无效操作：类型为*int的索引 golang

huangapple
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英文:

Invalid operation: index of type *int golang

问题

**目标：**我一直在使用Go解决《破解编程面试》一书中的第6题。

注意：我不需要这个问题的帮助或解决方案

给定一个由NxN矩阵表示的图像，图像中的每个像素占据4个字节，编写一个方法将图像旋转90度。你能原地完成吗？

**问题：**我创建了一个数组的数组来表示矩阵，并创建了一个交换函数来顺时针交换矩阵中的元素。但是出现了一个非常奇怪的错误，当我尝试编译时：

  1. ./Q6.go:29: invalid operation: b[N - col - 1] (index of type *int)
  2. ./Q6.go:30: invalid operation: b[N - row - 1] (index of type *int)

我从哪里得到了类型为int的索引？在Go文档中，len(v)返回类型为int，而其他所有值都是类型为'int'的，那么我是如何得到类型为int的索引的？

代码：

  1. package main
  3. import "fmt"
  5. func main() {
  6.     b := [][]int{{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}} // 4 by 4 array going from 1 to 16
  7.     N := len(b)
  9.     for row := 0; row < N / 2; row++ {
  10.         for col := row; col < N - row - 1; col++ {
  11.             a := &b[row][col]
  12.             b := &b[col][N - row - 1]
  13.             c := &b[N - col - 1][col] // <-- 错误在这里
  14.             d := &b[N - row - 1][N - col - 1] // <-- 错误在这里
  15.             fourSwap(a, b, c, d)
  16.         }
  17.     }
  19.     for r := range b {
  20.         for c:= range b[0] {
  21.             fmt.Print(b[r][c])
  22.         }
  23.         fmt.Print("\n")
  24.     }
  25.         
  26. }
  28. // [a][-][-][b]        [c][-][-][a]
  29. // [-][-][-][-] -->    [-][-][-][-]
  30. // [-][-][-][-] -->    [-][-][-][-]
  31. // [c][-][-][d]        [d][-][-][b]
  33. func fourSwap(a, b, c, d *int) {
  34.     temp := *b
  35.     *b = *a
  36.     *a = *c
  37.     *c = *d
  38.     *d = temp
  39. }
英文:

Objective: I have been solving question 6 from the book 'Cracking the Coding interview' by using Go.

NOTE I DO NOT WAN'T HELP OR SOLUTIONS TO THIS QUESTION

Given an image represented by an NxN matrix, where each pixel in the image is 4
bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

Problem: I made an array of arrays to represent the matrix and I created a swap function to swap the elements clockwise in the matrix. For some reason I get this really weird error when trying to compile:

  1. ./Q6.go:29: invalid operation: b[N - col - 1] (index of type *int)
  2. ./Q6.go:30: invalid operation: b[N - row - 1] (index of type *int)

Where am I getting type *int as an index? In the Go documenation, len(v) returns type int and everything else is in the value of 'N - col - 1' is type int so how am I getting type *int index?

Code:

  1. package main
  3. import &quot;fmt&quot;
  5. func main() {
  6. 	b := [][]int{{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}} // 4 by 4 array going from 1 to 16
  7. 	N := len(b)
  9. 	for row := 0; row &lt; N / 2; row++ {
  10. 		for col := row; col &lt; N - row - 1; col++ {
  11. 			a := &amp;b[row][col]
  12. 			b := &amp;b[col][N - row - 1]
  13. 			c := &amp;b[N - col - 1][col] // &lt;-- Error here
  14. 			d := &amp;b[N - row - 1][N - col - 1] // &lt;-- Error here
  15. 			fourSwap(a, b, c, d)
  16. 		}
  17. 	}
  19. 	for r := range b {
  20. 		for c:= range b[0] {
  21. 			fmt.Print(b[r][c])
  22. 		}
  23. 		fmt.Print(&quot;\n&quot;)
  24. 	}
  25. 		
  26. }
  28. // [a][-][-][b]		[c][-][-][a]
  29. // [-][-][-][-] --&gt; [-][-][-][-]
  30. // [-][-][-][-]	--&gt; [-][-][-][-]
  31. // [c][-][-][d]		[d][-][-][b]
  33. func fourSwap(a, b, c, d *int) {
  34. 	temp := *b
  35. 	*b = *a
  36. 	*a = *c
  37. 	*c = *d
  38. 	*d = temp
  39. }

答案1

得分: 2

你在循环内部声明了b，这就遮蔽了你的切片。

  1. for row := 0; row < N / 2; row++ {
  2.     for col := row; col < N - row - 1; col++ {
  3.         a := &b[row][col]
  4.         b := &b[col][N - row - 1] <<< b现在是一个*int
  5.         c := &b[N - col - 1][col] // <-- 这里有错误
  6.         d := &b[N - row - 1][N - col - 1] // <-- 这里有错误
  7.         fourSwap(a, b, c, d)
  8.     }
  9. }
英文:

You declare b inside the loop, and that shadows your slice.

  1. for row := 0; row &lt; N / 2; row++ {
  2.     for col := row; col &lt; N - row - 1; col++ {
  3.         a := &amp;b[row][col]
  4.         b := &amp;b[col][N - row - 1] &lt;&lt;&lt;&lt; b is now an *int
  5.         c := &amp;b[N - col - 1][col] // &lt;-- Error here
  6.         d := &amp;b[N - row - 1][N - col - 1] // &lt;-- Error here
  7.         fourSwap(a, b, c, d)
  8.     }
  9. }

答案2

得分: 1

你在出错的那一行之前创建了一个新的本地变量b，它是一个指针：

  1. b := &b[col][N - row - 1]
英文:

You are creating a new local variable b which is a pointer on the line before you get the error:

  1. b := &amp;b[col][N - row - 1]

huangapple
  • 本文由 发表于 2015年5月1日 12:44:33
  • 转载请务必保留本文链接：https://go.coder-hub.com/29981710.html
  • arrays
  • go
  • indexing
  • pointers
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