Numeric-style citation call-outs encased in round parentheses instead of square brackets, with custom makebst-made bibliography style

Question

I have made a custom bibliography style with the makebst utility, where i chose numerical in-text citations. The default style is apparently with square brackets around the citation number, but i need parentheses around the number.

My style is not compatible with the natbib package so the "change square to round" solution does not solve the problem.

Here is my custom.bst which i made to suit the needs of the American Journal of Clinical Nutrition.

MWE:

\documentclass[12pt,letterpaper]{article}
\usepackage[margin=2.54cm]{geometry}

\makeatletter
\renewcommand{\@biblabel}[1]{\quad#1.}
\makeatother

  \begin{document}
    I want these square brackets to be parentheses\cite{Turner-McGrievy2015}, like this(1).

    \bibliographystyle{ajcn}
    \bibliography{library}
  \end{document}

Answer 1

My [makebst-produced bibliography] style is not compatible with the natbib package

You should check the correctness of this claim. The custom-bib package and its makebst utility were written by the person who also authored the natbib citation management package. As such, bespoke bibliography styles created with the makebst should generally be eminently compatible with natbib.

You should load the natbib package with the options round and numbers. Be sure to recompile twice in order to propagate all changes.

\RequirePackage{filecontents}
\begin{filecontents}{library.bib} % create a dummy entry
@misc{Turner-McGrievy2015, author = "A", title = "B", year = 2015}
\end{filecontents}

\documentclass[12pt,letterpaper]{article}
\usepackage[margin=1in]{geometry}
\usepackage[round,numbers]{natbib}
\bibliographystyle{ajcn}  
\makeatletter
\renewcommand{\@biblabel}[1]{\quad#1.}
\makeatother

\begin{document}
I want the fences around a citation call-out, e.g., 
\cite{Turner-McGrievy2015}, to be like ``(1)''.

\bibliography{library}
\end{document}