It also shall contain a copy of the #define statements in the header file.

It also shall contain prototype declarations of the yyerror() and yylex() functions, and a copy of the #define statements in the header file, prior to any code copied from within <tt>%{</tt> and <tt>%}</tt> in the declarations section in grammar.

The code file shall not contain a declaration of the main() function, unless one is present within <tt>%{</tt> and <tt>%}</tt> in the declarations section in grammar.

Earlier versions of this standard did not require the code file created by yacc to contain declarations of yyerror() and yylex(). This meant that portable applications that did not define them had to declare them in the grammar file, to ensure they would not be diagnosed by the compiler as being called without being declared, but this was not stated in those versions of the standard either. The standard developers decided it was preferable for yacc to include the declarations in the code file and this is now a requirement.

Earlier versions of this standard were also silent about a declaration of main(). However, the equivalent solution was not adopted since a declaration of main() would only be needed if it is called recursively by an application. Although in theory an application could call the yacc library version of main() from code in a grammar file, it is questionable why any application (other than a test suite) would do so, in particular because that version of main() does not accept any arguments and it calls exit() -- it does not return -- and therefore is of little use recursively. An application that includes its own definition of main() could call it recursively, but can reasonably be expected to ensure it does not call main() without previously defining or declaring it. An additional complication is that main() has multiple different allowed prototypes. The standard developers decided the simplest solution was not to allow yacc to provide a declaration of main() in the code file.