I am curious about the C++ Modules TS. I have played a little around with Clang's implementation. Only one or two files or so at a time.
Now I would like to try something bigger than that. And I would like to use CMake.
Does someone know if there is some good way to use the Clang modules implementation with CMake or are there already some CMake modules which help me with this?
I would really like to know. Otherwise I have to consider using a different build system.
I would suggest you try build2:
https://build2.org/build2/doc/build2-build-system-manual.xhtml#cxx-modules
It supports modules for Visual Studio, gcc and clang. And for gcc there is a package that contains the standard library:
https://build2.org/pkg/hello/libstd-modules?f=full&q=library
Note that Microsoft implementation, as of Visual Studio 2017 update 4, is using the old syntax in the .ixx files (module xyz; instead of export module xyz; where the latter is what the last Modules TS draft mandates)
It shouldn't be any harder than configuring the proper command-line arguments. Since this feature has yet to be standardized and is different between the two known implementations (clang and MSVC -- gcc 7.2 documentation doesn't mention modules that I could find), I don't expect there are any CMake functions to handle anything.
AFAIK, the clang way of treating headers as special if they are in the module map file is lagging the current working draft for modules. IMO, it would be more useful to experiment with MSVC which is more closely tracking the WD for modules at this time. I don't know why g++ and clang are lagging here, they are usually early adopters. Perhaps it is because the specification is still in working draft stage and not yet a TS, I don't know.
Related
I needed to work with postgreSQL and C++ so the most common library out there for this is libpqxx. I cloned the repo and switched to latest branch available right now (branch 7.6) and then used CMake to build the visual studio solution file.
But I cannot build this with latest preview features language standard OR even C++20 language standard. After searching for a bit I discovered that the error related to the header file ciso646 has something to do with C++20 removing != operator. This is very annoying as now I cannot make my project's language standard as C++20 either because of this. Here is a screenshot of the build errors:
So I reduced the language standard to C++17 and then tried to build and it still gave me a LOT of warnings before getting built successfully. The warnings were something of the sort:
warning C5051: attribute 'likely' requires at least '/std:c++20'; ignored
Even though now it is built and I got my include and lib files I am not sure if these warnings can cause any problems for me in the future.
Anyhow my question is can something be done to be able to build this library using c++20 or am I stuck working with c++17 because of this?
I downloaded Clang 3.6.2 from this website and am trying to set it up with Code::Blocks under Windows. Unfortunately, it fails to compile a simple "hello world" program on the grounds that it doesn't know where iostream is.
Looking through the install folder, it does not appear to include a standard library with it. Why? And how do I get it?
The standard library is NOT part of the compiler itself. It is part of the runtime environment on a particular platform. Sure, some organisations put together a "kit" with all the necessary parts to build an application - there may even be someone that packages a Clang compiler with a suitable runtime.
In general, you should be able to download the Windows SDK and get the relevant header files there - and if you use clang-cl, it should be largely compatible with the MSVC compiler [or provide clang or clang++ with the correct -fms-compatibility or whatever it is called].
Or as suggested in the other answer, use libcxx, but it's not 100% complete for Windows.
They do have a c++ standard library: libcxx.llvm.org. But it's not fully supported on the windows platform.
I have searched Google but haven't found quite a direct answer to my queries.
I have been reading C++ Primer and I'm still quite new to the language, but despite how good the book is it discusses the use of the standard library but doesn't really describe where it is or where it comes from (it hasn't yet anyway). So, where is the standard library? Where are the header files that let me access it? When I downloaded CodeBlocks, did the STL come with it? Or does it automatically come with my OS?
Somewhat related, but what exactly is MinGW that came with Cobeblocks? Here it says
MinGW is a C/C++ compiler suite which allows you to create Windows executables without dependency on such DLLs
So at the most basic level is it just a collection of "things" needed to let me make C++ programs?
Apologies for the quite basic question.
"When I downloaded CodeBlocks, did the STL come with it?"
Despite it's not called the STL, but the C++ standard library, it comes with your c++ compiler implementation (and optionally packaged with the CodeBlocks IDE).
You have to differentiate IDE and compiler toolchain. CodeBlocks (the Integrated Development Environment) can be configured to use a number of different compiler toolchains (e.g. Clang or MSVC).
"Or does it automatically come with my OS?"
No, usually not. Especially not for Windows OS
"So, where is the standard library? Where are the header files that let me access it?"
They come with the compiler toolchain you're currently using for your CodeBlocks project.
Supposed this is the MinGW GCC toolchain and it's installed in the default directory, you'll find the libraries under a directory like (that's what I have)
C:\MinGW\lib\gcc\mingw32\4.8.1
and the header files at
C:\MinGW\lib\gcc\mingw32\4.8.1\include\c++
"So at the most basic level is it just a collection of "things" needed to let me make C++ programs?"
It's the Minimalist GNU toolchain for Windows. It usually comes along with the GCC (GNU C/C++ compiler toolchain), plus the MSYS minimalist GNU tools environment (including GNU make, shell, etc.).
When you have installed a C++ implementation you'll have something which implements everything necessary to use C++ source files and turn them into something running. How that is done exactly depends on the specific C++ implementation. Most often, there is a compiler which processes individual source file and translates them into object files which are then combined by a linker to produce an actual running program. That is by no means required and, e.g., cling directly interprets C++ code without compiling.
All this is just to clarify that there is no one way how C++ is implemented although the majority of contemporary C++ implementations follow the approach of compiler/linker and provide libraries as a collection of files with declarations and library files providing implementations of these declarations.
