I have the following source code. Which compiles fine in visual studios and g++ 3.4.6; but not with g++ 4.4.3 (on a newer ubuntu machine). The newer compiler requires that I explicitly include to use atoi. I am just trying to figure out what might have changed to cause this behavior. Is it sstream header file previously included cstdlib and no longer does so. Or is it the compiler behavior that has changed.
#include <sstream>
int main()
{
char str1[]="123";
int i = atoi(str1);
printf ("value = %d",i);
return 0;
}
You also need to include <cstdio> for printf().
Technically, if you include the headers of the form <cname> instead of <name.h>, you also need to qualify the names from the standard library using std::. A lot of standard library implementations are relaxed when it comes to this, though, and also put the names into the global namespace.
It's implementation-dependent which headers are included by which other headers, so you should always be sure to include all the headers that you need and not assume that they will be included automatically.
I'm using GCC 4.4.5 on Debian, and the headers have changed so you will not bring in the headers necessary. You need to #include <cstdlib> and #include <cstdio> to get atoi and printf, as the compiler complained about both being missing.
#include <sstream>
#include <cstdio>
#include <cstdlib>
int main()
{
char str1[]="123";
int i = std::atoi(str1);
std::printf ("value = %d",i);
return 0;
}
Well yes. That is common. You should always include ALL headers that you are directly using and not depend on the fact that those headers are already included.
Compiler behavior is what would have changed... the <sstream> doesn't use atoi.
Arguably you should have always done #include <cstdlib>, and you'd gotten lucky with your previous compilers.
As James McNeillis points out, you should also #include <cstdio> in order to use the printf function.
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.
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?
I am working on an older project that still has the deprecated "#include iostream.h" inclusions. I understand that iostream.h is deprecated and should not be used, but some of the systems that this code has to run/compile on are old solaris machines running CC and do not have iostream available. My question is: how can I make my more modern g++ compiler accept the iostream.h inclusions.
EDIT: The compilier cannot find the iostream.h file so I am assuming that none of the .h versions of the library are available to g++.
The easiest solution is probably to create a local header file called iostream.h which just includes <iostream> and imports the namespace std. Then, in order for the compiler to allow #include <iostream.h> you add the local path to your include file search path. For g++, this works:
g++ -I local_folder [other flags] …
Incidentally, your remark about
… the deprecated "#include iostream.h"
isn’t quite correct: this isn’t deprecated because it has never been legal C++.
I'd take a step back and write another intermediate header you use everywhere instead that does something like:
#if defined(sun) || defined(__sun)
# if defined(__SVR4) || defined(__svr4__)
/* Solaris */
#include <iostream>
# else
/* SunOS */
#include "iostream.h"
# endif
#else
/* Sane, modern system */
#include <iostream>
#endif
I have created a file called untitled1.cpp in dev-cpp with the following script:
#include <iostream.h>
using namespace std;
int main(){
cout << "C++";
return 0;
}
But the compiler shows errors like:
1 F:\Dev-Cpp\include\c++\3.4.2\backward\iostream.h:31,
from F:\Dev-Cpp\Untitled1.cpp In file included from
include/c++/3.4.2/backward/iostream.h:31, from
F:\Dev-Cpp\Untitled1.cpp 32:2
F:\Dev-Cpp\include\c++\3.4.2\backward\backward_warning.h #warning This
file includes at least one deprecated or antiquated header. Please
consider using one of the 32 headers found in section 17.4.1.2 of the
C++ standard. Examples include substituting the header for the
header for C++ includes, or instead of the deprecated
header . To disable this warning use -Wno-deprecated.
What is the error that I have? How do I fix it?
In C++ you import the standard library without using the .h suffix.
#include <iostream>
So your fixed example:
#include <iostream>
int main(int argc, char **argv) {
std::cout << "C++";
return 0;
}
Your code is not standard C++. You should say #include <iostream> (no ".h"!). Whatever source you have been learning this from is about 25 years out of date, and you should consider getting some more modern material.
(The "iostreams.h" header was part of a very early non-standard library in the early 1990s, and so it's being kept around for "compatibility" reasons, or to catch very inert programmers and give them a helpful hint.)
Use header file as #include<iostream> instead of #include<iostream.h>
Include iostream instead of iostream.h
This is just a warning.
I think that you could try to include iostream instead of iostream.h in order to fix it.
It says that the header, in this case, iostream.h is deprecated or antiquated. (You only have one header, so that's the one! Just read the error message!)
So you'll have to use iostream, not iostream.h.
You've posted the reason in your question already!
This file includes at least one deprecated or antiquated header.
The real question should therefore be: "Which one is antiquated, how do I replace it?", not "What's the error". Answer: Use <iostream>. The <*.h> versions are pre-standard, legacy headers.
So: Read error messages, people.