I have the Microsoft Visual C++ Compiler Nov 2012 CTP (v120_CTP_Nov20..), but when I attempt to use variadic templates, I get this error:
error C3546: '...' : there are no parameter packs available to expand
Are they even supported yet? I've properly set to use the new toolchain from the project options and everything...
template<typename... T>
void Event<T...>::operator()(T... args)
{
for(uint i = 0; i < _listHandlers.Size(); i++)
{
(_listHandlers)[i](args...);
}
}
Did you pick it from Project Properties?
Check Variadic Template in VS 2012 (Visual C++ November 2012 CTP).
It works fine on my computer.
Related
I am getting the error
"'constexpr' is not valid here
and
E1449 explicit specialization of variable "tao::pegtl::internal::enable_control [with Rule=tao::pegtl::internal::bol]" must precede its first use () Pegtl \include\tao\pegtl\internal\bol.hpp 27
on the following line of code:
template<>
inline constexpr bool enable_control< bol > = false;
(on line 27 https://github.com/taocpp/PEGTL/blob/master/include/tao/pegtl/internal/bol.hpp)
the code compiles fine under VisualStudio 2019.
What difference between VisualStudio 2017 and 2019 could account for this error? and how can I get it compiling in VisualStudio 2017?
I am trying to compile the following piece of code in Visual Studio 2015 (Community version) but encountering the error shown further down below.
/*****Source Code Start*******/
constexpr char const* GetStatusAsCString(Status compute)
{
switch (compute)
{
case armnn::Status::Success: return "Status::Success";
case armnn::Status::Failure: return "Status::Failure";
default: return "Unknown";
}
}
/*****Source Code End*******/
Error message:
> Error (active) a constexpr function must contain exactly one return
> statement ArmNN_MnistTF_64b c:\armnn\armnn-devenv\armnn\include\armnn\TypesUtils.hpp 22
Note that i have made sure of the following settings:
Set the compiler front end as Clang in VS 2015:
I have set the C++ standard as C++14.
Can anyone please advise me on what else am I missing? Been struggling with this error for sometime now.
Visual Studio 2015 does not fully implement C++14 even as of VS 2015 Update 3 although it has a lot of it.
Specifically, N3652 Extended constexpr is not implemented until VS 2017. You should upgrade to the latest VS 2017 Community edition update (which at this point is 15.7)
See Visual C++ Language Conformance
I am using Visual Studio 2015 Update 3.
I get a fatal error:
(code C1001) : An internal error has occurred in the compiler.
Here is the code :
template<typename T>
constexpr T epsilon = std::numeric_limits<T>::epsilon();
I read it was fixed in Visual Studio Update 2. Can someone explain me why I am getting this error? Thanks in advance.
Any internal error (ICE) is a compiler bug. You get it because you have happened to trigger that bug. For this compiler you can report it at Microsoft Connect.
For such a report you need an example with an expected correct result, and the erroneous result.
The following test program compiles & runs nicely with MinGW g++ 5.1
#include <limits>
template<typename T>
constexpr T epsilon = std::numeric_limits<T>::epsilon();
#include <iostream>
using namespace std;
auto main() -> int
{
cout << epsilon<double> << endl;
}
Output:
2.22045e-016
With Visual C++ 2015 update 2 it produces an ICE:
foo.cpp(10): fatal error C1001: An internal error has occurred in the compiler.
(compiler file 'f:\dd\vctools\compiler\cxxfe\sl\p1\c\symbols.c', line 28114)
To work around this problem, try simplifying or changing the program near the locations listed above.
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
foo.cpp(10): note: see reference to variable template 'const double epsilon' being compiled
Compiler version:
> cl /nologo- 2>&1 | find "++"
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23725 for x86
I've raised this as a bug with Microsoft, but they have had a fix since early 2017 which has not been released from what I can see as of today.
I've also provided a project on GitLab and given information to Microsoft for this project here: https://gitlab.com/cppocl/tostring
Loading the .sln and compiling currently crashes with Visual Studio 2015 update 2 or 3, and Visual Studio Enterprise 2017 version 15.3.1.
It does seem that the combination of template and constexpr causes the compiler to crash.
I've seen reports for Visual Studio 2017 describing similar types of problems.
