#include <iostream>
using namespace std;
int main(){
std::cout << "Hello World\n";
return 0;
}
command 1 (works)
clang hello.cc -o hello -lc++
command 2 (don't works)
/path/to/custom/clang hello.cc -o hello -lc++
main.cc:2:10: fatal error: 'iostream' file not found
#include <iostream>
^
1 error generated.
Why I can't compile with command 2 ?
It looks like you're trying to compile C++ with a C compiler. Try running clang++ instead.
clang++ hello.cc -o hello
Without running clang as a C++ compiler it won't have the C++ standard library headers available for you to include. Using clang++ the C++ standard library headers are available and the C++ standard library is linked for you automatically.
That is a known Ubuntu issue. Their clang just isn't set up right. I complained about it here -- and this remained unfixed for years.
But the good news is that it now works with the most recent 16.10 release.
Edit: Based on your updated question I would say that "custom clang" does not know about its include files.
Related
I am having trouble installing a dependency for a program that itself depends on pcre.h. I have this installed to /opt/local/include, but the C compiler does not see it and thus gives me:
error: pcre.h: No such file or directory
I have confirmed this by writing a hello world program that tries to include it:
#include <pcre.h>
#include <stdio.h>
int main(void)
{
printf("hello, world\n");
return 0;
}
This also gives the error unless I specify the path as </opt/local/include/pcre.h>.
I would like the C compiler to find this by default but I do not know where this is configured. Tab completion hasn't revealed any HEADER_PATH environment variables and I cannot find anything like it that isn't specific to XCode. I am, however, using Mac OSX Snow Leopard on the off chance that makes a difference.
Use -I /opt/local/include on the command line or C_INCLUDE_PATH=/opt/local/include in the environment.
Use the pcre-config utility to get the right flags:
$ pcre-config --libs --cflags
-L/opt/local/lib -lpcre
-I/opt/local/include
If you're compiling via the command line,
$ gcc -Wall -g `pcre-config --libs --cflags` main.c
I would like to experiment with newer C++ features from (at least) C++20 and I'm new to C++ development on macOS in particular.
How do I enable importing of library headers in the 'module way'?
import <iostream>;
using namespace std;
int main(int argc, const char * argv[]) {
cout << "Hello, World!\n";
return 0;
}
The build errors are
Use of undeclared identifier 'iostream'
Use of undeclared identifier 'std'
I was looking at this answer and tried installing llvm and I suppose that I could run the provided commands from the terminal, but I have not tried. Is there a way to make Xcode issue the commands provided in that answer (see below)? Where would I enter them in XCode? And what do they do? I'd like to avoid thinking about terminal commands and just have something that works.
/opt/homebrew/opt/llvm/bin/clang++ -std=c++20 -c -Xclang -emit-module-interface mathlib.cpp -o mathlib.pcm
/opt/homebrew/opt/llvm/bin/clang++ -std=c++20 -fmodules -c -fprebuilt-module-path=. main.cpp -o main.o
/opt/homebrew/opt/llvm/bin/clang++ -std=c++2a -fmodules -o main main.o *.pcm
I saw that when making a new C++ project, Xcode defaults to the Apple Clang compiler and GNU++20 [-std=gnu++20] C++ Language dialect. There is also another option C++20 [-std=c++20] (what's the difference?) which I also tried, resulting in the same errors.
FYI, when I do clang -v I get
Apple clang version 14.0.0 (clang-1400.0.29.102)
Target: arm64-apple-darwin21.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
And a general question about other build systems such as CMake, which I discovered during my research for C++ compilation on mac. After making a CMake project, is it possible to use the regular IDE tools such as code suggestions and debugging?
I'm aware that C++20 is not fully supported (yet) by the compilers, but I really want to learn modules and other C++20 stuff.
Modules are supported in GCC11 and Clang-8+.
Compiler Support of C++20
I've installed Clang-10 on my Ubuntu, but it still gives me errors:
import <iostream>;
using namespace std;
int main(){
cout << "Hello world";
}
What am I doing wrong?
COMMANDS:
clang++ -Wall -std=c++2a -stdlib=libc++ -fimplicit-modules
-fimplicit-module-maps main.cpp -o main
clang++ -Wall -std=c++20 -stdlib=libc++ -fimplicit-modules
-fimplicit-module-maps main.cpp -o main
ERROR: fatal error: 'iostream' file not found
Although c++20 adds modules the c++20 standard library doesn't expose any modules.
Microsoft have implemented some standard library modules which may or may not match a future c++ standard: https://learn.microsoft.com/en-us/cpp/cpp/modules-cpp?view=msvc-160#consume-the-c-standard-library-as-modules. With these your example would be:
import std.core;
using namespace std;
int main(){
cout << "Hello world";
}
As far as I can see neither libc++ or libstdc++ have implemented any modules yet.
