Tutorial by Topics: arguments



Variable arguments are used by functions in the printf family (printf, fprintf, etc) and others to allow a function to be called with a different number of arguments each time, hence the name varargs.

To implement functions using the variable arguments feature, use #include <stdarg.h>.

To call functions which take a variable number of arguments, ensure there is a full prototype with the trailing ellipsis in scope: void err_exit(const char *format, ...); for example.

Most command line tools rely on arguments passed to the program upon its execution. Instead of prompting for input, these programs expect data or specific flags (which become booleans) to be set. This allows both the user and other programs to run the Python file passing it data as it starts. This section explains and demonstrates the implementation and usage of command line arguments in Python.

Varargs, as they are commonly known, allow functions to take an arbitrary number of arguments without specification. All arguments given to such a function are packaged into a single structure known as the vararg list; which is written as ... in Lua. There are basic methods for extracting the number of given arguments and the value of those arguments using the select() function, but more advanced usage patterns can leverage the structure to it's full utility.

Rust's standard library does not contain a proper argument parser (unlike argparse in Python), instead preferring to leave this to third-party crates. These examples will show the usage of both the standard library (to form a crude argument handler) and the clap library which can parse command-line arguments more effectively.

The ByRef and ByVal modifiers are part of a procedure's signature and indicate how an argument is passed to a procedure. In VBA a parameter is passed ByRef unless specified otherwise (i.e. ByRef is implicit if absent).

Note In many other programming languages (including VB.NET), parameters are implicitly passed by value if no modifier is specified: consider specifying ByRef modifiers explicitly to avoid possible confusion.


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