C 二维数组调试¶

一维数组¶

一维数组在调试器中是可以直接显示的本质上变量x是一个指针指向数组对应的第一个元素

/* 输入一个一维数组 从低到高排序 */

#include <stdio.h>

#define DEBUG  // 不希望有自己debug的输出语句把这一行注释掉

#ifdef DEBUG
void printArray(int *x, int N) {
  printf("Array: ");
  for (int i = 0; i < N; i++) {
    printf("%d ", x[i]);
  }
  printf("\n");
}
#endif

int main() {
  freopen("./input.txt", "r", stdin);
  // input.txt
  // 6
  // 6 5 4 3 2 1

  int N = 0;
  printf("请输入数组长度: ");
  scanf("%d", &N);
  printf("\n");

  int x[N];
  // 输入
  for (int i = 0; i < N; i++) {
    printf("请输入第%d个元素的值: ", i);
    scanf("%d", &x[i]);
    printf("\n");
  }

  printf("开始排序\n");
  for (int epoch = 0; epoch < N; epoch++) {
    for (int i = 0; i < N - 1 - epoch; i++) {
      if (x[i] > x[i + 1]) {
        int temp = x[i];
        x[i] = x[i + 1];
        x[i + 1] = temp;
      }
#ifdef DEBUG
      printArray(x, N);
#endif
    }
  }
}

Output:

请输入数组长度: 
请输入第0个元素的值: 
请输入第1个元素的值: 
请输入第2个元素的值: 
请输入第3个元素的值: 
请输入第4个元素的值: 
请输入第5个元素的值: 
开始排序
Array: 5 6 4 3 2 1 
Array: 5 4 6 3 2 1 
Array: 5 4 3 6 2 1 
Array: 5 4 3 2 6 1 
Array: 5 4 3 2 1 6 
Array: 4 5 3 2 1 6 
Array: 4 3 5 2 1 6 
Array: 4 3 2 5 1 6 
Array: 4 3 2 1 5 6 
Array: 3 4 2 1 5 6 
Array: 3 2 4 1 5 6 
Array: 3 2 1 4 5 6 
Array: 2 3 1 4 5 6 
Array: 2 1 3 4 5 6 
Array: 1 2 3 4 5 6

二维数组¶

二维数组具体实现我并不清楚以前好像说过要尽量避免使用二维数组坑比较多

一定要用的话，传参可以通过如下两种比较直观的方式

/* 打印二维数组 */

#include <stdio.h>

// 将二维数组转换为一维传入即可
void printMatrix1(int *A, int r, int c) {
  for (int i = 0; i <= r - 1; i++) {
    for (int j = 0; j <= c - 1; j++) {
      printf("%d ", A[i * c + j]);
    }
    printf("\n");
  }
}

// 按照符合直觉的二维数组传入参数 C99开始支持
void printMatrix2(int r, int c, int A[r][c]) {
  for (int i = 0; i <= r - 1; i++) {
    for (int j = 0; j <= c - 1; j++) {
      printf("%d ", A[i][j]);
    }
    printf("\n");
  }
}

int main() {
  int r = 3;
  int c = 4;
  int A[r][c];
  for (int i = 0; i <= r - 1; i++) {
    for (int j = 0; j <= c - 1; j++) {
      A[i][j] = i * c + j;
    }
  }

  printf("printMatrix1()\n");
  printMatrix1(*A, r, c);
  printf("printMatrix2()\n");
  printMatrix2(r, c, A);
}

Output:

printMatrix1()
0 1 2 3 
4 5 6 7 
8 9 10 11 
printMatrix2()
0 1 2 3 
4 5 6 7 
8 9 10 11

调试二维数组¶

二维数组本质上也是一个指针指向数组第一行的第一个元素但是可能由于编译器编译时去掉了长度信息（或者本来就没有）所以需要在调试时手动指定如何读取该指针处的结构体

在这个例子里面使用 *(int(*)[3][4])A 这样的表达式来做一次转换就可以了

Xcode > 调试开始后的变量窗口 > 右键 > Add Expression...
VS Code > 调试开始后的变量窗口下方的Watch窗口 > 加号

lldb调试过程¶

(lldb) breakpoint set -f test.c -l 34
Breakpoint 1: where = hello-debug`main + 232 at test.c:35:3, address = 0x0000000100003ed8
(lldb) run
Process 46066 launched: '/Users/yangxijie/Downloads/__TEMP/C-debug-try/build/hello-debug' (x86_64)
Process 46066 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100003ed8 hello-debug`main at test.c:35:3
   32       }
   33     }
   34  
-> 35     printf("printMatrix1()\n");
   36     printMatrix1(*A, r, c);
   37     printf("printMatrix2()\n");
   38     printMatrix2(r, c, A);
Target 0: (hello-debug) stopped.
(lldb) frame variable
(int) r = 3
(int) c = 4
(int [][]) A = ([0] = int [] @ 0x00007ff7bfeff280, [1] = int [] @ 0x00007ff7bfeff284, [2] = int [] @ 0x00007ff7bfeff288, [3] = int [] @ 0x00007ff7bfeff28c)
(lldb) frame variable A
(int [][]) A = ([0] = int [] @ 0x00007ff7bfeff280, [1] = int [] @ 0x00007ff7bfeff284, [2] = int [] @ 0x00007ff7bfeff288, [3] = int [] @ 0x00007ff7bfeff28c)
(lldb) expr *(int(*)[3])A
(int [3]) $0 = ([0] = 0, [1] = 1, [2] = 2)
(lldb) expr *(int(*)[8])A
(int [8]) $1 = ([0] = 0, [1] = 1, [2] = 2, [3] = 3, [4] = 4, [5] = 5, [6] = 6, [7] = 7)
(lldb) expr *(int(*)[12])A
(int [12]) $2 = ([0] = 0, [1] = 1, [2] = 2, [3] = 3, [4] = 4, [5] = 5, [6] = 6, [7] = 7, [8] = 8, [9] = 9, [10] = 10, [11] = 11)
(lldb) expr *(int(*)[3][4])A
(int [3][4]) $3 = {
  [0] = ([0] = 0, [1] = 1, [2] = 2, [3] = 3)
  [1] = ([0] = 4, [1] = 5, [2] = 6, [3] = 7)
  [2] = ([0] = 8, [1] = 9, [2] = 10, [3] = 11)
}

可以看到用 frame variable A 只能看到第一行的数据，我们需要手动通过表达式做转化

References¶

https://blog.csdn.net/weixin_42033845/article/details/107921889
https://blog.csdn.net/Kobe51920/article/details/90739757
https://github.com/Microsoft/vscode-cpptools/issues/172#issuecomment-280520910
https://lldb.llvm.org/use/tutorial.html
https://github.com/Yang-Xijie/C-Makefile-template