Insert a special integral sign

Question

I'm trying to insert an integral sign that has a "C" imposed on. Specifically, I need the unicode character U+2A10, which looks like: ⨐ .

I do not want to use the stix package or XeLaTex.

Thanks!

Answer 1

Here's a sans serif c superimposed to the integral symbol:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\circint}{\mathop{\mathpalette\docircint\relax}\!\int}
\newcommand{\docircint}[2]{%
  \ifx#1\displaystyle
    \displaycircint
  \else
    \normalcircint{#1}%
  \fi
}
\newcommand{\displaycircint}{\displaystyle\mathsf{c}\mkern-18mu}
\newcommand{\normalcircint}[1]{%
  \smallerc{#1}\ifx#1\textstyle\mkern-9mu\else\mkern-8.2mu\fi
}
\newcommand{\smallerc}[1]{%
  \vcenter{\hbox{$\ifx#1\textstyle\scriptstyle\else\scriptscriptstyle\fi\mathsf{c}$}}%
}

\begin{document}

$\displaystyle A+\int_a^b+\int\limits_{X}$

$\displaystyle A+\circint_a^b+\circint\limits_{X}$

$A+\circint_a^b+\circint_X$

$\scriptstyle A+\circint_a^b+\circint_X$

\end{document}

Answer 2

Here is a simpler alternative:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\DeclareMathOperator{\circint}{
\mathchoice%
    {\ooalign{$\displaystyle\int$\cr\large$\mkern4mu\mathcal{C}$\cr $\displaystyle\int$}}
    {\ooalign{$\int$\cr\scriptsize$\mkern3mu\mathcal{C}$\cr $\int$}}
    {\ooalign{$\scriptstyle\int$\cr\tiny$\mkern2mu\mathcal{C}$\cr $\scriptstyle\int$}}
    {\ooalign{$\scriptscriptstyle\int$\cr\tiny$\mathcal{C}$\cr $\scriptscriptstyle\int$}}
}
\makeatother

\begin{document}
\(_{_{\circint_{-\infty}^{\infty} f(x)\,dx+\int_{-\infty}^{\infty} f(x)\,dx}}\)

\(_{\circint_{-\infty}^{\infty} f(x)\,dx+\int_{-\infty}^{\infty} f(x)\,dx}\)

\(\circint_{-\infty}^{\infty} f(x)\,dx+\int_{-\infty}^{\infty} f(x)\,dx\)

\(\displaystyle\circint_{-\infty}^{\infty} f(x)\,dx+\int_{-\infty}^{\infty} f(x)\,dx\)
\end{document}