Clang doesn't see basic headers - c++

Question

I've tried to compile simple hello world on Fedora 20 with Clang, and I get the following output:
d.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
I don't have any idea how to resolve it.

Answer 1

This is because g++ is not installed, so libstdc++ is not present.
You can install g++, or if LLVM is preferred, install LLVM libc++ and specify that you want to use it, like so:
sudo apt-get install libc++-dev
clang++ -stdlib=libc++ <rest of arguments>
You may wish to link /usr/bin/c++ to the default compiler:
ln -s /usr/bin/c++ /usr/bin/clang++-libc++
and then compile simply using
$ c++ <args_as_usual>

Answer 2

Point 3 solved the problem for me.
1.
Had the same issue, fedora 21::clang 3.5.0:
clang++ -std=c++14 -pedantic -Wall test_01.cpp -o test_01 -v
2.
ignoring nonexistent directory "/usr/lib/gcc/i686-redhat-linux/4.9.2/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/usr/bin/../lib/clang/3.5.0/include
/usr/include
End of search list.
test_01.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
3.
sudo yum install gcc-c++
4.
#include "..." search starts here:
#include <...> search starts here:
/bin/../lib/gcc/i686-redhat-linux/4.9.2/../../../../include/c++/4.9.2
/bin/../lib/gcc/i686-redhat-linux/4.9.2/../../../../include/c++/4.9.2/i686-redhat-linux
/bin/../lib/gcc/i686-redhat-linux/4.9.2/../../../../include/c++/4.9.2/backward
/usr/local/include
/usr/bin/../lib/clang/3.5.0/include
/usr/include
/usr/lib/gcc/i686-redhat-linux/4.9.2/include
End of search list.

Answer 3

One of the reason could be this:
clang doesn't have its own header libraries for c++, so it is pointing towards gcc's library folder to access header files. You can check it out and confirm it by using command
clang -v
This will print its version and the selected gcc installation which will help you to know which version of gcc it is using. For me it was,
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;#m64
Selected multilib: .;#m64
Now as it can be seen that it has selected gcc's 12th version which I didn't had installed and thus the error because it can't find one(don't know how it selected that version even though I haven't installed it). But the solution is to install g++ nth version. You can do that by following command where n is the version number that's selected by gcc and you're good to go.
sudo apt install g++-n
I got this answer after digging alot and found this blog clangmissingheaders

Answer 4

Looks like you should provide your clang build with -stdlib option. One of -stdlib=libc++ or -stdlib=libstdc++ will probably work.
There are more details on your subject:
When is it necessary to use the flag -stdlib=libstdc++?

Answer 5

-stdlib=libstdc++ solved it for me. Here is my complete tasks.json config:
{
"tasks": [
{
"type": "shell",
"label": "clang++ build active file",
"command": "clang++",
"args": [
"-std=c++11",
"-stdlib=libstdc++",
"hello.cpp",
"-o",
"hello.out",
"--debug"
],
"group": {
"kind": "build",
"isDefault": true
}
}
],
"version": "2.0.0"

Answer 6

I had a similar issue after updating using Pop!_OS 22.04 LTS x86_64.
OUTLINE OF ISSUE:
Compilation worked just fine so gcc and g++ was working perfectly but the lsp clangd was just throwing ERROR in my editor (neovim) for lines containing anything involving iostream.
Here was my path to refuge:
Created a env (environment) variable that clangd looks for called CLANGD_FLAGS and assigned it the path to my c++ 11 path and putting this into my .bashrc file like so:
code added to my .bashrc:
export CLANGD_FLAGS="-I/usr/include/c++/11"
NOTE:
your path may vary obviously.. Just be sure to precede your path with the -I option.
you can also just link the path to a compile_commands.json file if you desire more settings or specifics
ex:
export CLANGD_FLAGS="--compile-commands-dir=/path/to/compile_commands.json --flag1 --flag2"
This allowed me to access <iostream> globally and avoid writing the compile_commands.json for each new program or project.

Answer 7

For anyone Googling this & have a MacOS, here's the solution I found:
Add the following to your .bashrc/.zshrc file
export CPLUS_INCLUDE_PATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1
This should fix it.

Answer 8

Make sure you have the libstdc++ installed that corresponds to the latest verison of gcc installed. Clang seems to identify the latest gcc installation and only look in the appropriate directories for that version.

Answer 9

I've tried to reinstall command line tools and the "ln" command, but it still cannot be fixed.
And after trying almost every other solution on the website, this still cannot be fixed. But the thing is going to be clear: the compiler attempted to find the header files in /usr/include, but although with installed command line tools, there is no this folder at all.
Maybe the best straightforward approach for us is installing the Xcode and coding in this IDE, or other compilers, but not the most lower-cost situation.
Mac has a built-in Clang, we do not need to install extra compilers. Here are the steps.
We can check the CommandLineToos folder, if you haven't installed it, try this command to install it in advance.
xcode-select --install
In the CommandLineTools folder, we may check the route of SDKs, which is /Library/Developer/CommandLineTools/SDKs
/Library/Developer/CommandLineTools/SDKs
We may use MacOSX.sdk, for me, it is also MacOSX12.0.sdk, to find the headers. The C basic headers is found at /Library/Developer/CommandLineTools/SDKs/MacOSX12.0.sdk/usr/include.
/Library/Developer/CommandLineTools/SDKs/MacOSX12.0.sdk/usr/include
But it doesn't contained with C++ basic headers, the C++ basic headers can be found at /Library/Developer/CommandLineTools/usr/include. We can find this route with command g++ -v in the terminal as well.
g++ -v
So the solution will be obvious, type the follow commands in terminal.
Open the bash_profile.
open ~/.bash_profile
Add this.
export C_INCLUDE_PATH=/Library/Developer/CommandLineTools/SDKs/MacOSX12.0.sdk/usr/include
export CPLUS_INCLUDE_PATH=/Library/Developer/CommandLineTools/usr/include
Source it.
source ~/.bash_profile
This error will be fixed.

Answer 10

In my case, clang was using version 12 of GCC installation, but I was missing the libstdc++ for that version:
$ clang -v
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Fixed it like this:
sudo apt install libstdc++-12-dev

Answer 11

TL;DR: If you don't have sudo access and are using conda, you might want to do:
conda install gxx -c conda-forge
In my case I installed clang++ using conda install clangxx thinking it would install the required dependencies but turns out I was missing libstdgxx-devel. I guess it's one of the dependencies of gxx so it gets installed as a side effect.