Function list_join

src/backend/commands/exttablecmds.c:619–645

* Join the elements of the list separated by the specified delimiter and * return as a string. There will be no whitespace added for prettyprinting, * this is more intended for serializing. The caller is responsible for * managing the returned memory. */

 * managing the returned memory.
 */
static char *
list_join(List *list, char delimiter)
{
	ListCell	   *cell;
	StringInfoData	buf;

	if (list_length(list) == 0)
		return pstrdup("");

	initStringInfo(&buf);

	foreach(cell, list)
	{
		const char *cellval;

		cellval = strVal(lfirst(cell));
		appendStringInfo(&buf, "%s%c", cellval, delimiter);
	}

	/*
	 * Rather than keeping track of when we're adding the last element, trim
	 * the final delimiter to keep it simple.
	 */
	buf.data[buf.len - 1] = '\0';

	return buf.data;
}

/*
 * Transform the FORMAT options List into a new List suitable for storing in