“-Wall"是什么意思?在“g++ -Wall test.cpp -o test"中做?

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

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

解决方案

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.