Meaning of the g++ flags "-Wall", " -W", and "-Werror"

Question

What are these and what do they do?

• -Wall
• -W
• -Werror

I am using the terminal in Ubuntu to compile programs with this command:

g++ -Wall -W -Werror main.cpp -o exec

What is the explanation?

Answer 1

• -Wall: enable a set of warning, but actually not all.
• -W: enable extra warnings. It's advised to use -Wextra instead which has the same meaning
• -Werror: every warning is treated as an error.

See GCC documentation: 3.8 Options to Request or Suppress Warnings