LaTeX Symbol - Integral with a circle (integral over a closed line)

The \oint outputs an integral over a closed line.

\oint f(x)dx \\~\\
\oint f(x) dx \\~\\
\oint f(x) \ dx \\~\\
\oint f(x) \, dx

\[ \oint f(x)dx \\~\\ \oint f(x) dx \\~\\ \oint f(x) \ dx \\~\\ \oint f(x) \, dx \]

It depends on the LaTeX editor or environment, but above examples show f(x) is very close to dx in default so there needs a bit space like \,.

\oint_C f(x) \, dx

\[ \oint_C f(x) \, dx \]