如何在 Latex 中比较两个字符

Question

我需要比较两个字符（或字符串），但我不能：

请问你能帮帮我吗！！

\documentclass[a4paper,openright,twoside]{book}
\usepackage{xstring,ifthen}

\begin{document}
\def\cero{\StrMid{01}{1}{1}}
\def\uno{\StrMid{01}{2}{2}}

\def\word{101010101}
\def\bit{\StrMid{\word}{5}{5}}


this is cero: \cero \\
this is one: \uno


this is the word: \word \\
this is the 5th bit: \bit

.... but I cant't compare them!!

\ifthenelse{\equal{\bit}{\uno}}
    {this is 1}
    {this is 0}
\end{document}

Answer 1

使用\def\bit{\StrMid{\word}{5}{5}}，宏\bit是不是0 或 1，但它是印刷0 或 1。

您应该使用可选参数\StrMid（几个函数共用xstrings）：

\documentclass[a4paper,openright,twoside]{book}
\usepackage{xstring,ifthen}

\begin{document}
\StrMid{01}{1}{1}[\cero]
\StrMid{01}{2}{2}[\uno]

\def\word{101010101}
\StrMid{\word}{5}{5}[\bit]

this is cero: \cero

this is one: \uno

this is the word: \word

this is the 5th bit: \bit

\ifthenelse{\equal{\bit}{\uno}}
    {this is 1}
    {this is 0}

\end{document}

Answer 2

expl3使用字符串范围函数的解决方案

\documentclass{book}
\usepackage{expl3}
\usepackage{ifthen}
\ExplSyntaxOn
\cs_new_eq:NN \midstr \str_range:nnn
\cs_new_eq:NN \Midstr \str_range:Nnn
\ExplSyntaxOff
\begin{document}
\def\cero{\midstr{01}{1}{1}}
\def\uno{\midstr{01}{2}{2}}

\def\word{101010101}
\def\bit{\Midstr{\word}{5}{5}}


this is cero: \cero \\
this is one: \uno


this is the word: \word \\
this is the 5th bit: \bit

.... but I cant't compare them!!

\ifthenelse{\equal{\bit}{\uno}}
    {this is 1}
    {this is 0}

\end{document}

请注意，这使用了“真实”的 TeX 字符串（IE\midstr/的结果\Mistr 仅为类别代码 12 的标记，空格除外，其类别代码为 10）。