Question

我的目标是声明一个空的2D数组，然后将其初始化，然后在每次do（）运行时都填充值。问题是即使初始化数组，我也会得到nil指针取消引用。

这是我要在服务器模拟器上尝试完成的简单版本。

package main

import "fmt"


type Srv struct {
    A *[][]int
}

func (s Srv) init() {
    arr := make([][]int, 0)
    *s.A = arr
}

func main() {
    s := Srv{nil}
    s.init()
    printSlice(*s.A)
    do(s.A)
    do(s.A)


}

func printSlice(s [][]int) {
    fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}

func do(s *[][]int) {
    *s = append(*s, make([]int, 0))
    printSlice(*s)

    (*s)[0] = append((*s)[0], 5)
    (*s)[0] = append((*s)[0], 6)

    *s = append(*s, make([]int, 0))
    printSlice(*s)
}

我希望得到类似[[5 6 5 6] [] [] []]的输出，但是我得到了nil指针取消引用。

Answer 1

在init执行import numpy as np import cv2 from matplotlib import pyplot as plt MIN_MATCH_COUNT = 10 img1 = cv2.imread('box.png',0) # queryImage img2 = cv2.imread('box_in_scene.png',0) # trainImage # Initiate SIFT detector sift = cv.xfeatures2d.SIFT_create() # find the keypoints and descriptors with SIFT kp1, des1 = sift.detectAndCompute(img1,None) kp2, des2 = sift.detectAndCompute(img2,None) FLANN_INDEX_KDTREE = 0 index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5) search_params = dict(checks = 50) flann = cv2.FlannBasedMatcher(index_params, search_params) matches = flann.knnMatch(des1,des2,k=2) matchesMask = [[0,0] for i in range(len(matches))] # ratio test as per Lowe's paper for i,(m,n) in enumerate(matches): if m.distance < 0.2*n.distance: matchesMask[i]=[1,0] draw_params = dict(matchColor = (0,255,0), singlePointColor = (255,0,0), matchesMask = matchesMask, flags = 0) img3 = cv.drawMatchesKnn(img1,kp1,img2,kp2,matches,None,**draw_params) plt.figure(1234) plt.imshow(img3)的地方，它取消引用了nil指针。 *s.A =尚未初始化（即s.A），而nil是解除引用运算符。但这只是一个问题，因为它在一开始就不必要地复杂。应该是：

甚至在初始化的情况下也可以取消对空指针的引用

1 个答案: