创建2d数组，一个维在编译时不知道 [英] Creating a 2d array, one dimension not known at compile time

问题描述

我需要澄清两件事：二维数组和长度在运行时确定的数组。第一个长度未知，第二个长度为2个。

Two things going on I need clarification with: two dimensional array and an array whose length is determined at run time. The first length is unknown, the second is known to be two.

char** mapping = new char*[2];//2d array
mapping[2][0] = 'a';

此程序崩溃，因为正在写入的内存未分配给阵列，如何修复它？

This program crashes because of memory being written to that is not allocated to the array, how can I fix it? Could you please explain your answer.

推荐答案

如果只有第一个数组大小是一个运行时间值是编译时值），那么您可以一次性分配它。在你的情况下，对于运行时大小 n

If only the first of the array sizes is a run-time value (and the rest are compile-time values), then you can allocate it in one shot. In your case, for run-time size n

char (*mapping)[2] = new char[n][2];

像往常一样访问此数组，即 mapping [i] j] ，其中 i 位于 0..n-1 范围和 j 在 0..1 范围内。

Access this array "as usual", i.e. as mapping[i][j], where i is in 0..n-1 range and j is in 0..1 range.

除非你有一些具体的效率/布局要求，最好使用 std :: vector 。

However, unless you have some specific efficiency/layout requirements, it might be better idea to use std::vector.

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