Recently I have being working on a project using C++ as the programming language and Eclipse CDT as the programming IDE. The 'Chrono' library is used in the project.
I was trying to define the "<<" stream operator for different time scales like nanoseconds by putting the definitions in the same namespace as chrono, namely "std::chrono". One small example of the code of the header file (Test.hpp) is illustrated as following:
#include <chrono>
#include <iostream>
namespace test{ namespace chrono{
typedef std::chrono::nanoseconds nanoseconds;
}}
namespace std{ namespace chrono{
inline std::ostream& operator<<(std::ostream& s, nanoseconds dur)
{
return s << dur.count() << "ns";
}
}}
The above code together with other parts of the project can be compiled correctly. However, the IDE, Eclipse CDT, keeps complaining "Type 'std::chrono::nanoseconds' could not be resolved" and the auto-completion functionality says "No Default Proposals" for any member variables/functions in the namespace "std::chrono". It looks like that adding new functions into the "std::chrono" namespace in this header file somehow 'hides' other content from the Eclipse's point of views.
The question is what could be the reason leading to such 'error' messages in Eclipse CDT or it is one flaw in my programming? I would appreciate any help or hint from you.
I also copy-past the code into Xcode on the laptop and there is no such error message as in Eclipse CDT.
Additional information:
The os I am using is Mac OS, thus the chrono library is slightly different from that mentioned in the answer. The screenshot of 'chrono.hpp' is as following:
Actually, my CDT has no issue to find the members in the namespace 'std::chrono::'. What confuses me is CDT's behaviour when I add/override members in the namespace 'std::chrono::'. See the following pictures:
Errors appear when I override a member function in the namespace:
Errors do not appear when I do nothing on the namespace:
Any idea on how to solve this problem?
Assumptions about your setup
I believe you have changed your build settings to use -std=c++0x or something similar as the chrono library requires it.
Perhaps you did it like this:
At the top of chrono (header file) there is a bit like this:
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
so that if you don't have sufficiently new C++ standard, you get a compile error.
Now the problem is the CDT indexer that is used to generate highlighting and code completions does not know you are using __cplusplus >= 201103L. You can see this in this following screenshot that the majority of chrono is inactive because __cplusplus is the wrong value.
This screenshot shows the incorrect value and the errors CDT identifies:
And if you try and code complete, you get the wrong thing too:
How to fix it
To fix the problem, you need to tell CDT that your project uses GCC settings that are different from the default GCC settings. i.e. because of the different standard __cplusplus in particular has the wrong value.
In Project Properties, choose C/C++ General -> Preprocessor Includes and then the Providers tab.
Choose the CDT GCC Built-in Compiler Settings
Uncheck the Use global provider shared between projects
Press OK
Here is a screenshot of what that looks like:
Once you do this, you should see that chrono's inactive sections becomes correct in the editor:
But your source file may still be wrong. You should then rebuild the indexes to update, right-click on the project, choose Index -> Rebuild:
Finally your code should not display properly:
And the code complete should be working too!
History
This is a case where CDT's right hand and left hand don't agree. Historically I believe the reasoning for this is down to performance and trading off indexing every possible variant of compiler/user option, vs having some shared data across the workspace that may be wrong for some projects.
Related
I try to run codes like
#include <string>
#include <iostream>
int main() {
std::string str = "This is a string";
std::cout << str.starts_with("name");
}
But intellisense will give out an error
"std::__cxx11::basic_string<char, std::char_traits,
std::allocator>" has no member "starts_with" C/C++(135) [6,9]
And It still can be build and produce a correct result.
Also it can find implementation in header file.
But the macro __cplusplus is defined as 201703L
I've already added a command -std=c++20 when building, why this happened?
Compiler: minGW 11.2 compiled by msys2
Assuming you are using Microsoft's C/C++ extension, you must configure the extension to use C++ 20 standard for intellisense.
The easiest way to do this is to add the line "C_Cpp.default.cppStandard": "c++20" to your settings.json file. You can also find the setting in the GUI under the name "Cpp Standard". Selecting c++20 from its dropdown will achieve the same result.
Note that this setting is, by default, set as a global user defaults. You can configure it per-workspace by selecting the Workspace tab in the settings GUI and changing that Cpp Standard dropdown to c++20.
As for why adding the -std=c++20 flag didn't work: -std=c++20 just tells your compiler which standard to use to build your code. 'Intellisense' does not receive this flag because it is a separate tool from the compiler and is therefore not required to support all the standards the compiler supports. It may support less even, although Intellisense tools usually support as current a standard as possible. Therefore the language standard for Intellisense must be configured separately from the compiler (in this case).