By default, gcc trunk use c++17, and clang trunk use c++14, so you have to say compiler, that you want to use c++20
If you are compiling your code in terminal by yourself, than add following flag
--std=c++2a
If you compile your code using Cmake, than add following to your CMakeLists.txt
set(CMAKE_CXX_STANDARD 20)
And if you compile in some IDE(Codeblocks or Visual studio), than somewhere in compiler settings put supporting c++20
trunk means "the main line of development", so this compiler version should be latest officially supported
I am trying to use the boost library with QT on windows. I've successfully build the library and also managed to include it in my project. However, on including gmp (#include "boost/multiprecision/gmp.hpp") and creating an object (boost::multiprecision::mpz_int myint;) I get the following error:
C:\Users\Laurenz\Documents\libraries\boost_1_66_0\include\boost\multiprecision\gmp.hpp:31: error: gmp.h: No such file or directory
And indeed, I haven't been able to find any such file in the boost directory. What did I do wrong?
Install the dependency and link to it. (See What is an undefined reference/unresolved external symbol error and how do I fix it?)
Alternatively, consider not using GMP, using cpp_int.hpp instead.
Since you already installed the GMP library, here's the last step:
Live On Coliru
#include <boost/multiprecision/gmp.hpp>
#include <iostream>
int main() {
boost::multiprecision::mpz_int i("1238192389824723487823749827349879872342834792374897923479");
std::cout << pow(i, 3) << "\n";
}
Note the -lgmp flag at the end of the compile/link command:
g++ -std=c++11 -O2 -Wall -Wextra -pedantic main.cpp -o demo -lgmp
Running it:
./demo
1898298004808110659499396020993351679788129852647955073547637871096272981567489303363372689896302906549189545322451852317205769760555889831589125591739044248515246136031239
My code:
#include <iostream>
#include <string>
int main()
{
std::string test = "45";
int myint = std::stoi(test);
std::cout << myint << '\n';
}
Gives me the compile error:
error: 'stoi' is not a member of 'std'
int myint = std::stoi(test);
^
However, according to here, this code should compile fine. I am using the line set(CMAKE_CXX_FLAGS "-std=c++11 -O3") in my CMakeLists.txt file.
Why is it not compiling?
Update: I am using gcc, and running gcc --version prints out:
gcc (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010
In libstdc++, the definitions of stoi, stol, etc., as well as the to_string functions, are guarded by the condition
#if ((__cplusplus >= 201103L) && defined(_GLIBCXX_USE_C99) \
&& !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))
I have had this fail on one platform before (namely Termux on Android), resulting in to_string not being available even with g++ 6.1 and the C++14 standard. In that case, I just did
#define _GLIBCXX_USE_C99 1
before including anything, and voilà, suddenly the functions existed. (You should put this first, or even on the command line, rather than just before including <string>, because another header may include <string> first, and then its include guards will keep it from ever seeing your macro.)
I did not investigate why this macro wasn't set in the first place. Obviously this is a cause for concern if you want your code to actually work (in my case I didn't particularly, but FWIW there were no problems.)
You should check if _GLIBCXX_USE_C99 is not defined, or if _GLIBCXX_HAVE_BROKEN_VSWPRINTF is defined (which may be the case on MinGW?)
std::stoi is a C++11 function. You have to use the -std=c++11 to enable it in both g++ and clang++. This is the actual issue, not a linking error or a specific preprocessor define.
$ cat test.cxx
#include <iostream>
#include <string>
int main()
{
std::string test = "45";
int myint = std::stoi(test);
std::cout << myint << '\n';
}
$ g++ -otest test.cxx
test.cxx: In Funktion »int main()«:
test.cxx:7:17: Fehler: »stoi« ist kein Element von »std«
int myint = std::stoi(test);
^
$ g++ -otest test.cxx -std=c++11
$ ./test
45
$
edit: I just saw that you used c++11. Are you sure that's making it into your compile options? Check the generated makefile and watch the executed commands to be certain.
Your version seems up to date, so there shouldn't be an issue. I think it may be related to gcc. Try g++ instead.(Most likely automatically linking issue. If you just run gcc on a C++ file, it will not 'just work' like g++ does. That's because it won't automatically link to the C++ std library, etc.). My second advise is try std::atoi.
# I have fixed the issue. std::stoi uses libstdc++. It is about The GNU Standard C++ Library. In gcc you have to link adding -lstdc++. However, in g++, libstdc++ is linked automatically.
using gcc and using g++
Pay attention how it is compiled
using g++: g++ -std=c++11 -O3 -Wall -pedantic main.cpp && ./a.out
using gcc: gcc -std=c++11 -O3 -Wall -pedantic -lstdc++ main.cpp && ./a.out
I think you should set flag like set(CMAKE_EXE_LINKER_FLAGS "-libgcc -lstdc++") (Not tested)
#include <cstdlib>
int myInt = std::atoi(test.c_str());
If you are using Cmake to compile, add line:
"add_definitions(-std=c++11)"
after find_package command.
Use 'set(CMAKE_CXX_STANDARD 11)' for Cmake