);
    int j = strtol(argv[2], NULL, 10);

    srand(time(NULL));

    std::vector < std::vector < int > > vec;
    vec.resize(i);
    for (std::vector < std::vector < int > >::iterator it = vec.begin(); it != vec.end(); it++) {
        it->resize(j);
        for (std::vector<int>::iterator jt = it->begin(); jt != it->end(); jt++) {
            *jt = random() % 10;
        }
    }

    foo(vec);

    return 0;
}

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