How to use travis-ci to build modern c++ using modern cmake? - c++11

Question

Is it possible to use travis-ci to build a c++ application/project that uses cmake, gcc-6 and g++-6?

Answer 1

Configuring travis to use the right compiler is a bit tricky.
This is how it can be done:
First of all you need to set the distribution to trusty (the newest version of ubuntu that's supported by travis-ci) and require sudo.
dist: trusty
sudo: require
Next up we set the language and the compiler:
language: cpp
compiler: gcc
So far so good. Now we can go about setting up the apt install configuration:
addons:
apt:
sources:
- ubuntu-toolchain-r-test
packages:
- gcc-6
- g++-6
- cmake
This adds the ppa for the newer version of our build tools and installs them. The next step is setting up links to the new gcc and g++. /usr/local/bin is being searched before /usr/bin, so that our newly installed version 6 compilers are going to be accessible with just gcc and g++. The beginning of your script: should look like this:
script:
- sudo ln -s /usr/bin/gcc-6 /usr/local/bin/gcc
- sudo ln -s /usr/bin/g++-6 /usr/local/bin/g++
Add the next line as well, if you want to verify the versions of those tools:
- gcc -v && g++ -v && cmake --version
The versions that come back from these commands are as follows:
gcc: 6.2.0
g++: 6.2.0
cmake: 3.2.2
That's basically it. The complete .travis.yml looks like this:
dist: trusty
sudo: required
language:
- cpp
compiler:
- gcc
addons:
apt:
sources:
- ubuntu-toolchain-r-test
packages:
- gcc-6
- g++-6
- cmake
script:
# Link gcc-6 and g++-6 to their standard commands
- ln -s /usr/bin/gcc-6 /usr/local/bin/gcc
- ln -s /usr/bin/g++-6 /usr/local/bin/g++
# Export CC and CXX to tell cmake which compiler to use
- export CC=/usr/bin/gcc-6
- export CXX=/usr/bin/g++-6
# Check versions of gcc, g++ and cmake
- gcc -v && g++ -v && cmake --version
# Run your build commands next

Answer 2

I found some errors in #henne90gen's answer (or maybe they've just changed). Specifically:
You don't need sudo.
You don't need to install CMake from apt. This will install an ancient CMake 2.8 from Trusty. Fortunately the build image already comes with CMake 3.9.2 (as of now).
gcc-7 doesn't get installed to /usr/local/bin and it is already in the PATH.
This should work:
dist: trusty
language: cpp
addons:
apt:
sources:
- ubuntu-toolchain-r-test
packages:
- gcc-7
- g++-7
script:
- export CC=gcc-7
- export CXX=g++-7
- ...
Here's a longer example that includes a modern version of Qt (with QtSVG which I'm using), and works on OSX and Linux.
os:
- linux
- osx
language: cpp
dist: trusty
addons:
apt:
sources:
- ubuntu-toolchain-r-test
- sourceline: "ppa:beineri/opt-qt-5.10.1-trusty"
packages:
- gcc-7
- g++-7
- qt510-meta-minimal
- qt510svg
- qt510imageformats
- qt510tools
before_install:
- if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
brew update ;
brew install qt5 cmake ;
brew link --force qt ;
fi
script:
- if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
export CC=gcc-7 ;
export CXX=g++-7 ;
source /opt/qt510/bin/qt510-env.sh ;
fi
- cmake --version
- qmake --version
- ...

Answer 3

Use dist: bionic. This should meet most of the cases.

Answer 4

Adding a semi-related solution after struggling with this for way too long. Hopefully, it helps someone else avoid spending the amount of time I did going through the cycle of updating travis.yml, committing, waiting for Travis...repeat til it works.
I had a C extension in a Python project that started producing failing tests in Travis, yet passed locally. Eventually, I tracked it down to the old version of gcc on the xenial environment. Here's the Travis YAML file that finally solved the issue for me:
dist: xenial
language: python
before_install:
- sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
- sudo apt-get update -q
- sudo apt-get install -y gcc-7
- export CC=/usr/bin/gcc-7
python:
- "3.6"
- "3.7"
install:
- pip install -r requirements.txt
- python setup.py build_ext --inplace
script:
- python run_tests.py
As an aside, anyone else find they want to trigger a Travis build on a specific commit to find out exactly where a problem started?