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I have installed Clang by using apt-get in Ubuntu, and I can successfully compile C files using it. However, I have no idea how to compile C++ through it. What do I need to do to compile C++?

Peter Mortensen
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pythonic
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6 Answers6

198

The command clang is for C, and the command clang++ is for C++.

adl
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103

I do not know why there is no answer directly addressing the problem. When you want to compile C++ program, it is best to use clang++, instead of using clang. For example, the following works for me:

clang++ -Wall -std=c++11 test.cc -o test

If compiled correctly, it will produce the executable file test, and you can run the file by using ./test.

Or you can just use clang++ test.cc to compile the program. It will produce a default executable file named a.out. Use ./a.out to run the file.

The whole process is a lot like g++ if you are familiar with g++. See this post to check which warnings are included with -Wall option. This page shows a list of diagnostic flags supported by Clang.

A note on using clang -x c++: Kim Gräsman says that you can also use clang -x c++ to compile CPP programs, but that may not be always viable. For example, I am having a simple program below:

#include <iostream>
#include <vector>

int main() {
    /* std::vector<int> v = {1, 2, 3, 4, 5}; */
    std::vector<int> v(10, 5);
    int sum = 0;
    for (int i = 0; i < v.size(); i++){
        sum += v[i]*2;
    }
    std::cout << "sum is " << sum << std::endl;
    return 0;
}

clang++ test.cc -o test will compile successfully, but clang -x c++ will not, showing a lot of undefined reference errors. So I guess they are not exactly equivalent. It is best to use clang++ instead of clang -x c++ when compiling c++ programs to avoid extra troubles.

  • clang version: 11.0.0
  • Platform: Ubuntu 16.04
jdhao
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    Thanks for actually answering the question. – Curyous Sep 08 '18 at 08:03
  • @jdhao Thanks for the detailed answer. But there is one thing I do not understand. You said "When you want to compile C++ program, it is best to use clang++". Why using `g++` is not recommended? – Mr.Robot Jan 28 '21 at 16:48
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    @Mr.Robot I mean it is best to use `clang++` for compiling cpp, compared to using `clang`, not compared to using `g++`. – jdhao Jan 29 '21 at 01:53
  • What about on Windows? – Andrew Feb 14 '21 at 03:29
  • @Andrew I do not use clang on Windows. So I am not sure. If you use clang on Windows, it is easy to verify. – jdhao Feb 15 '21 at 03:44
57

Also, for posterity -- Clang (like GCC) accepts the -x switch to set the language of the input files, for example,

$ clang -x c++ some_random_file.txt

This mailing list thread explains the difference between clang and clang++ well: Difference between clang and clang++

Peter Mortensen
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Kim Gräsman
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    I had an linker error with _clang -x c++_ when compiled cpp file with `#include `. _-lstdc++_ flag solved this problem. – Slav Oct 02 '15 at 16:17
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    I have the source code of Clang in front of my eyes now. During build (on Windows), it first builds `clang.exe`, and then copies that executable into `clang++.exe`. So it's the same executable, just at runtime it checks its own name to distinguish whether to behave as C or C++ compiler. HTH. – Serge Rogatch Jan 06 '17 at 12:05
  • As a note, the option `-x c++` was very useful to give as an `-extra-arg` to *clang-tidy*, to force it to treat a .h file as containing C++ instead of C. – Ad N Nov 17 '17 at 15:58
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    This is too limiting to be actually useful unless you build entire thing from source. It's better to just use `clang++` and let it detect what kind of files you supply to it. When a project can contain `.cpp` files, `.ll` files (llvm ir) and `.o`, `.a`, `.so` and what not files from third party libraries, `clang -x c++` will just throw up. –  Dec 07 '19 at 11:53
  • I am also seeing the same issue as @Slav. For a very simple program, `clang++` works, but `clang -x c++` shows a lot of undefined reference errors (the other flags are the same). So I guess it is best to use `clang++`. Tested clang version: 11.0.0. – jdhao Nov 11 '20 at 02:05
6

Solution 1:

  clang++ your.cpp

Solution 2:

  clang your.cpp -lstdc++

Solution 3:

   clang -x c++ your.cpp
Peter Mortensen
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ligand
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5

I've had a similar problem when building Clang from source (but not with sudo apt-get install. This might depend on the version of Ubuntu which you're running).

It might be worth checking if clang++ can find the correct locations of your C++ libraries:

Compare the results of g++ -v <filename.cpp> and clang++ -v <filename.cpp>, under "#include < ... > search starts here:".

Peter Mortensen
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Guy Adini
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4

Open a Terminal window and navigate to your project directory. Run these sets of commands, depending on which compiler you have installed:

To compile multiple C++ files using clang++:

$ clang++ *.cpp 
$ ./a.out

To compile multiple C++ files using g++:

$ g++ -c *.cpp 
$ g++ -o temp.exe *.o
$ ./temp.exe
blastoise
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