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libs/CLI11/book/chapters/basics.md

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+# The Basics
+
+The simplest CLI11 program looks like this:
+
+[include](../code/simplest.cpp)
+
+The first line includes the library; this explicitly uses the single file
+edition (see [Selecting an edition](/chapters/installation)).
+
+After entering the main function, you'll see that a `CLI::App` object is
+created. This is the basis for all interactions with the library. You could
+optionally provide a description for your app here.
+
+A normal CLI11 application would define some flags and options next. This is a
+simplest possible example, so we'll go on.
+
+The macro `CLI11_PARSE` just runs five simple lines. This internally runs
+`app.parse(argc, argv)`, which takes the command line info from C++ and parses
+it. If there is an error, it throws a `ParseError`; if you catch it, you can use
+`app.exit` with the error as an argument to print a nice message and produce the
+correct return code for your application.
+
+If you just use `app.parse` directly, your application will still work, but the
+stack will not be correctly unwound since you have an uncaught exception, and
+the command line output will be cluttered, especially for help.
+
+For this (and most of the examples in this book) we will assume that we have the
+`CLI11.hpp` file in the current directory and that we are creating an output
+executable `a.out` on a macOS or Linux system. The commands to compile and test
+this example would be:
+
+```term
+gitbook:examples $ g++ -std=c++11 simplest.cpp
+gitbook:examples $ ./a.out -h
+Usage: ./a.out [OPTIONS]
+
+Options:
+  -h,--help                   Print this help message and exit
+```