Final Note: After changing the setting, try closing and re-opening VS Code. In my experience changing the language standard setting can cause some weirdness to happen. Closing and re-opening VS Code seems to ensure the setting changes take full effect.
I have written a program using C++11 features.
/* * test.cpp * * Created on: 05-Jul-2015 * Author: avirup */
#include<vector>
#include<iterator>
#include<iostream>
using namespace std;
int main() {
vector<int> v;
v.push_back(5);
v.push_back(7);
for(auto i=v.begin();i!=v.end();i++) {
cout<<*i<<endl;
}
for(auto i=v.cbegin();i!=v.cend();++i) {
cout<<*i<<endl;
}
}
The program is compiling correctly and showing results but the editor is showing but red lines below valid functions like cbegin() and cend() which are constant reference iterators. which is annoying. How to get rid of this?
Just for completeness since this has no answer and give an explanation.
To achieve compiling with C++ 11 (or another version) and Eclipse actually supporting it you need to do two things.
First the compiler flag needs to set so -std=c++11 or -std=c++0x is appended when calling g++ or whatever is used.
Open the properties for the properties for the project. Select it and right click ↦ Properties (or Alt+Enter for Windows users)
Go to C/C++ Build ↦ Settings, maybe select your preferred configuration, ↦ GCC C++ Compiler (or any other compiler you use) ↦ Dialect.
Select from the combo or write the flag to the Other dialect flags if not present in the combo (like -std=gnu++14 or -std=c++1z).
CDT will now call your compiler with -std=c++0x when compiling. Now to the part so CDT supports C++11 and does not show errors for missing types and such. My libstdc++ contains lines like
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else // C++0x
that causes your errors and the actual type declarations/definitions are greyed out if you view them in the C/C++ editor. __cplusplus needs to be set correctly with #define __cplusplus 201103L so they will be parsed and indexed by CDT. This is also done via the project settings or can also be done for the whole workspace.
Go again to the project settings.
C/C++ General ↦ Preprocessor Include Paths, Macros etc., also maybe select your preferred configuration, ↦ tab Providers.
Select the entry for your compiler (for me it’s CDT GCC Built-in Compiler Settings MinGW.
Add -std=c++11 or -std=c++0x to the Command to get compiler specs textfield at any location.
Optional: Select Allocate console in the Console View and hit apply. You should now see something like #define __cplusplus 201103L in the console.
To set it for the whole workspace just check Use global provider shared between projects and click on Workspace Settings where an almost identical dialog opens.
I’m currently writing a plug-in that extends the new C/C++ project wizard where one can select the C++ version for the project that sets the compiler flag correctly and also the above setting for the indexer and some other stuff. But dunno if it will ever will be integrated into CDT or needs to be installed via plug-in. But it sure will be in https://www.cevelop.com in a few months.
My program compiles fine, but Netbeans tells me "Unable to resolve identifier to_string."
I tried everything in "Netbeans 7.2 shows "Unable to resolve identifier" , although build is successful" and I set the "C++ standard" to "C++11" in the code assistance options.
This is the only function giving this problem so far. It is however also the first C++11 feature I am using, which leads me to believe it has something to do with Netbeans not understanding that I am using C++11, although I specify it explicitly in the code assistance menu.
Minimal example:
#include <string>
int main() {
std::to_string(1);
}
EDIT: the same problem arises where using nullptr
EDIT2: I suddenly realized it might be important to mention that I do not use a generated Makefile, but SCons.
I know this question is seven months old but since it came up as the second result to a google search I'll tell the answer I came up with. For Netbeans at least. Go to your project properties and make sure you have you "C Compiler"->"C Standard" set to C11, and your "C++ compiler"->"C++ Standard" set to C++11. You have to set BOTH or it will still give false errors!
This will solve the problem:
Right click on "Project".
Select "Code Assistance".
Clean C/C++ cache.
Restart IDE.
Autocomplete and sometimes even syntax highlighting are always faulty with C++. The more you go in depth with C++ and C++11, the more Eclipse and Netbeans will start underlining everything with a red wavy line. Some of my (correct and perfectly compiling) programs are a huge red wavy line. I suggest you disable error markers altogether and you keep autocomplete, but in many cases it just won't work and you have to make the best of it.
