带参数和可选参数的环境

Question

我想创建一个接收一个参数和一个可选参数的环境，这样第一个参数将是标题，而可选参数将决定标题是左对齐还是居中。没有任何包可以实现吗？

Answer 1

可选参数可以是l或c（默认c）。

\documentclass{article}

\makeatletter
\newenvironment{something}[2][c]
 {\begin{\csname #1@somethingtitle\endcsname}
  \bfseries #2
  \end{\csname #1@somethingtitle\endcsname}}
 {\par\addvspace{\topsep}}
\newcommand\l@somethingtitle{flushleft}
\newcommand\c@somethingtitle{center}
\makeatother

\begin{document}

\begin{something}{This is centered}
This is the environment's contents
This is the environment's contents
This is the environment's contents
This is the environment's contents
\end{something}

\begin{something}[l]{This is left flush}
This is the environment's contents
This is the environment's contents
This is the environment's contents
This is the environment's contents
\end{something}

\end{document}

Answer 2

没有任何包：使用经过检查的可选参数\pdfstrcmp（pdftex 原语）。

如果#1等于left，则标题左对齐，否则居中。

\documentclass{article}

\newenvironment{foo}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  #2%
  \else
  \hfil#2\hfil%
  \fi%
  \medskip

}{}

\newcommand{\footitleformat}[1]{%
  \bfseries\MakeUppercase{#1}%
}

\newenvironment{fooother}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  \footitleformat{#2}%
  \else
  \begingroup
  \centering 
  \footitleformat{#2}%

  \endgroup
  \fi%
  \medskip

}{}



\begin{document}

\begin{foo}{This is centered}
  Foo stuff
\end{foo}


\begin{foo}[left]{This is not centered}
Other Foo stuff
\end{foo}

\begin{fooother}{This is centered again}

Yet another Foo stuff
\end{fooother}


\end{document}

\documentclass{article}

\newenvironment{foo}[2][]{%
  \ifnum\pdfstrcmp{#1}{left}=0%
  #2%
  \else
  \hfil#2\hfil%
  \fi%
  \medskip

}{}


\begin{document}

\begin{foo}{This is centered}
  Foo stuff
\end{foo}


\begin{foo}[left]{This is not centered}
Other  Foo stuff
\end{foo}


\end{document}

Answer 3

编写环境以采用键值可选参数

\documentclass{article}

\usepackage{xkeyval}

\makeatletter
% From the xkeyval documentation (section 3.3 Choice keys)
% http://texdoc.net/texmf-dist/doc/latex/xkeyval/xkeyval.pdf
\define@choicekey*{paralign}{align}[\val\nr]{left,center,right}[center]{% Add align=? key-value
  \gdef\titlealign{}%
  \ifcase\nr\relax
    \gdef\titlealign{\raggedright}\or% 0 = left
    \gdef\titlealign{\centering}\or% 1 = center
    \gdef\titlealign{\raggedleft}% 2 = right
  \fi
}
\define@cmdkey{paralign}{format}[]{}% Add format=? key-value

\newenvironment{mytitle}[2][]{%
  \par\addvspace{\medskipamount}
  \begingroup
    \setkeys{paralign}{%
      align,format,% Default settings (align=center,format={})
      #1}% Local settings
    \titlealign \cmdKV@paralign@format #2%
    \par
  \endgroup
  \nobreak\smallskip
}{%
  \par\addvspace{\medskipamount}
}
\makeatother

\begin{document}

\begin{mytitle}{Centred titled}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\begin{mytitle}[align=left]{Left-aligned title}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\begin{mytitle}[align=right,format=\bfseries]{Right-aligned title}
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus placerat 
enim ligula, a efficitur augue sodales non\ldots
\end{mytitle}

\end{document}