The following code compiles fine with Visual Studio 2013 (probably because <iostream> includes <limits>), but the "missing" #include <limits> prevents me as C++ newbie sometimes to understand whats going on. For example I realized that std::numeric_limits<int>::max() is in <limits> only after removing #include <iostream>.
So how can I force the compiler to require each include explicit?
#include <iostream>
int main() {
std::cout << std::numeric_limits<int>::max();
}
While this isn't a compiler "Warning" per say, you can have the MSVC compiler output a list of all included files at compile time with the /showIncludes flag MSDN compiler reference
Related
I am using Visual Studio Community 2017 to code c++. When I run the following code everything works fine.
#include "pch.h"
#include<Windows.h>
#include<Psapi.h>
#include <iostream>
#include <conio.h>
int main()
{
std::cout << "Really!! How do you do it?";
_getch();
}
But if I change the order of #includes by including psapi.h before Windows.h, compiler goes badass and throws 198 errors at me, which surprisingly(maybe only to me) includes Identifier "BOOL" is undefined.
Why is this happening?
Since Psapi.h's include tree is trivial, I'm going to exemplify. Everything relies on VStudio 2015 (Community) (v14.0.25431.01 Update 3) and Windows Kits 8.1 (? funny, because v10 is there too) files (with default env vars and preprocessor definitions):
BOOL is defined in minwindef.h (#157: typedef int BOOL;)
Psapi.h only includes one file (#27: #include <winapifamily.h>)
winapifamily.h doesn't include any other file
So, when reaching Psapi.h (#87: BOOL WINAPI EnumProcesses (...), the compiler doesn't know anything about BOOL, so it complains.
Windows.h includes minwindef.h (indirectly, via windef.h), and that's why it works when you include it before Psapi.h.
Personally, I think it's a bug in Psapi.h, since it's not self contained, but there might be a good reason (that I'm not aware of) for that. Anyway, if this is indeed a bug, it wouldn't be MS's 1st one :)
#include <Windows.h>
#include <WinSock2.h>
// main present just for rigorosity's sake
int main() {
return 0;
}
to answer the question, I know this is DATED but the issues persist today. You need the following:
#include "stdafx.h"
#include <stdbool.h>
#include <Windows.h>
#include <stdlib.h>
#include <psapi.h>
After stdlib.h was included, the errors were gone.
I noticed that clang++ includes a missing header - <limits> on Mac, while g++ shows errors about it on Linux. Now I wonder why clang does it, and gcc not. And how I can force clang to not do it.
Here is a sample code which compiles by clang on Mac, but not by gcc on Linux:
#include <iostream>
using namespace std;
int main()
{
cout << "int max: " << numeric_limits<int>::max() << endl;
}
UPD
I looked into libraries and here is what I found.
Internally <iostream> includes <istream>, which defines >> operator for different types. <istream> wants to know limits for short, int and streamsize types.
clang++ uses libc++ standard library, which uses std::numeric_limits class template from <limits> in <istream> for this purpose. That's why this header is included automatically when <iostream> is included.
g++ uses libstdc++ standard library, which uses __gnu_cxx::__numeric_traits class template from <ext/numeric_traits.h> instead of using <limits> in <istream> (<bits/istream.tcc>). There is also a comment in that header which explains why they don't use <limits>:
<limits> is big and we avoid including it
Used compilers:
> clang++ --version
Apple LLVM version 8.0.0 (clang-800.0.42.1)
$ g++ --version
g++ (Debian 4.9.2-10) 4.9.2
In C++, unlike C, standard headers are allowed to #include other standard headers. That sometimes leads to mysterious errors like the ones you're seeing: one compiler's <iostream> includes <limits> and the other doesn't. The solution is to always include the headers needed for whatever names you use. In this case that means to #include <limits> in your code, even though it compiles okay as is with one compiler. There's no harm in #include a header that's already been pulled in, so that's okay with both compilers. It's annoying sometimes, but that's just the way things are.
The clang version of the <iostream> header likely #includes the <limits> header, as such you get it automatically as part of #includeing the <iostream> header.
There's nothing you can do about it. That's how that compiler's library is implemented. You can simply add
#include <limits>
to this file, and it should compile on both platforms.
My code works well without #openmp
but I got this error when I added #openmp compiler
1>c:\users\hdd amd ali\documents\v studio 10 projects\visual studio 2010\projects\escaledesvols2 - copy\escaledesvols2\djikstra.cpp(116): fatal error C1001: An internal error occurred in the compiler.