I had the same situation. This was occurred because I used .c file instead of .cpp
for Netbeans 8.2 (on Linux) only the following worked for me: Tools -> Options -> Code Assistance -> Macro Definitions:
change:__cplusplus=199711L
to:__cplusplus=201402L
for C++14
or to __cplusplus=201103L
for C++11
I did all the above but what did the trick for me was recognizing that the Makefile had g++ rather than g++ -std=c++11.
To resolve c++17 related 'Unable to resolve identifier' in latest netbeans 8.2 or 9 version, one may need to set the macro definition __cplusplus=201703L as the default C++14 standard macro definition unable to resolve those unexpected error messages appeared in the editor.
I am a beginner was trying to do some C++ programming on Xcode. It works fine, but when I try to compile the same c++ file on my windows pc using VS, there were some errors. After I look at my code closely, there are really some stupid mistakes that I have made which caused the errors, but Xcode seemed to have ignored them...
My question is that is there any setting that I need to change to prevent Xcode from being so smart?
For example, the following code can actually compile in xcode:
#include <iostream>
using namespace std;
int main() {
if (true or false){
cout << "How is this possible? \n";
}
return 0;
}
There are also other cases where the code is actually wrong, but it can compile just fine is Xcode which is the annoying part and I want to disable that.
As far as I can see there is nothing wrong with your code.
The ISO C++ standard does not specify which standard headers are included by other standard headers. So, it is entirely possible that the version of iostream used by Xcode directly or indirectly includes ciso646. Whereas Visual Studio's version of iostream does not include ciso646. There are many similar cases with other headers. You just need to read the error messages and realize that your error (when you move your file to a different platform) is due to a missing header file.
It would be nice if writing portable code meant writing code in accordance with the C++ standard specification, but unfortunately that's not the case. Although there are various compiler options on various implementations which can help bring different implementations closer together, in general you will just have to bring the code into the target environment and actually test it there.
So ultimately writing portable code means you'll have to learn some subset of C++ that is accepted by all the implementations you want to target.
or is an 'alternative token' in C++, and VS is incorrect to reject it. There's no option in Xcode to disable support for alternative tokens. However VS has non-standard support for or as a macro using the header <ciso646>, and Xcode does have a header <ciso646> which does nothing (as the standard specifies). So you can write code which uses or and which works in both Xcode and VS by including this header.
#include <iostream>
#include <ciso646> // does nothing in Xcode, allows `or` in VS
using namespace std;
int main() {
if (true or false){
cout << "How is this possible? \n";
}
return 0;
}
Unfortunately VS can't support all of the alternative tokens through macros and so Xcode will still support some that VS doesn't.
There are also other cases where the code is actually wrong, but it can compile just fine is Xcode which is the annoying part and I want to disable that.
If you give specific examples then I can provide additional advice on how to write portable code.
Rather than changing your Xcode settings, I suggest cross-checking your code using another development environment.
If you're looking for something cheap and full-proof. Download a VirtualBox Windows VM, and run download Dev C++ (bloodhshed)
VS does not support or: you need to use || instead.
You can include some special files but it doesn't inject or sufficiently well into the language for it to work in all instances.
If you want to suppress use of or (and your compiler supports no better way)
#define it to something that emits a compiler error, for example
#define or OR
This at least means that the nature of the compilation errors will be identical on Xcode and VC.
I've recently started diving into the code of an open source project, which is largely written in C++. I'm using Eclipse 3.8 in Ubuntu 12.10.
THE PROBLEM:
Eclipses is incorrectly flagging fields as unresolved because of a particularly elaborate convention used to separate field declarations out of the header files.
someclass.h
class SomeClass
{
public:
#define MACRO_CLASS_PARAM(Name) SomeType m_##Name;
#include "fields.h"
#undef MACRO_CLASS_PARAM
};
fields.h
MACRO_CLASS_PARAM(Field1)
MACRO_CLASS_PARAM(Field2)
...
Now in the cpp file, if I want to do something like instanceOfSomeClass.Field1 Eclipse will flag it as an error with "Field 'Field1' could not be resolved".
THE QUESTION: Is there any way to get Eclipse to correctly handle this situation?
The inability to correctly process #include statements that are not at global scope is a long-standing deficiency in Eclipse's indexer.
Things you could do about it:
Revise your code to avoid this pattern. Once the textual header inclusion model is superseded by C++ Modules, it's going to be invalid anyways.
Contribute a fix for this deficiency to Eclipse CDT.
Use a different IDE that can parse this pattern. (I don't know of one off the top of my head, but I also haven't spent a lot of time looking.)