How do I enable C++11 in gcc?

Question

I use gcc 4.8.1 from http://hpc.sourceforge.net on Mac OSX Mountain Lion. I am trying to compile a C++ program which uses the to_string function in <string>. I need to use the flag -std=c++11 every time:

g++ -std=c++11 -o testcode1 code1.cpp

Is there a way to include this flag by default?

Answer 1

As previously mentioned - in case of a project, Makefile or otherwise, this is a project configuration issue, where you'll likely need to specify other flags too.

But what about one-off programs, where you would normally just write g++ file.cpp && ./a.out?

Well, I would much like to have some #pragma to turn in on at source level, or maybe a default extension - say .cxx or .C11 or whatever, trigger it by default. But as of today, there is no such feature.

But, as you probably are working in a manual environment (i.e. shell), you can just have an alias in you .bashrc (or whatever):

alias g++11="g++ -std=c++0x"

or, for newer G++ (and when you want to feel "real C++11")

alias g++11="g++ -std=c++11"

You can even alias to g++ itself, if you hate C++03 that much ;)

Answer 2

I think you could do it using a specs file.

Under MinGW you could run
gcc -dumpspecs > specs

Where it says

*cpp:
%{posix:-D_POSIX_SOURCE} %{mthreads:-D_MT}

You change it to

*cpp:
%{posix:-D_POSIX_SOURCE} %{mthreads:-D_MT} -std=c++11

And then place it in
/mingw/lib/gcc/mingw32/<version>/specs

I'm sure you could do the same without a MinGW build. Not sure where to place the specs file though.

The folder is probably either /gcc/lib/ or /gcc/.

Answer 3

H2CO3 is right, you can use a makefile with the CXXFLAGS set with -std=c++11 A makefile is a simple text file with instructions about how to compile your program. Create a new file named Makefile (with a capital M). To automatically compile your code just type the make command in a terminal. You may have to install make.

Here's a simple one :

CXX=clang++
CXXFLAGS=-g -std=c++11 -Wall -pedantic
BIN=prog

SRC=$(wildcard *.cpp)
OBJ=$(SRC:%.cpp=%.o)

all: $(OBJ)
    $(CXX) -o $(BIN) $^

%.o: %.c
    $(CXX) $@ -c $<

clean:
    rm -f *.o
    rm $(BIN)

It assumes that all the .cpp files are in the same directory as the makefile. But you can easily tweak your makefile to support a src, include and build directories.

Edit : I modified the default c++ compiler, my version of g++ isn't up-to-date. With clang++ this makefile works fine.