I am building something from source. My system's gcc and stdlibc++ are too old, but there is a clang build I can use. By default, clang uses stdlibc++, but libc++ may optionally be installed for clang to use.
What is the best way to check if libc++ is installed with clang?
Slightly better answer than @n.n:
printf "#include <ciso646>\nint main () {}" | clang -E -stdlib=libc++ -x c++ -dM - | grep _LIBCPP_VERSION
If that prints something like: #define _LIBCPP_VERSION 3700, then you've got libc++.
#include<ciso646>, I refer you to stackoverflow.com/questions/31657499/… (which amusingly enough is in response to another answer I gave), and clang++ -E -dM tells clang not to compile the source, but just to preprocess it (the -E) and then to print out all the things that are defined (the -dM)The most straightforward way to check if libc++ is installed is to use it on a trivial program:
clang++ -xc++ -stdlib=libc++ - <<EOF
int main(){}
EOF
If this fails, you don't have libc++.
In a real-world application, add user-supplied compiler and linker options:
clang++ $(CXXFLAGS) $(LDFLAGS) -xc++ -stdlib=libc++ - <<EOF
so that the user has a chance to specify that libc++ is installed in a non-standard place.
Here's how to check if a library is installed:
Type ldconfig -p | grep libc++ into the terminal. It does not matter what system you are using. If libc++ is not installed, the terminal will not say anything. If it is installed, it will display the available versions.
It's possible you get a confusion that both gcc and clang do. To compile code as C++, you have to use g++ instead of gcc, respectively clang++ instead of clang.
I doubt the libc++ libraries themselves are missing, since it's almost certain some program depends on them.
clang++explicitly as command.