我一直在测试auto关键字，发现对我来说很奇怪。每个字母占用1个字节（字符类型），并且使用自动说明符，无论如何（我没有测试很长的字符串），auto变量的大小均为4个字节。怎么解释？
char carray[] = "Some test output";
auto variable = "Some test output";
cout<<"carray: "<<sizeof(carray)<<endl;
cout<<"auto: "<<sizeof(variable);
答案 0 :(得分：4)
由于数组到指针的衰减，import numpy as np
import cv2
from utils import CFEVideoConf, image_resize
cap = cv2.VideoCapture(0)
save_path = 'saved-media/watermark.mp4'
frames_per_seconds = 24
config = CFEVideoConf(cap, filepath=save_path, res='720p')
out = cv2.VideoWriter(save_path, config.video_type, frames_per_seconds, config.dims)
img_path = 'images/logo/cfe-coffee.png'
logo = cv2.imread(img_path, -1)
watermark = image_resize(logo, height=50)
#watermark = cv2.cvtColor(watermark, cv2.COLOR_BGR2GRAY)
#watermark = cv2.cvtColor(watermark, cv2.COLOR_GRAY2BGR)
watermark = cv2.cvtColor(watermark, cv2.COLOR_BGR2BGRA)
# grayscale watermark
# cv2.imshow('watermark', watermark)
#print(watermark.shape)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# print(frame[50, 150]) # numpy array
# start_cord_x = 50
# start_cord_y = 150
# color = (255, 0, 0) #BGR 0-255
# stroke = 2
# w = 100
# h = 200
# end_cord_x = start_cord_x + w
# end_cord_y = start_cord_y + h
# cv2.rectangle(frame, (start_cord_x, start_cord_y), (end_cord_x, end_cord_y), color, stroke)
# print(frame[start_cord_x:end_cord_x, start_cord_y:end_cord_y])
frame_h, frame_w, frame_c = frame.shape
#print(frame.shape)
# overlay with 4 channels BGR and Alpha
overlay = np.zeros((frame_h, frame_w, 4), dtype='uint8')
#overlay[100:250, 100:125] = (255, 255, 0, 1) # B, G, R, A
#overlay[100:250, 150:255] = (0, 255, 0, 1) # B, G, R, A
#overlay[start_y:end_y, start_x:end_x] = (B, G, R, A)
#cv2.imshow("overlay", overlay)
watermark_h, watermark_w, watermark_c = watermark.shape
for i in range(0, watermark_h):
for j in range(0, watermark_w):
#print(watermark[i,j])
if watermark[i,j][3] != 0:
#watermark[i, j] # RBGA
offset = 10
h_offset = frame_h - watermark_h - offset
w_offset = frame_w - watermark_w - offset
overlay[h_offset + i, w_offset+ j] = watermark[i,j]
cv2.addWeighted(overlay, 0.25, frame, 1.0, 0, frame)
#frame.addimage(watermark)
frame = cv2.cvtColor(frame, cv2.COLOR_BGRA2BGR)
out.write(frame)
# Display the resulting frame
cv2.imshow('frame',frame)
if cv2.waitKey(20) & 0xFF == ord('q'):
break
# When everything done, release the capture
cap.release()
out.release()
cv2.destroyAllWindows()
变成了variable（大小为4，这对我来说有点令人惊讶-您的平台是什么？）。
如果您希望const char*保留字符数组，则可以使用variable，例如
decltype(auto)答案 1 :(得分：1)
auto variable = "Some test output";
这声明了一个指向字符的指针。该大小将与机器字的大小相同（在32位计算机上为4个字节，在64位计算机上通常为8个字节）。