如何修改传递给函数的二维数组？

Why does the following code give me a segmentation fault?

为什么以下代码会给我一个分段错误?

#define MAXROWS 10
#define MAXCOLS 10
void getInput (int *data[MAXROWS][MAXCOLS]) {
  int rows, cols;
  int curRow, curCol;
  printf ("How many rows and cols?");
  scanf ("%d %d", rows, cols);

  for (curRow = 0; curRow < rows; curRow++) {
    for (curCol = 0; curCol < cols; curCol++) {
      scanf ("%d", data[curRow][curCol]);
      printf ("%d\n", *data[curRow][curCol]);
    }
  }
}

void main () {
  int data[MAXROWS][MAXCOLS];

  getInput (data);
}

It seems to be that the scanf and printf statements aren't getting the right data type passed in, but I can't work out what they should be.

似乎scanf和printf语句没有传入正确的数据类型,但我无法弄清楚它们应该是什么。

How can I change it so that it works properly?

如何更改它以使其正常工作?

3 个解决方案

#1

This declares an array of MAXROWS arrays of pointers to int.

这声明了一个指向int的MAXROWS指针数组。

int *data[MAXROWS][MAXCOLS];

However, in a function definition, top level arrays (of any size) are equivalent to pointers because arrays always decay to pointers to the type of the array member on passing to a function.

但是,在函数定义中,*数组(任何大小)都等效于指针,因为数组在传递给函数时总是衰减到指向数组成员类型的指针。

So your function definition is equivalent to:

所以你的函数定义相当于:

void getInput (int *(*data)[MAXCOLS])

i.e. a pointer to an array of MAXCOLS pointers to int.

即指向指向int的MAXCOLS指针数组的指针。

As your code stands, you never initialize any of the int pointers in the array, as you are passing a 2d array of ints as a pointer to a 2d array of int *.

正如你的代码所代表的那样,你永远不会初始化数组中的任何int指针,因为你传递了一个2d数组的int作为指向int *的2d数组的指针。

What you probably want to pass, is a pointer to an array of MAXCOLS int:

您可能想要传递的是指向MAXCOLS int数组的指针:

void getInput (int (*data)[MAXCOLS])

or equivalently:

void getInput (int data[][MAXCOLS])

Then you do the following:

然后执行以下操作:

int main(void)
{
    int data[MAXROWS][MAXCOLS];

    getInput(data);

    return 0;
}

You are then passing your 2d array as a pointer to its first element (a pointer to a row or an array of MAXCOLS ints).

然后,您将2d数组作为指向其第一个元素的指针(指向行或MAXCOLS整数数组的指针)。

If you make sure change be sure to change:

如果您确保更改,请务必更改:

  scanf ("%d", data[curRow][curCol]);
  printf ("%d\n", *data[curRow][curCol]);

to:

  scanf ("%d", &data[curRow][curCol]);
  printf ("%d\n", data[curRow][curCol]);

Also, check your parameters here:

另外,请在此处检查您的参数:

scanf ("%d %d", &rows, &cols);

You need to be passing pointers to rows and cols.

您需要将指针传递给行和列。

Make sure to add some bounds checking to your input function so that you don't attempt to read more rows and columns than MAXROWS or MAXCOLS.

确保在输入函数中添加一些边界检查,这样您就不会尝试读取比MAXROWS或MAXCOLS更多的行和列。

#2

scanf accepts address of variables, not the content of it:

scanf接受变量的地址,而不是它的内容:

void getInput (int data[][MAXCOLS]) {
  int rows, cols;
  int curRow, curCol;
  printf ("How many rows and cols?");
  scanf ("%d %d", &rows, &cols);
  //scanf ("%d %d", &rows, &cols);
  for (curRow = 0; curRow < rows; curRow++) {
    for (curCol = 0; curCol < cols; curCol++) {
          scanf ("%d", &data[curRow][curCol]);
          printf ("%d\n", data[curRow][curCol]);
        }
    }
}

#3

There were a few different problems.

有几个不同的问题。

First, when passing arrays to functions you only need the definition of N-1 dimensions. For example if you're passing a 3D array you would put the size of the last 2 dimensions in the function sig and leave the first one empty.

首先,将数组传递给函数时,只需要定义N-1维。例如,如果您传递3D数组,则将最后2个维度的大小放在函数sig中,并将第一个维度留空。

foo(int threeD[][10][15]);

Second, scanf takes the address of the argument, which for your array looks like this

其次,scanf获取参数的地址,对于您的数组看起来像这样

&data[curRow][curCol]

Third, you should always check the range of you input to make sure it's valid:

第三,你应该经常检查你输入的范围,以确保它是有效的:

  if (rows > MAXROWS || cols > MAXCOLS) {
    printf("Bad array dimensions\n");
    return;
  }

Fourth, always compile with all warnings turned on - the compiler will warn you about allot of these things:

第四,总是在打开所有警告的情况下编译 - 编译器会警告你有关这些事情:

gcc -Wall pass_array.c -o pass_array

#include <stdio.h>

#define MAXROWS 10
#define MAXCOLS 10

void getInput (int data[][MAXCOLS]) {
  int rows, cols;
  int curRow, curCol;
  printf ("How many rows and cols?");
  scanf ("%d %d", &rows, &cols);

  if (rows > MAXROWS || cols > MAXCOLS) {
    printf("Bad array dimensions\n");
    return;
  }

  for (curRow = 0; curRow < rows; curRow++) {
    for (curCol = 0; curCol < cols; curCol++) {
      scanf ("%d", &data[curRow][curCol]);
      printf ("%d\n", data[curRow][curCol]);
    }
  }
}

int main () {
  int data[MAXROWS][MAXCOLS];

  getInput (data);
    return 0;
}

#1