According to Yashu's instructions, I wrote the following function (it's PL/SQL code, but it should be easily adaptable to any other language).
FUNCTION field(str IN VARCHAR2) RETURN VARCHAR2 IS
C_NEWLINE CONSTANT CHAR(1) := '
'; -- newline is intentional
v_aux VARCHAR2(32000);
v_has_double_quotes BOOLEAN;
v_has_comma BOOLEAN;
v_has_newline BOOLEAN;
BEGIN
v_has_double_quotes := instr(str, '"') > 0;
v_has_comma := instr(str,',') > 0;
v_has_newline := instr(str, C_NEWLINE) > 0;
IF v_has_double_quotes OR v_has_comma OR v_has_newline THEN
IF v_has_double_quotes THEN
v_aux := replace(str,'"','""');
ELSE
v_aux := str;
END IF;
return '"'||v_aux||'"';
ELSE
return str;
END IF;
END;