Weird C code in Bison (yyerror)

Question

I'm using Bison to create a simple parser and have some trouble understanding the C code below. To me it doesn't look like a valid statement, but gcc comepiles it neatly and the code in the block executes on parsing error.

I'd really like to know what this actually means.

The code I refer to is from http://dinosaur.compilertools.net/bison/bison_7.html#SEC66 :

yyerror (s) 
     char *s;
{
  // Some code here
}

Answer 1

That's K&R C

In modern C (C89/90 or C99) that would be:

int yyerror(char *s)
{
}

Answer 2

It means

int yyerror(char* s){
  //some code here
}

code attached to your question is just another way of specifying function argument types.

Answer 3

这是旧的K＆R C.

Answer 4

GNU bison is now at version 2.5 , see here . Why do you use such an ancient version (you refer to bison 1.25 from 1996)?

The yyerror function is for error recovery . A simple example is here