The code I am writing is throwing this error:
'optional': is not a member of 'std'
I understand that the file <optional> is located in MSVC/tools and this external dependencies section is usually populated by Intellisense, but the file appears not to be included even though I confirmed that the file does indeed exist and I have #include <optional>.
What is the best way to close the gap here?
Is there a way to tell Visual Studio to include all the MSVC tools?
Code snippet from header:
#pragma once
#include Examples.h
#include <optional>
#include <vector>
namespace Samples
Code snippet from cpp:
#include 'Examples.h'
std::optional<Samples::Matrix> Samples::TestFunction()
You must have your C++ Language Standard option in Project Settings set to C++17 or later:
Right-Click on the project in the Solution Explorer
Select Properties
Under Configuration Properties > General > C++ Language Standard
Select ISO C++17 Standard (/std:c++17) or Preview Latest (/std:latest)
Future readers: ISO C++20 Standard (/std:c++20) is also an option.
Click OK
Save All to save the changes to the project.
Related
I am trying to get the system ID using
auto info = winrt::Windows::System::Profile::SystemIdentification::GetSystemIdForPublisher();
auto id = info.Id();
auto asHex = winrt::Windows::Security::Cryptography::CryptographicBuffer::EncodeToHexString(id);
But when I try to run this code I get errors E0035 and C1189 and both have the exact same description:
The <experimental/coroutine> and <experimental/resumable> headers are only supported with /await and implement pre-C++20 coroutine support. Use coroutine for standard C++20 coroutines.
(Note: the italic coroutine above is inside <>, as soon as I put <> around the a word it disappears so I have omitted it)
I am including all the relevant files in my header that I think might be needed:
#include <Windows.h>
#include <coroutine>
#include <windows.foundation.h>
#include <winrt/Windows.System.Profile.h>
#include <winrt/Windows.Security.Cryptography.h>
I am using:
Microsoft Visual Studio Community 2019
Microsoft Visual C++ 2019
Windows 10 SDK 10.0.19041.0
In your project, if you go to
Property Pages ->
Configuration Properties ->
General ->
C++ Language Standard,
do you by any chance have it set to "ISO C++20 Standard (/std:c++20)"?
C++/WinRT only runs C++17.
A few hours ago I realized that C++/WinRT exists, and I am currently trying understand the fundamentals of it. If my memory serves me correctly, I also got this exact error message when trying some not-at-all-copy-pasted-from-msdn code out. Although I am using Visual Studio 2022 (Community Edition), I do not see why that would make a difference.
I hope this is of any use.
Kind regards,
a not so experienced programmer
I coded in C++ on Visual Studio (Windows 10) and got this error:
#error The <experimental/filesystem> header providing std::experimental::filesystem is deprecated by Microsoft \
and will be REMOVED. It is superseded by the C++17 <filesystem> header providing std::filesystem. \
You can define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING to acknowledge that you have received this warning.
With this headers:
#include <iostream>
#include <fstream>
#include <string>
#include <windows.h>
#include <filesystem>//If I will disable it nothing happens.
#include <experimental/filesystem> //If I will disable it happens another error.
namespace fs = std::experimental::filesystem;
using namespace std;
I've tried: #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING in the main cpp file. It didnt help.
So then I paste this code from here:
#ifdef __cpp_lib_filesystem
#include <filesystem>
using fs = std::filesystem;
#elif __cpp_lib_experimental_filesystem
#include <experimental/filesystem>
using fs = std::experimental::filesystem;
#else
#error "no filesystem support ='("
#endif
Didn't helped too.
What is the easiest way to get out that error?
Add _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING to Preprocessor definitions.
Project -> Properties -> C/C++ -> Preprocessor -> Preprocessor Definitions.
This solved the issue for me.
