在没有 `.get` 代码的情况下检测 pgfkeys 中的空键

Question

我正在尝试使用pgfkeys来定义一些宏的 API，但在检测某个键是否为“空”时遇到了麻烦。基于这个答案，我得到了以下代码：

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
        c/.get=\cvalA,  % this must come after #1, otherwise it won't get the values that are set
    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}}
    \def\compareval{\pgfkeysnovalue}
    \ifdefequal{\cvalA}{\compareval}{c is empty by comparison A}{c is non-empty by comparison A}

    \ifdefequal{\cvalB}{\compareval}{c is empty by comparison B}{c is non-empty by comparison B}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }
\\

    \specialsave{
        a=the values of a,
        c
    }
\\

    \specialsave{
        a=the values of a,
        c=
    }
\\

    \specialsave{
        a=the values of a,
        c={}
    }
\end{document}

生成结果：

c is empty by comparison A
c is non-empty by comparison B

c is empty by comparison A
c is non-empty by comparison B

c is non-empty by comparison A
c is non-empty by comparison B

c is non-empty by comparison A
c is non-empty by comparison B

我的问题是

1. 如何检测\cvalB、 和中的空值
2. c=我如何检测案例和中的值为c={}“空”？

Answer 1

我只添加\edef\compareval{\pgfkeysnovalue}并获得了

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
        c/.get=\cvalA,  % this must come after #1, otherwise it won't get the values that are set

    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}} 
    \def\compareval{\pgfkeysnovalue}
    \ifdefequal{\cvalA}{\compareval}{c is empty by comparison A}{c is non-empty by comparison A}
    \edef\compareval{\pgfkeysnovalue} %<-
    \ifdefequal{\cvalB}{\compareval}{c is empty by comparison B}{c is non-empty by comparison B}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }
\\

    \specialsave{
        a=the values of a,
        c
    }
\\

    \specialsave{
        a=the values of a,
        c=
    }
\\

    \specialsave{
        a=the values of a,
        c={}
    }
\end{document}

这意味着第二次比较似乎完成了您想要做的事情。

\documentclass[12pt]{article}

\usepackage{tikz}
\usepackage{etoolbox}

\newcommand{\specialsave}[1]{
    \pgfkeys{
        /specialstore/place/.cd,
        a/.initial,
        c/.initial,#1,  % there cannot be a newline before #1
    }

    \edef\cvalB{\pgfkeysvalueof{/specialstore/place/c}} 
    \edef\compareval{\pgfkeysnovalue} %<-
    \ifdefequal{\cvalB}{\compareval}{c is empty}{c is non-empty}
}
\begin{document}
    \specialsave{
        a=the values of a,
    }

    \specialsave{
        a=the values of a,
        c
    }

    \specialsave{
        a=the values of a,
        c=
    }

    \specialsave{
        a=the values of a,
        c={}
    }


    \specialsave{
        a=the values of a,
        c={pft}
    }
\end{document}