LaTeX中\newcommand, \renewcommand, \providecommand的用法

LaTeX中\newcommand, \renewcommand, \providecommand的用法

\newcommand defines a new command, and makes an error if it is already defined.

\renewcommand redefines a predefined command, and makes an error if it is not yet defined.

\providecommand defines a new command if it isn't already defined,  or does nothing if it exists.

If you want to define a command whether it is new or predefined, you can use \def or

• \providecommand \foo{}
• \renewcommand \foo{…}