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

From: Akim Demaille
Subject: Re: implicit declaration of function 'yylex' is invalid in C99
Date: Sat, 15 Jan 2022 17:02:07 +0100


> Le 15 janv. 2022 à 11:04, Ryan Schmidt <bison@ryandesign.com> a écrit :
> On Jan 15, 2022, at 03:57, Akim Demaille wrote:
>> I personally feel that generating these prototypes automatically is actually 
>> more complex (for the user, not for Bison) than merely specifying them.
> Ok. Can you provide any guidance for how to specify them?
> I am a maintainer of packages within the MacPorts package management system.

And I thank you a lot for the effort you put into the MacPorts.

> I've encountered many of our ports that fail to build for this reason, and I 
> haven't known how to fix them. For other implicit declaration of function 
> problems it's usually been a simple matter of including a missing header or 
> writing a function prototype, but with bison/flex, there isn't a .c or .h 
> file into which such a prototype could be inserted, and even if I knew what 
> file to insert it into, I wouldn't know what prototype to write.

It very much depends on the *.l and the *.y files.  But most of the time it 
suffices to include something like

%code provides {
  int yylex (void);
  void yyerror (const char *);

in the first part of the *.y file (before %%).

If you provide me with pointers to these packages, I can help finding the 
appropriate fixes.

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