Here's what to do when CMAKE_C_COMPILER is set to a C++ compiler.
While compiling openCV, I ran into this error message:
"The CMAKE_C_COMPILER is set to a C++ compiler"
when I executed
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local ..
according to the openCV install guide
You need to tell cmake to use gcc as the compiler for c++ files, like so:
add this "-D CMAKE_C_COMPILER=gcc" to the cmake switches, for example:
cmake -D CMAKE_C_COMPILER=gcc -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local /tmp/opencv-3.0.0