小编Gal*_*axy的帖子

我想知道char s[] = "hello"和之间的区别是什么char *s = "hello".

看完这个和这个,我还没有在这个问题上非常清楚.

据我所知,内存中有五个数据段,Text,BSS,Data,Stack和Heap.

根据我的理解,

在以下情况下char s[] = "hello":

1. "hello" 在文本中.

2. s 如果是全局变量,则在Data中;如果是局部变量,则在Stack中.

3. 我们还有一个存储"hello"位置的副本s,因此我们可以修改此字符串的值s.

在以下情况下char *s = "hello":

1. "hello" 在文本中.
2. s 如果是全局变量,则在Data中;如果是局部变量,则在Stack中.
3. s只是指向"hello"Text并且我们没有它的副本,因此通过此指针修改字符串的值应该导致"Segmentation Fault".

我对吗？

当我尝试使用FFmpeg访问网络摄像头时,Mac上出现了一个非常奇怪的问题.例如:

ffmpeg -f avfoundation -i "1" -framerate 60 -vcodec libx264 -preset veryfast -f flv rtmp://localhost:1935/hls/test 

无论我设置什么帧率,错误总是一样的.

[avfoundation @ 0x7ff831800000] Selected framerate (29.970030) is not supported by the device
[avfoundation @ 0x7ff831800000] Supported modes:
[avfoundation @ 0x7ff831800000]   320x240@[120.101366 120.101366]fps
[avfoundation @ 0x7ff831800000]   640x480@[120.101366 120.101366]fps
[avfoundation @ 0x7ff831800000]   800x600@[60.000240 60.000240]fps
[avfoundation @ 0x7ff831800000]   1024x768@[30.000030 30.000030]fps
[avfoundation @ 0x7ff831800000]   1280x720@[60.000240 60.000240]fps
[avfoundation @ 0x7ff831800000]   1280x1024@[30.000030 30.000030]fps
[avfoundation @ 0x7ff831800000]   1920x1080@[30.000030 30.000030]fps
[avfoundation @ 0x7ff831800000]   320x240@[30.000030 30.000030]fps
[avfoundation @ 0x7ff831800000]   640x480@[30.000030 30.000030]fps
[avfoundation @ …

我对AngularJS表达式感到困惑.

从w3schools.com,我了解到了这一点

1. AngularJS表达式可以写在双括号内:{{ expression }}.
2. AngularJS表达式也可以写在指令中: ng-bind="expression".

但为什么我们用ng-src={{...}}而不是ng-src="..."？

ng-src处理AngularJS表达式时是一种特殊情况吗？

我想使用FFmpeg从Mac流式传输我的网络摄像头.

首先,我使用了检查支持的设备 ffmpeg -f avfoundation -list_devices true -i ""

输出:

[AVFoundation input device @ 0x7fdf1bd03000] AVFoundation video devices:
[AVFoundation input device @ 0x7fdf1bd03000] [0] USB 2.0 Camera #2
[AVFoundation input device @ 0x7fdf1bd03000] [1] FaceTime HD Camera
[AVFoundation input device @ 0x7fdf1bd03000] [2] Capture screen 0
[AVFoundation input device @ 0x7fdf1bd03000] [3] Capture screen 1
[AVFoundation input device @ 0x7fdf1bd03000] AVFoundation audio devices:
[AVFoundation input device @ 0x7fdf1bd03000] [0] Built-in Microphone

设备[0]是我想要使用的网络摄像头.

然后我尝试使用捕获网络摄像头 ffmpeg -f avfoundation -i "0" out.mpg

输出: …

当我试图在Ubuntu上链接OpenCV库时,发生了一些我无法理解的问题.

我在Ubuntu 14.04上使用了OpenCV 2.4.11和Qt创建器.

在我的项目文件中,我写道

INCLUDEPATH += /usr/local/include/opencv
INCLUDEPATH += /usr/local/include/opencv2

LIBS += -L/usr/local/lib\
     -lopencv_calib3d\
     -lopencv_contrib\
     -lopencv_core\
     -lopencv_features2d \
     -lopencv_flann\
     -lopencv_gpu\
     -lopencv_highgui\
     -lopencv_imgproc\
     -lopencv_legacy\
     -lopencv_ml\
     -lopencv_nonfree\
     -lopencv_objdetect\
     -lopencv_ocl\
     -lopencv_photo\
     -lopencv_stitching\
     -lopencv_superres\
     -lopencv_ts\
     -lopencv_video\
     -lopencv_videostab

但是在构建项目时存在许多错误,例如undefined reference to 'cvCreateMat'.显然,OpenCV没有正确地链接到我的项目.

因此,我在网上搜索并尝试了一种可能的解决方案,就是这样

CONFIG += link_pkgconfig
PKGCONFIG += opencv

令我惊讶的是,它工作,并没有再次链接错误.

但是,我仍然无法理解为什么它不能以第一种方式工作,因为我已经在Mac OS X上以这种方式成功设置了我的项目.为什么它现在不适用于我的Ubuntu？

我试过pkg-config --libs opencv,结果是

-L/usr/local/lib -lopencv_calib3d -lopencv_contrib -lopencv_core -lopencv_features2d -lopencv_flann -lopencv_gpu -lopencv_highgui -lopencv_imgproc -lopencv_legacy -lopencv_ml -lopencv_nonfree -lopencv_objdetect -lopencv_ocl -lopencv_photo -lopencv_stitching -lopencv_superres -lopencv_ts -lopencv_video -lopencv_videostab -ltbb -lXext -lX11 -lICE …