What does “-Wall” in “g++ -Wall test.cpp -o test” do?

Question

-o changes the output filename (I found that using --help)

But I can\'t find out what -Wall does?

Answer 1

It's short for "warn all" -- it turns on (almost) all the warnings that g++ can tell you about. Typically a good idea, especially if you're a beginner, because understanding and fixing those warnings can help you fix lots of different kinds of problems in your code.