This link says fixed pending release:
https://developercommunity.visualstudio.com/content/problem/18155/msvc-2017-c-fatal-error-c1001-constexpr-initializa.html
Visual Studio 2015 backlog of bugs relating to constexpr is here:
https://blogs.msdn.microsoft.com/vcblog/2015/12/02/constexpr-in-vs2015-update-1/
EDIT:
I also don't believe changing optimization settings will make any difference, as has been recommended in other posts.
I have experimented with these settings and applied recommended patches without success so far.
This constexpr code does not compiled in Visual Studio 2013 version 12.0.21005.1 REL
Is there a newer Visual Studio compiler that works with constexpr?
#include <iostream>
constexpr int factorial(int n)
{
return n <= 1 ? 1 : (n * factorial(n - 1));
}
int main(void)
{
const int fact_three = factorial(3);
std::cout << fact_three << std::endl;
return 0;
}
output from compilation:
1>------ Build started: Project: Project1, Configuration: Debug Win32 ------
1> Source.cpp
1>....\source.cpp(3): error C2144: syntax error : 'int' should be preceded by ';'
1>....\source.cpp(3): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Herb Sutter mentions constexpr on his blog but is unclear in what version it works / will work? http://herbsutter.com/2013/09/09/visual-studio-2013-rc-is-now-available/#comment-13521
Microsoft publishes a C++11 compatibility table, under which constexpr is clearly marked as not being available in Visual Studio 2013.
The November 2013 CTP has it, though.
Source: Google visual studio constexpr
constexpr is not supported in Visual Studio 2013 RTM, see the compatibility table. This is not only true for the RTM version, but also for the Visual Studio Updates.
If you want to stick to Visual Studio 2013, you could download the Visual C++ Compiler November 2013 CTP which comes with some new features, see MSDN blog. Unfortunately Microsoft has no merger with the latest Visual Studio Update features and the CTP features and clearly states that they don't plan to do so.
If we want it all, we need to wait for Visual Studio 2015, see the MSDN blog about VS 2015 Preview.
As is mentioned by the others, November 2013 Customer Technology Preview(CTP) will give you access to constexpr*
Note that just downloading the you'll need to change your "Platform Toolset" to "Visual C++ Compiler Nov 2013 CTP (CTP_Nov2013)" to use the new compiler. You can do that by opening your project's "Property Pages" And going to: "Configuration Properties" > "General" and then changing the "Platform Toolset".
*There is a bit of conflicting information on what portion of constexpr you actually have access to, but it's definitely not all of the standards definition of constexpr. Microsoft says here that the November 2013 CTP adds:
constexpr support (except for constructors)
Microsoft say here that it contains:
constexpr (except for member functions)
I can't even test if it has support for member functions, cause it definitely doesn't have support for any type of constexpr construction. For example this code gives this error with the November 2013 CTP:
error C2127: illegal initialization of 'constexpr' entity with a non-constant expression
One additional note: At time of writing the Visual Studio 2015 Preview still does not support constexpr construction. Keeping my fingers crossed on the final release.
You need to install VS2013 Update 5. (I was on Update 3 and it was not working)
The thing about "Nov 2013 CTP" was inapplicable, as of this writing.
You can do so by going here: https://my.visualstudio.com
and going to download, or :
https://my.visualstudio.com/Downloads?q=visual%20studio%202013
I installed Visual C++ Compiler November 2012 CTP and created a C++ console project. I wrote this in
template<typename T>
void Test(T value){
}
template<typename T, typename... Args>
void Test(T value, Args... args){
Test(value);
Test(args...);
}
int main(){
Test(1,2,3);
}
Then I pressed F6 to build in the IDE. I got this error on line 4
error C2143: syntax error : missing ',' before '...'
The compile list "variadic templates" so I believe this should work. I do understand intellisense may be incorrect however the 'compiler' should work. Can I not build from the IDE? Do I have to enable something somewhere? int i{4}; doesn't seem to work either and I am sure thats valid uniform initialization.
In the Project Properties, make sure to select the Microsoft Visual C++ Compiler Nov 2012 CTP:
The new toolchain does not replace the existing Visual C++ 2012 toolchain, and it is not enabled by default. It's installed side-by-side with the existing toolchain.
If you select the new toolchain, your program will compiler without error.