Where the C++ standard library is located and where its declarations are to be found entirely depends on the C++ implementations. Oddly, all C++ implementations I have encountered so far except cling do use a compiler and all these compilers support a -E option (although it is spelled /E for MSVC++) which preprocesses a C++ file. The typically quite large output shows locations of included files pointing at the location of the declarations. That is, something like this executed on a command line yields a file with the information about the locations:
compiler -E input.cpp > input.ii
How the compiler compiler is actually named entirely depends on the C++ implementation and is something like g++, clang++, etc. The file input.cpp is supposed to contain a suitable include directive for one of the standard C++ library headers, e.g.
#include <iostream>
Searching in the output input.ii should reveal the location of this header. Of course, it is possible that the declarations are made available by the compiler without actually including a file but just making declarations visible. There used to be a compiler like this (TenDRA) but I'm not aware of any contemporary compiler doing this (with modules being considered for standardization these may come back in the future, though).
Where the actual library file with the objects implementing the various declarations is located is an entirely different question and locating these tends to be a bit more involved.
The C++ implementation is probably installed somehow when installing CodeBlocks. I think it is just one package. On systems with a package management system like dpkg on some Linuxes it would be quite reasonable to just have the IDE have a dependency on the compiler (e.g., gcc for CodeBlocks) and have the compiler have a dependency on the standard C++ library (libstdc++ for gcc) and have the package management system sort out how things are installed.
There are several implementations of the C++ standard library. Some of the more popular ones are libstdc++, which comes packaged with GCC, libc++, which can be used with Clang, or Visual Studio's implementation by Microsoft. They use a licensed version of Dinkumware's implementation. MinGW contains a port of GCC. CodeBlocks, an IDE, allows you to choose a setup which comes packaged with a version of MinGW, or one without. Either way, you can still set up the IDE to use a different compiler if you choose. Part of the standard library implementation will also be header files, not just binaries, because a lot of it is template code (which can only be implemented in header files.)
I recommend you read the documentation for the respective technologies because they contain a lot of information, more than a tutorial or book would:
libstdc++ faq
MinGW faq
MSDN
I've been looking into some of the features of the "newer" C++ standards (C++11 and C++14), and that got me thinking about something. I'm currently using the VC++2008 compiler for my projects (for various reasons), which means that the newest standard I have access to is C++03, plus TR1. TR1 has some nice things in it, but there are features in C++11 and C++14 that would be nice to have.
My question is this: Would there be any way that I could build some code using a newer compiler (say MSVC2012 or 2013) to build libraries or DLLs using the newer C++11 and C++14 functionality and then link that into my project that's running the '08 compiler?
The only thing that I could think of that wouldn't work would be anywhere I had to have a C++11 or C++14 feature in a header included by my '08 compiler project. However as long as everything "new" were hidden behind my interface, shouldn't this work?
Yes but its going to get ugly.. since the ABI is not compatible you'll have to go down to the "extern "C" {}" ABIness.
That means you can't pass C++ objects at all.. like I said, painful. It also means it must be a DLL since you won't be able to link in a static lib with another ABI.
Its up to you if its worth wrapping up a DLL in a C API just to use a couple of new features or not, I would recommend just upgraded the whole project though.
I almost forgot, you probably can't link the import lib either, so you'll have to have some code that uses LoadLibrary, GetProcAddress and FreeLibrary (did I mention this is ugly/painful?).
Unfortunately, what you're trying to do is not possible with MSVC. They intentionally break binary compatibility with every major release as stated in MSDN documentation:
To enable new optimizations and debugging checks, the Visual Studio implementation of the C++ Standard Library intentionally breaks binary compatibility from one version to the next. Therefore, when the C++ Standard Library is used, object files and static libraries that are compiled by using different versions can't be mixed in one binary (EXE or DLL), and C++ Standard Library objects can't be passed between binaries that are compiled by using different versions. Such mixing emits linker errors about _MSC_VER mismatches. (_MSC_VER is the macro that contains the compiler's major version—for example, 1800 for Visual C++ in Visual Studio 2013.) This check cannot detect DLL mixing, and cannot detect mixing that involves Visual C++ 2008 or earlier.
Your options are to then only pass around POD types, or implement COM interfaces to interop between the DLLs compiled using different version of the VC compiler, neither of which is particularly palatable.
My advice would be, if you must stick with VS2008 for certain legacy applications, suck it up and deal with the feature set it supports (at least you have TR1). For newer projects, try and talk your team into using newer versions of VC.
How do I check for presence of individual C++0x/C++11 language features? I know Clang has a nice system for this. What about GCC, Visual Studio or Boost? I guess one way to do it is to detect the compiler version and relate that to the features introduced in that version. But that is cumbersome. Has someone already done that?
boost config comes with a script to check for some but not all C++11 features.
It generates a config-file with macros for each feature.
Your build-tool may be able to help with this.
CMake has the try_compile command which allows you to test whether a code sample will compile and set a variable based on the result of compilation.
At the moment I've just been using the more commonly supported features such as auto typing.
You can often use Boost to replace the missing library features, and this may be the best option for a few year while compilers and libraries are updated and bugs fixed.
The C++11 feature compatibility list for GCC is here: http://gcc.gnu.org/projects/cxx0x.html
Note the warning:
Important: GCC's support for C++11 is still experimental. Some features were implemented based on early proposals, and no attempt will be made to maintain backward compatibility when they are updated to match the final C++11 standard.