1

环境介绍：windows10, visual studio2019, CMake, OPENCV4.5.5

出现问题

IPPICV: Download: ippicv_2020_win_intel64_20191018_general.zip
Try 1 failed
CMake Warning at cmake/OpenCVDownload.cmake:202 (message):
  IPPICV: Download failed: 3;"URL using bad/illegal format or missing URL"

  For details please refer to the download log file:

  D:/OPENCV455/build/CMakeDownloadLog.txt

Call Stack (most recent call first):
  3rdparty/ippicv/ippicv.cmake:37 (ocv_download)
  cmake/OpenCVFindIPP.cmake:259 (download_ippicv)
  cmake/OpenCVFindLibsPerf.cmake:12 (include)
  CMakeLists.txt:732 (include)

2 解决方法

1 链接失效，需要手动下载文件

https://github.com/opencv/opencv_3rdparty/tree/ippicv/master_20191018/ippicv

下载文件ippicv_2020_win_intel64_20191018_general.zip

得挂梯子可能

2 修改链接IPPICV下的cmake文件

路径

D:\OPENCV455\sources\opencv-4.5.5\3rdparty\ippicv

将其中的链接地址修改

  ocv_download(FILENAME ${OPENCV_ICV_NAME}
               HASH ${OPENCV_ICV_HASH}
               URL
                 "file:/D:/OPENCV455"
               DESTINATION_DIR "${THE_ROOT}"
               ID IPPICV
               STATUS res
               UNPACK RELATIVE_URL)

重新使用cmake gui进行configure发现依旧报错

根据指示打开build文件夹中的CMakeDownloadLog.txt文件

#use_cache "D:/OPENCV455/sources/opencv-4.5.5/.cache"
#do_unpack "ippicv_2020_win_intel64_20191018_general.zip" "879741a7946b814455eee6c6ffde2984" "file:D:/OPENCV455/ippicv_2020_win_intel64_20191018_general.zip" "D:/OPENCV455/build/3rdparty/ippicv"
#cmake_download "D:/OPENCV455/sources/opencv-4.5.5/.cache/ippicv/879741a7946b814455eee6c6ffde2984-ippicv_2020_win_intel64_20191018_general.zip" "file:D:/OPENCV455/ippicv_2020_win_intel64_20191018_general.zip"
#try 1
# Closing connection -1
# 

貌似是由于MD5不匹配导致，大致是因为哈希表无法对应？我不理解更深层次的原因。
也有可能是我写的windows下的本地路径格式有问题。

3 按照指示复制修改文件名称

将原先下载的ippicv_2020_win_intel64_20191018_general.zip复制到D:\OPENCV455\sources\opencv-4.5.5\.cache\ippicv路径下，并根据重命名为879741a7946b814455eee6c6ffde2984-ippicv_2020_win_intel64_20191018_general.zip

成功解决