ubuntu1804 編譯opencv2問題及解決辦法

opencv git倉庫地址：
https://github.com/opencv/opencv.git

git clone https://github.com/opencv/opencv.git
cd opencv/
git checkout tags/2.4.13
mkdir build
cd build/
#已將opencv3安裝到/usr/local，防止衝突，將opencv2安裝到/usr下
cmake \
-DCMAKE_BUILD_TYPE=RELEASE \
-DCMAKE_INSTALL_PREFIX=/usr \
\
-DWITH_CUDA=OFF \
\
-DBUILD_DOCS=OFF \
-DBUILD_EXAMPLES=OFF \
-DBUILD_TESTS=OFF \
-DBUILD_PERF_TESTS=OFF \
-D ENABLE_PRECOMPILED_HEADERS=OFF \
..

make -j4
sudo make install

cmake時，報錯：
Q1：linux/videodev.h not found
R1：
sudo ln -s /usr/include/libv4l1-videodev.h /usr/include/linux/videodev.h

Q2：sys/videoio.h not found
R2:

sudo cp /usr/include/opencv2/videoio/videoio_c.h  /usr/include/x86_64-linux-gnu/sys
sudo ln -s /usr/include/x86_64-linux-gnu/sys/videoio_c.h  /usr/include/x86_64-linux-gnu/sys/videoio.h

Q3：ffmpeg/avformat.h not found

R3：
sudo ln -s /usr/local/include/libavformat ffmpeg
參考:OpenCV-3編譯安裝方法及常見錯誤解決(Ubuntu平臺)

Q4: /usr/include/c++/7/cstdlib:75:15: fatal error: stdlib.h: 沒有那個檔案或目錄
R4：
cmake的時候後面加上：
-DENABLE_PRECOMPILED_HEADERS=OFF

make時報錯：
O5：/usr/bin/ld: /usr/local/lib/libavcodec.a(vc1dsp_mmx.o): relocation R_X86_64_PC32 against symbol `ff_pw’ can not be used when making a shared object; recompile with -fPIC
R5：
make -j CFLAGS=-fPIC