How to solve Bison warning “… has no declared type”

Question

Running Bison on this file:

%{
    #include 
    int yylex();
    void yyerror(const char*);
%}


%union
{
    char    name[100];
    int     val         


        

Answer 1

The union (%union) defined is not intended to be used directly. Rather, you need to tell Bison which member of the union is used by which expression.

This is done with the %type directive.

A fixed version of the code is:

%{
    #include 
    int yylex();
    void yyerror(const char*);
%}


%union
{
    char    name[100];
    int     val;
}

%token NUM ID
%right '='
%left '+' '-'
%left '*'

%type exp NUM
%type ID

%%

exp :   NUM     {$$ = $1;}
    | ID        {$$ = vars[$1];}
    | exp '+' exp   {$$ = $1 + $3;}
    | ID '=' exp    {$$ = vars[$1] = $3;}
;

%%