According to the link
C++17’s is supported. This is a completely new
implementation, incompatible with the previous std::experimental
version, necessitated by symlink support, bug fixes, and changes in
standard-required behavior. Currently, including provides
the new std::filesystem and the previous
std::experimental::filesystem, and including
provides only the old experimental implementation. The experimental
implementation will be REMOVED in the next ABI-breaking release of the
libraries.
MS abandoned 'experimental' in filesystem.
You could try to use #include <filesystem>instead of #include <experimental/filesystem> and the std::experimental::filesystem is slated for removal, this means you should use std::filesystem.
I had the same problem and then, when I removed the experimental filesystem and added:
#include <filesystem>
namespace fs = std::filesystem;
I would get the error:
namespace “std” has no member “filesystem”
The solution was to go to project properties and do as instructed in the link.
VS2017: E0135 namespace "std" has no member "filesystem"
Adding the define where necessary worked for me:
#define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING 1;
ie.
#ifdef __cpp_lib_filesystem
#include <filesystem>
namespace fs = std::filesystem;
#elif __cpp_lib_experimental_filesystem
#define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING 1;
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
#else
#error "no filesystem support ='("
#endif
I've been researching this same problem for weeks, and I'm using visual studio 2019 on an Unreal Engine 4 project. It's difficult to enable c++17 headers in visual studio and make them work. A lot of people online suggests using the boost library instead, but this is my attempt in using filesystem because I don't want to deal with trying to download / import external libraries, and so here's what I know...
** Before you start coding in visual studio, you should build / compile your project and see if Visual Studios needs anything set up; for me, I had to download / setup a free license with Incredibuild (there are tutorials online if someone needs to get this setup). Incredibuild is helpful and necessary to build projects in Visual Studio (at least if you're using Unreal Engine 4), but sometimes I get 1 or 2 "errors" in visual studio, but will compile in Unreal Engine 4 because those errors aren't actually errors (people say online that Incredibuild is weird, and wanted to mention that)**
1) How to enable c++17 Headers
When trying to #include which is a c++ version 17 header, it's necessary to enable c++17: Look inside the visual studio "solution explorer" to view the project files, and right-click the project itself and open "properties". Go to the "C/C++ language" tab and switch the version to c++17 (this is easy to find this online). Unless you're doing an Unreal Engine project because there is not a "C/C++ language" tab, so instead find the "NMake" tab and in the text-box to the right of "Addition Options" type in:
/std:c++17 OR /std:c++latest (Microsoft has a list I found online of others, but these are fine)
and visual studios will recognize as a header.
2) How NOT to get c++17 namespaces to work (things I've tried)
After the headers start working you can try to finally make a namespace variable:
namespace fs = std::filesystem; => ERROR: 'std does not have a namespace or class filesystem'
OR if you also #include you can try:
namespace fs = std::experimental::filesystem; OR namespace fs = std::experimental::filesystem::v1; => ERROR: 'we want you to define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING'
how does one fix these errors?
Online, I found that adding these lines of code to your ProjectName.Build.cs file (which can be found and edited after clicking on the file in "solution explorer") instead of the original declaration for PCHUsage:
PCHUsage = PCHUsageMode.NoSharedPCHs; PrivatePCHHeaderFile = "Folder.h"; CppStandard = CppStandardVersion.Cpp17;
this did get rid of the Errors when using std::filesystem BUT caused wayyyy more problems, and seemed harmful. After looking through other websites / possible solutions, it seems people online don't know how to actually use the filesystem library in visual studio, I've been looking for working code for weeks.
if you want to try and use the std::experimental::filesystem or std::experimental::filesystem::v1, I tried #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING, but no dice.
