Question

class A
{
    ...
    B b;
}

我传入的unique_ptr什么时候被删除？

void A::SetB( unique_ptr<B> b )
{
    this->b = *b;
} // At end of scope, is `b` now reset 
  // and the `B b` in class `A` just stores the value in it?

如果上面的答案是否定的，那么它就不会被删除......这会将其删除：

void A::SetB( unique_ptr<B> b )
{
    this->b = *move(b);
} // At end of scope, is `b` now reset
  // and the `B b` in class `A` just stores the value in it?

或者我必须自己重置它，如果我希望在那时删除它：

void A::SetB( unique_ptr<B> b )
{
    this->b = *b;
    b.reset();
}

Answer 1

在前两种情况下，unique_ptr在函数SetB返回时被重置。在任何一种情况下你都不会泄漏任何内存，但你所做的事情很奇怪。

在第一种情况下

this->b = *b;

unique_ptr::operator*返回对托管对象的引用。因此，您需要将B参数中包含的unique_ptr<B>实例分配给您的班级数据成员b。

第二种情况

this->b = *move(b);

的行为与第一个完全相同。这次你所做的就是unique_ptr::operator*上的unique_ptr<B>&&调用unique_ptr只是将其参数转换为右值参考。

在这两种情况下，B参数保留最初调用的SetB实例unique_ptr的所有权，并且当函数返回时它将销毁它。

您的用例似乎不是您应该使用void A::SetB( B b ) { this->b = move(b); }的用例，您只需要一个setter。可能是以下

import cv2
import numpy as np
import zbar
import math
import time


#width of the object
qrwcoord = 0
qrPL = 0
qrNorm = 0
box = 0
focalLenght = 608 #Calibration data
intrinsic = np.array([[608.14578, 0, 292.31368], [0, 608.82584, 261.47420], [0, 0, 1]])  #3x3 Calibration intrinsic matrix
distortion = np.array([ [0.02232355, -0.11265588, 0.00247792, -0.00201052, 0.22786218]]) #1x5 Distortion vector

def distance_to_camera(knownWidth, focalLength, perWidth):
    return (knownWidth * focalLength) / perWidth

def decode_QR(image):
    global box

    gray = cv2.cvtColor(image,cv2.COLOR_RGB2GRAY)
    (height, width)=gray.shape
    raw = str(gray.data)
    scanner = zbar.ImageScanner()
    scanner.parse_config('enable')
    image1 = zbar.Image(width, height, 'Y800', raw)
    scanner.scan(image1)
    for symbol in image1:
        TLC, BLC, BRC, TRC = [item for item in symbol.location]
        box = np.array([[TLC],[TRC],[BRC],[BLC]])
        qrData=symbol.data
        qrStrip = []
        qrStrip = qrData.split(';')
        qrNorm = qrStrip[0] #Qr Code norm vector
        qrPL = qrStrip[1]
        qrwcoord = qrStrip[2] #QR Code World Coordinates
        qrPL=float(qrPL) #Qr Code size in meters

        print 'decoded', symbol.type, 'symbol', '"%s"' % symbol.data
        qrpixelwidth = math.sqrt((TLC[0]-TRC[0])**2+(TLC[1]-TRC[1])**2)
        qrpixelheight = math.sqrt((BLC[0]-BRC[0])**2+(BLC[1]-BRC[1])**2)

        pixel_size = float(qrPL/qrpixelwidth) #Pixel Size in meter
        plane_x_size = float(pixel_size*640)
        plane_y_size = float(pixel_size*480)

        dist = distance_to_camera(qrPL, focalLenght, qrpixelwidth)
        print qrNorm
        print qrPL
        print qrwcoord
        print box
        print qrpixelwidth
        print qrpixelheight
        print "Distance from QR to Camera is:", dist
        print qrStrip
        return box

cv2.namedWindow("Streaming...")
capture = cv2.VideoCapture(0)
capture.open('http://192.168.5.2:8080/stream/video.mjpeg')
while True:
    (grabbed, img) = capture.read()
    if not grabbed:
        break
    box = decode_QR(img)
    cv2.drawContours(img, [box], -1, (0, 255, 0), 2)
    cv2.imshow("Streaming...", img)
    #time.sleep(0.05)
    key = cv2.waitKey(1)& 0xFF
    if key == ord("q"):
        break
cv2.destroyWindow("Streaming...")

unique_ptr何时在此setter上重置？

1 个答案: