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

54
votes

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.

7
c++g++eclipse-cdt
What is the exact version of g++ and what compile options are you using? – David Heffernan
Please post a code sample that exhibits this behaviour, without that we're trying to read tea leaves here. – Timo Geusch
I am using g++ 4.6, and imagine lines of code like this:- int* ptr = nullptr; auto x = 123; – Higher Kinded Type

7 Answers

57
votes

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 ?

21
votes

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?

6
votes

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

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

4
votes

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?

3
votes

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

0
votes

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.

0
votes

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