Re: implicit declaration of function 'yylex' is invalid in C99

[Paul Eggert]

On 1/17/22 02:07, Ryan Schmidt wrote:

> How can I know whether these prototypes are the right ones or if they need to 
> be different?

You look at the implementation of yylex and yyerror, and make sure the 
prototype declarations match the implementation's definition. Best 
practice is for the implementation to use the declarations, e.g. via 
'#include "y.tab.h"'.


> Does a successful compile mean the prototypes were sufficiently correct?

If you follow best practice, yes. If not, not.


> What about the static part? How would I have known that getdate.y needed the 
> prototypes to be marked static? Or is that not needed there?

'static' means the functions are not visible outside the module defining 
them. This is often useful (though not required) when the functions are 
defined by the .y file and used only there.


> What about the "int" return value of yyerror in getdate.y? Is that just a mistake and it 
> should really be "void"?

Yes, pretty much. This is explained in the Bison manual.


> conf.tab.c:1302:1: error: conflicting types for 'yyparse'
> yyparse (struct config *conf)
> ^
> conf.tab.h:116:5: note: previous declaration is here

This is because grok's #include order is messed up. conf.y includes 
conf.tab.h (which uses the type struct config) before it includes 
grok_config.h (which defines the type). C requires declaration before 
use, so it should include the files in the other order. Some compilers 
will go ahead and compile anyway, depending on their flags; others won't.


> conf.tab.c:1495:23: error: too many arguments to function call, expected 0, 
> have 2
>        yychar = yylex (&yylval, &yylloc);

This is because the yylex declaration is missing. Add 'int yylex 
(YYSTYPE *);', preferably in an include file that both conf.lex and 
conf.y include so that they both agree with the declaration (this is the 
"best practice" I mentioned above).