C++ Error 'nullptr was not declared in this scope' in Eclipse IDE

I am running Eclipse Helios and I have g++-4.6 installed. Hope I am not wrong that g++4.6 implements C++ 11 features. I have created a C++ project which uses the nullptr and auto keywords. The build gives the following errors:-

../{filename}.cpp:13:13: error: ‘nullptr’ was not declared in this scope

../{filename}.cpp:14:2: warning: ‘auto’ will change meaning in C++0x; please remove it [-Wc++0x-compat]

Actually it was building fine until yesterday. I am getting these from nowhere today. Please help me solve this problem.

2012-04-05 17:45
by Vivek Ragunathan

What is the exact version of g++ and what compile options are you using - David Heffernan 2012-04-05 17:48

Please post a code sample that exhibits this behaviour, without that we're trying to read tea leaves here - Timo Geusch 2012-04-05 18:04

I am using g++ 4.6, and imagine lines of code like this:- int* ptr = nullptr; auto x = 123 - Vivek Ragunathan 2012-04-05 18:21

Finally found out what to do. Added the -std=c++0x compiler argument under Project Properties -> C/C++ Build -> Settings -> GCC C++ Compiler -> Miscellaneous. It works now!

But how to add this flag by default for all C++ projects? Anybody?

2012-04-06 11:12
by Vivek Ragunathan

Did you look into Window -> Preferences -> C/C++ -> Build -> Settings - josephthomas 2012-04-06 21:30

I do not have this option sadly - user592748 2013-02-11 00:14

How do I handle this situation with cmake - UserK 2018-02-02 14:38

@UserK in case your compiler is c++11 capable: set (CMAKE_CXX_STANDARD 11)tobilocker 2018-08-02 14:32

According to the GCC page for C++11:

To enable C++0x support, add the command-line parameter -std=c++0x to your g++ command line. Or, to enable GNU extensions in addition to C++0x extensions, add -std=gnu++0x to your g++ command line. GCC 4.7 and later support -std=c++11 and -std=gnu++11 as well.

Did you compile with -std=gnu++0x ?

2012-04-05 17:49
by Rob I

I tried adding -std=gnu++0x and -std=c++0x command line parameters but getting the same problem.

I added it under Project Properties -> C/C++ Build -> Discovery Options -> Compiler Invocation Arguments. Is that the right place - Vivek Ragunathan 2012-04-05 17:59

Probably, but it sounds like the other answer is more grounded in reality. : - Rob I 2012-04-05 18:06

Hi Rob, I noticed one thing now. The IDE does not pick up the compiler argument -std=c++0x although I have added it under Project Properties -> C/C++ Build -> Discovery Options -> Compiler Invocation Arguments. So I tried the command line build 'g++ "../CPP.cpp" -std=gnu++0x -std=c++0x' in a terminal and it compiles fine; produces the binary, which runs successfully. So the IDE does not consider the compiler option specified. The makefile generated does not bear the compiler argument -std=c++0x. Not sure how to force the IDE to consider the compiler argument supplied - Vivek Ragunathan 2012-04-05 18:33

You only need one of the options, and I suggest the -std=c++11or -std=c++0xdepending on your compiler version. Thegnu++0x` enables non-standard extensions - rubenvb 2012-04-05 18:45

Finally found out what to do. Add the -std=c++0x compiler argument under Project Properties -> C/C++ Build -> Settings -> GCC C++ Compiler -> Miscellaneous. It works now!

But how to add this flag by default for all C++ projects? Anybody?

Thanks Vivek Ragunatha - Vivek Ragunathan 2012-04-05 18:58

Is that an actual compiler error or a Code Analysis error? Some times the code analysis can be a bit sketchy and report non-valid errors.

To turn off code analysis for the project, right click on your project in the Project Explorer, click on Properties, then go to the C/C++ General tab, then Code Analysis. Then click on "Use Project Settings" and disable the ones that you do not wish for.

Also, are you sure you are compiling with the C++11 compiler?

2012-04-05 17:48
by josephthomas

Upvoted to counter the downvote. This is almost certainly the problem - Ed S. 2012-04-05 17:51

Thank you. I have run into this issue way to many times, so I thought it was worth mentioning - josephthomas 2012-04-05 17:52

I don't see a code analysis item under C/C++ General tab in my Eclipse project properties. I am using g++4.6. Hope that implements C++11 features, specifically nullptr and auto. Thanks - Vivek Ragunathan 2012-04-05 18:02

Interesting, what version of eclipse do you have? To find out go to Help -> About Eclipse. I am on "Build id: 20120216-1857" and I do not have a problem with seeing it - josephthomas 2012-04-05 18:04

Snapshot of Help -> About Eclipse

Eclipse Java EE IDE for Web Developers. Version: Helios Release Build id: 20100617-1415

Thank - Vivek Ragunathan 2012-04-05 18:06

I am not sure if even have code analysis at all with that build, so that may not be your error. Or it may just be in a different place. I did notice though that is not the version I have. I have the latest from http://www.eclipse.org/downloads/packages/eclipse-ide-cc-developers-includes-incubating-components/indigosr2 . Perhaps if you update you may fix your error - josephthomas 2012-04-05 18:08

OK I noticed one thing now. The IDE does not pick up the compiler argument -std=c++0x although I have added it under Project Properties -> C/C++ Build -> Discovery Options -> Compiler Invocation Arguments. So I tried the command line build 'g++ "../CPP.cpp" -std=gnu++0x -std=c++0x' in a terminal and it compiles fine; produces the binary, which runs successfully. So the IDE does not consider the compiler option specified. The makefile generated does not bear the compiler argument -std=c++0x. Not sure how to force the IDE to consider the compiler argument supplied - Vivek Ragunathan 2012-04-05 18:33

Finally found out what to do. Add the -std=c++0x compiler argument under Project Properties -> C/C++ Build -> Settings -> GCC C++ Compiler -> Miscellaneous. It works now!

But how to add this flag by default for all C++ projects? Anybody?

Thanks Vivek Ragunatha - Vivek Ragunathan 2012-04-05 19:00

@Vivek Ragunathan: Did you look into Window -> Preferences -> C/C++ -> Build -> Settings - josephthomas 2012-04-05 20:28

So, can you please explain if it's possible to introduce nullptr and other keywords to code analyzer or not? I would like to stay with code analyzer.. - sorush-r 2013-05-03 06:04

You are using g++ 4.6 version you must invoke the flag -std=c++0x to compile

g++ -std=c++0x *.cpp -o output

2015-08-11 11:37
by The Beast

Go to Settings -> Compiler... And add flag to "Have g++ follow the coming C++0x ISO C++ language standard [std=c++0x]

2015-12-13 00:48
by Leon

I add the ",-std=c++0x" after "-c -fmessage-length=0"，under Project Properties -> C/C++ Build -> Settings -> GCC C++ Compiler -> Miscellaneous. Dont't forget to add the comma "," as the seperator.

2016-07-09 06:40
by qie

Trying with a different version of gcc worked for me - gcc 4.9 in my case.

2018-03-09 11:18
by JobJob