.travis.yml for gcc-5 compiler support on Travis CI

.travis.yml

sudo: required
script:
  - sudo unlink /usr/bin/gcc && sudo ln -s /usr/bin/gcc-5 /usr/bin/gcc
  - gcc --version
addons:
  apt:
    sources:
    - ubuntu-toolchain-r-test
    packages:
    - gcc-5
    - g++-5

Is there a way to do this without sudo?

There is, from https://github.com/richelbilderbeek/travis_qmake_gcc_cpp11 :

language: cpp
compiler: gcc
dist: trusty

Then just use g++ for C++11.

If you really need g++-5 or g++6, use https://github.com/richelbilderbeek/travis_qmake_gcc_cpp14:

language: cpp
compiler: gcc
dist: trusty

before_install:
  # C++14
  - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
  - sudo apt-get update -qq

install: 
  # C++14
  - sudo apt-get install -qq g++-6
  - sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-6 90

I have measured this is faster than using addons

For anybody else's sake: The default g++ in Trusty fully supports C++11 language features, but the libstdc++ that's installed alongside g++-5 is the first that's feature complete for C++11 library features.