cmake - How do you set CMAKE_C_COMPILER and CMAKE_CXX_COMPILER for building Assimp for iOS?

Question

When I try to build Assimp by running build_ios.sh, it tells me:

CMake Error: your C compiler: "/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/llvm-gcc" was not found.   Please set CMAKE_C_COMPILER to a valid compiler path or name.
CMake Error: your CXX compiler: "/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/llvm-g++" was not found.   Please set CMAKE_CXX_COMPILER to a valid compiler path or name.

What I need the path to be is:

/Applications/XCode.app/Contents/Developer/Platforms/...

I've tried changing DEVROOT in build_ios.sh and IPHONE_xxxx_TOOLCHAIN.cmake, because that's what CMAKE_C_COMPILER etc seem to get generated from, but it still gives me the same errors.

Answer 1

Option 1:

You can set CMake variables at command line like this:

cmake -D CMAKE_C_COMPILER="/path/to/your/c/compiler/executable" -D CMAKE_CXX_COMPILER "/path/to/your/cpp/compiler/executable" /path/to/directory/containing/CMakeLists.txt

See this to learn how to create a CMake cache entry.

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Option 2:

In your shell script build_ios.sh you can set environment variables CC and CXX to point to your C and C++ compiler executable respectively, example:

export CC=/path/to/your/c/compiler/executable
export CXX=/path/to/your/cpp/compiler/executable
cmake /path/to/directory/containing/CMakeLists.txt

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Option 3:

Edit the CMakeLists.txt file of "Assimp": Add these lines at the top (must be added before you use project() or enable_language() command)

set(CMAKE_C_COMPILER "/path/to/your/c/compiler/executable")
set(CMAKE_CXX_COMPILER "/path/to/your/cpp/compiler/executable")

See this to learn how to use set command in CMake. Also this is a useful resource for understanding use of some of the common CMake variables.

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Here is the relevant entry from the official FAQ: https://gitlab.kitware.com/cmake/community/wikis/FAQ#how-do-i-use-a-different-compiler