在编译OpenCV以及其附加模块时，有时会需要一些第三方的库，如果本地没有，会自动下载，下载地址一般为GitHub，结果当然就是卡死在那里，根本无法下载，下面教大家如何解决这种问题。

问题重现

比如我在使用cmake配置的过程中出现以下情况：

Call Stack (most recent call first):

/home/ryan/build/opencv_contrib-master/modules/dnn/cmake/download_protobuf.cmake:23 (ocv_download)

/home/ryan/build/opencv_contrib-master/modules/dnn/cmake/download_protobuf.cmake:51 (ocv_protobuf_download)

/home/ryan/build/opencv_contrib-master/modules/dnn/cmake/OpenCVFindLibProtobuf.cmake:30 (include)

/home/ryan/build/opencv_contrib-master/modules/dnn/CMakeLists.txt:38 (include)

-- Downloading v3.1.0/protobuf-cpp-3.1.0.tar.gz...

解决思路

从上面的日志中可以得到以下信息：

需要下载protobuf-cpp-3.1.0.tar.gz这个文件

最先报错的是download_protobuf.cmake这个文件

一般情况下，最先报错的那个文件能获得一些与错误相关的信息，于是，我们打开这个文件，如下

set(PROTOBUF_CPP_NAME "libprotobuf")

set(PROTOBUF_CPP_DOWNLOAD_HASH "bd5e3eed635a8d32e2b99658633815ef")

set(PROTOBUF_CPP_PATH "${CMAKE_CURRENT_BINARY_DIR}/3rdparty/protobuf/sources") # /protobuf-3.1.0 subdirectory

set(OPENCV_PROTOBUF_CPP_DOWNLOAD_URL ${OPENCV_PROTOBUF_URL};$ENV{OPENCV_PROTOBUF_URL};https://github.com/google/protobuf/releases/download/)

function(ocv_protobuf_download file ID)

if(DEFINED ${ID}_DOWNLOADED_HASH

AND ${ID}_DOWNLOADED_HASH STREQUAL ${ID}_DOWNLOAD_HASH

AND EXISTS ${${ID}_PATH})

# Files have been downloaded and checked by the previous CMake run

return()

else()

if(EXISTS ${${ID}_PATH})

message(STATUS "${${ID}_NAME}: Removing previous unpacked files: ${${ID}_PATH}")

file(REMOVE_RECURSE ${${ID}_PATH})

endif()

endif()

unset(${ID}_DOWNLOADED_HASH CACHE)

file(MAKE_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/.download)

file(WRITE "${CMAKE_CURRENT_SOURCE_DIR}/.download/.gitignore" "*\n")

ocv_download(PACKAGE ${file}

HASH ${${ID}_DOWNLOAD_HASH}

URL ${OPENCV_${ID}_DOWNLOAD_URL}

DOWNLOAD_DIR ${CMAKE_CURRENT_SOURCE_DIR}/.download)

set(${ID}_ARCHIVE "${DOWNLOAD_PACKAGE_LOCATION}")

ocv_assert(EXISTS "${${ID}_ARCHIVE}")

ocv_assert(NOT EXISTS "${${ID}_PATH}")

file(MAKE_DIRECTORY ${${ID}_PATH})

ocv_assert(EXISTS "${${ID}_PATH}")

file(WRITE "${${ID}_PATH}/.gitignore" "*\n")

message(STATUS "${${ID}_NAME}: Unpacking ${file} to ${${ID}_PATH}...")

execute_process(COMMAND ${CMAKE_COMMAND} -E tar xz "${${ID}_ARCHIVE}"

WORKING_DIRECTORY "${${ID}_PATH}"

RESULT_VARIABLE __result)

if(NOT __result EQUAL 0)

message(FATAL_ERROR "${${ID}_NAME}: Failed to unpack ${ID} archive from ${${ID}_ARCHIVE} to ${${ID}_PATH} with error ${__result}")

endif()

ocv_assert(EXISTS "${${ID}_PATH}")

set(${ID}_DOWNLOADED_HASH "${${ID}_DOWNLOAD_HASH}" CACHE INTERNAL "${ID} hash")

#message(STATUS "${${ID}_NAME}: Successfully downloaded")

endfunction()

ocv_protobuf_download(v3.1.0/protobuf-cpp-3.1.0.tar.gz PROTOBUF_CPP)

可以看出，他需要libprotobuf这个库，并且需要下载到 ${CMAKE_CURRENT_BINARY_DIR}/3rdparty/protobuf/sources 目录下，而下载地址就是 https://github.com/google/protobuf/releases/download/ ，于是我们只要手动下载，然后把文件放到这个目录下即可。

Ubuntu 16.04下Matlab2014a+Anaconda2+OpenCV3.1+Caffe安装  http://www.linuxidc.com/Linux/2016-07/132860.htm

Ubuntu 16.04下TensorFlow+Caffe+OpenCV3.1+Theano部署  http://www.linuxidc.com/Linux/2017-01/139503.htm

OpenCV的详细介绍：请点这里

OpenCV的下载地址：请点这里