1> (compiler file 'f:\dd\vctools\compiler\utc\src\p2\wvm\mdmiscw.c', ligne 1098)
note:
i use many different libraries (like #boost)
#include <string>
#include <iostream>
#include <stdio.h>
#include <ctime>
#include <iomanip>
#include <sstream>
#include <msclr\marshal_cppstd.h> // for unmanaged piece of code
#include <vcclr.h>
I had this issue recently; I was compiling with visual studio 2015. I tried it with visual studio 2017 and I still got the internal compiler error. Then I tried it with visual studio 2013 and it told me that I can't have a "return" statement inside an openMP section. when I removed the return from VS 2013 and VS 2105 the compiler was able to successfully compile. So, it make sense to try it with VS 2013 and it will give you a better error description. You could also be having return statements inside openMP sections and that could be the reason for c1001 error.
In my case it was a return function from the OpenMP loop. Removing a "return" line solved the problem.
You should simply report it.
In terms of workarounds, it is likely related to memory/resource consumption. Usual tricks to lower consumption are
disable debug information
split up compilation units to smaller size (this might be key here: "I'm using many libraries" should not be an issue unless you're including all the headers in a single translation unit
try to reduce template instantiations
Alternatively
reduce system load (close other programs, such as your Stackoverflow browser that might tatke valuable resources :))
So, I have this question. Why does cout throws
error C2065: 'cout' : undeclared identifier
I am using Visual Studio 2012 as an IDE and I am writing a school project. I have everything done except an example file. So I am trying to write something on the screen like this:
#include "iostream"
#include "stdafx.h"
using namespace std;
int main()
{
cout<<"example";
return 0;
}
So the problem is with cout... printf works fine, but I want to use cout.
EDIT:
I've changed "" to <> but it is not helping. Also I am using this code only for example... This is not the whole project.
stdafx.h shall be the first include directive in your source file.
Switch files and convert the second include to <>, as other suggested.
#include "stdafx.h"
#include <iostream>
See this post for more information.
First of all:
#include <iostream>
instead of #include "iostream"
Secondly, it is generally considered bad practice to write using namespace std;, even though most courses start with that. It is better to only use what you actually need, in your case:
using std::cout;
#include "iostream"
should be
#include <iostream>
Quoting from this post:difference-between-iostream-and-iostream-quotes-in-include
By courtesy of #Jerry Coffin's answer:
When you use < >, the compiler only looks in the system-designated directory/directories (e.g., whatever you've set in the include environment variable) for the header.
When you use " ", the compiler looks in the local directory first, and if that fails, re-searches just like you'd used < >. Technically, (i.e., according to the standard) that doesn't have to be the "local" directory, but that's how it works in essentially every compiler of which I'm aware).
EDIT:
However, the root cause is that stdafx.h is a precompiled header. Visual C++ will not compile anything before the #include "stdafx.h" in the source file, unless the compile option /Yu'stdafx.h' is unchecked (by default); it assumes all code in the source up to and including that line is already compiled. However, it is still better to use <> with iostream not to confuse reader of the code.
If you use #include <iostream> with the <> instead of "" then it should work. Right now, the compiler doesn't know where to find the iostream library.
Also, you might want to change cout<<"example"; to cout<<"example"<<endl; for a new line so that it formats correctly.
Came across this issue while trying to build a Dynamic Linked Library. Make sure that instead of the #include stdafx.h you specify the following include on the first line of your .cpp file:
#include "pch.h"
This should also be the case for VS2017 or earlier.
This error also occurred in the Visual Studio 2017 IDE. Moving stdafx.h to the top solved the error.
For more on stdafx.h, see What's the use for "stdafx.h" in Visual Studio?
When compiling the following source:
int main()
{
exp(1.0);
return 0;
}
the copiler gives the following error: error C3861: 'exp': identifier not found because I didn't have the line: #include <iostream> above main()
However, visual studios won't display the error if a library is indirectly included. For example, the following code compiles without a problem even though the dependency of exp is in <cmath>.
#include <istream>
int main()
{
exp(1.0);
return 0;
}
This is because <iostream> includes <istream> which include <ostream> which includes <ios> which includes <xlocnum> which includes <cmath>.
Is there a way to make visual studios throw an error if I don't explicitly include a library yet try to use one of its identifiers?
You may want to have a look at include-what-you-use. It is a clang-based tool trying to detect missing and superfluous include directives.