I'm in the same boat as you man, and it looks like you didn't get much help from the previous comments. If we can't find a solution / video tutorial online, I have a plan B. Maybe we could try and write a c++17 project using some different software, or maybe we could write a program using a different software that could be launched instead of enabling c++17 into Visual Studio; for example, if you wanted to list the files in a directory, make an executable file in your preferred other software, and launch that executable / feed it arguments from your visual studio project. That's the best I got man. I hope that sparks some creativity or whatever, but I think it's a lot more helpful than what I've seen online. Good luck to you! and I need that luck too
I am using visual studio 2017 and I have run across a problem. When trying to use std::gcd it gives me an error error C2039: 'gcd': is not a member of 'std'
Here's my code:
#include "pch.h"
#include <iostream>
#include <numeric>
int main() {
std::cout << std::gcd(10, 5);
return 1;
}
std::gcd was added in C++17. To use it in Visual Studio you need to specify the language standard. You can do that two ways, use the /std:c++17 command-line option or in the Project Properties dialog: C/C++ -> Language -> C++ Language Standard.
I just tested and got the same error with VS2017 15.8.9 after having set the language standard to C++17. When I checked my project settings again, the language setting I made had reverted back to the default. After having set it a second time, it worked.
This seems to happen often when I start a new project and change to C++17 directly.
i have installed OpenCV 3.10 and the linked the opencv_world310.lib to release and opencv_world310d.lib to debug.
Moreover I put the compiler options in search directory to ...opencv\build\include. I got a undefined reference error when i left out #include <opencv2/highgui.hpp. Now that i have included it my code looks like this:
#include <stdio.h>
#include "opencv/cv.h"
#include "opencv/highgui.h"
#include <opencv2/highgui.hpp>
int main(void){
printf("HALLO!");
return 0;
}
When i try to build it core.hpp opens and the error: core.hpp must be compiled in C++ occurs.
I am using the GNU GCC Compiler in Codeblocks.
What should i do to solve the problem?
Check you compiler options. Open CV 3.10 C++ API requires code to be compiled as C++, but not C. You can use answer to "CodeBlocks: change project language c and c++" question to change the options.
Also use the new Open CV 3.10 API
#include <opencv2/opencv.hpp>`
instead of all the other Open CV header files. This header includes core functionality. To enable highgui module you need to define HAVE_OPENCV_HIGHGUI in your project settings.
I am trying to build a C++ app that uses both websocketpp and MySQL. I have encountered 2 build problems using VS 2010 C++ Express.
1) A problem with the boost libraries. It produces many errors like this:
1>c:\program files (x86)\boost\boost_1_50\boost\thread\win32\thread_data.hpp(210): error C2146: syntax error : missing ')' before identifier 'rel_time'
Here's the relevant snippet from thread_data.hpp starting with line 210:
inline BOOST_SYMBOL_VISIBLE void sleep(TimeDuration const& rel_time)
{
interruptible_wait(detail::pin_to_zero(rel_time.total_milliseconds()));
}
2) A conflict with the word VERSION which is documented here and I believe is independent.
To make a clear and simple example of the boost build problems, I'm using the websocketpp example: echo_server.cpp to which I added these includes:
#include "stdafx.h"
Boost lib includes recommended by "Building a program with websocketpp" on the websocketpp site.
#include <boost/regex.hpp>
#include <boost/random.hpp>
#include <boost/system/api_config.hpp>
#include <boost/system/config.hpp>
#include <boost/system/error_code.hpp>
#include <boost/system/system_error.hpp>
#include <boost/system/windows_error.hpp>
and the MySQL header includes. Adding these 2 boostincludes triggers the build errors. If I comment out these 2 includes, it builds without errors:
#include <my_global.h>
#include <mysql.h>
Any suggestions on how to deal with the boost problems?
I don't think this is the same build problem as this one, "Trying to build websocket++ with MinGW: last few linker errors — what could it be?"
Concerning the first error, check if there are any macros interfering with the code. Right-click and go to definition or #define the macro yourself at the beginning of the file and see where it gets redefined. In really hard cases, look at the preprocessor output via a compiler flag.
Concerning the rest, you don't provide any versions for Boost and MySQL. Then, there is my_global.h (or is that part of MySQL?) and stdafx.h, which are both under your control but you don't show them here. Also, try to reduce the issue to the smallest possible piece of code. In short, provide a reproducible example.