Yacc 范围问题
所以我四处寻找这个问题的答案，但我唯一能收集到的是我遇到了范围问题。
错误读取 ch3-05.y:54: error: Expected '=', ',', ';', 'asm' or 'attribute' before '{' token
这是我的代码逐字
%{
#include <stdio.h>
#include "ch3hdr2.h"
#include <string.h>
#include <math.h>
%}
%union {
double dval;
struct symtab *symp;
}
%token <symp> NAME
%token <dval> NUMBER
%left '-' '+'
%left '*' '/'
%nonassoc UMINUS
%type <dval> expression
%%
statement_list : statement '\n'
| statement_list statement '\n'
;
statement : NAME '=' expression {$1->value = $3;}
| expression { printf("= %g \n", $1); }
expression : expression '+' expression { $$ = $1 + $3;}
| expression '-' expression { $$ = $1 - $3;}
| expression '*' expression { $$ = $1 * $3;}
| expression '/' expression {
if($3 == 0.0)
yyerror("divide by zero");
else
$$ = $1 / $3;
}
| '_' expression %prec UMINUS {$$ = -$2;}
| '(' expression ')' { $$ = $2;}
| NUMBER
| NAME {$$ = $1->value; }
| NAME '(' expression ')' {
if($1 ->funcptr)
$$ = ($1->funcptr) ($3);
else {
printf("%s not a function\n", $1->name);
$$ = 0.0;
}
}
;
%%
struct symtab *
symlook(s)
char *s;
{ // this is where the error is
char *p;
struct symtab *sp;
for(sp = symtab; sp < &symtab[NSYMS]; sp++){
if(sp -> name && !strcmp(sp->name, s))
return sp;
if(!sp->name) {
sp->name = strdup(s);
return sp;
}
}
yyerror("TOO MANY SYMBOLS");
exit(1);
}
addfunc(name, func)
char *name;
double (*func)();
{
struct sumtab *sp = symlook(name);
sp->funcptr = func;
}
main()
{
extern double sqrt(), exp(), log();
addfunc("sqrt", sqrt);
addfunc("exp", exp);
addfunc("log", log);
yyparse();
}
我一直盯着屏幕，但还没有任何效果。任何帮助将不胜感激。
另外，后来我又遇到了一些错误，但我认为这可能是因为我还没有解决这个问题。
这是我对 ch3hdr2.h 的内容
#define NSYMS 20 /* max number of symbols */
struct symtab {
char *name;
double (*funcptr)();
double value;
} symtab [NSYMS];
struct symtab *symlook();
So I looked around for an answer to this, but the only thing I could gather was that i was having a scope problem.
The error reads ch3-05.y:54: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘attribute’ before ‘{’ token
Here is my code verbatim
%{
#include <stdio.h>
#include "ch3hdr2.h"
#include <string.h>
#include <math.h>
%}
%union {
double dval;
struct symtab *symp;
}
%token <symp> NAME
%token <dval> NUMBER
%left '-' '+'
%left '*' '/'
%nonassoc UMINUS
%type <dval> expression
%%
statement_list : statement '\n'
| statement_list statement '\n'
;
statement : NAME '=' expression {$1->value = $3;}
| expression { printf("= %g \n", $1); }
expression : expression '+' expression { $ = $1 + $3;}
| expression '-' expression { $ = $1 - $3;}
| expression '*' expression { $ = $1 * $3;}
| expression '/' expression {
if($3 == 0.0)
yyerror("divide by zero");
else
$ = $1 / $3;
}
| '_' expression %prec UMINUS {$ = -$2;}
| '(' expression ')' { $ = $2;}
| NUMBER
| NAME {$ = $1->value; }
| NAME '(' expression ')' {
if($1 ->funcptr)
$ = ($1->funcptr) ($3);
else {
printf("%s not a function\n", $1->name);
$ = 0.0;
}
}
;
%%
struct symtab *
symlook(s)
char *s;
{ // this is where the error is
char *p;
struct symtab *sp;
for(sp = symtab; sp < &symtab[NSYMS]; sp++){
if(sp -> name && !strcmp(sp->name, s))
return sp;
if(!sp->name) {
sp->name = strdup(s);
return sp;
}
}
yyerror("TOO MANY SYMBOLS");
exit(1);
}
addfunc(name, func)
char *name;
double (*func)();
{
struct sumtab *sp = symlook(name);
sp->funcptr = func;
}
main()
{
extern double sqrt(), exp(), log();
addfunc("sqrt", sqrt);
addfunc("exp", exp);
addfunc("log", log);
yyparse();
}
I've been staring at the screen but nothing as worked yet. Any help will be greatly appreciated.
Also, I get a few more errors later on, but I think it may be because I haven't resolved this one yet.
Here is what I have for ch3hdr2.h
#define NSYMS 20 /* max number of symbols */
struct symtab {
char *name;
double (*funcptr)();
double value;
} symtab [NSYMS];
struct symtab *symlook();
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评论（3）
您在
addfunc()中的拼写错误是struct sumtab而不是struct symtab。否则，代码在 GCC（MacOS X 10.6.7 上的 4.6.0）下编译时会出现一些轻微的问题。
您可能会遇到类似于使用 G++ 而不是 GCC 进行编译时遇到的错误：
这是因为函数样式在 C++ 中无效，即使它在 C 中“OK”（但过时）。
您实际使用的是哪个编译器 -在哪个平台上？
修复拼写错误后，当我将
#include添加到标头列表并使用 GCC 4.2.1 (XCode 3) 或 GCC 4.6.0 时，代码将编译为警告，但它编译：GCC 4.6.0 输出很有趣 - 更容易看到触发每个警告的内容：
You have a typo
struct sumtabinstead ofstruct symtabat inaddfunc().Otherwise, the code compiles under GCC (4.6.0 on MacOS X 10.6.7) with some minor wittering.
You can get an error similar to the one you get if you compile with G++ instead of GCC:
That's because the function style is invalid in C++ even though it is 'OK' (but archaic) in C.
Which compiler are you actually using - on which platform?
After fixing the typo, when I add
#include <stdlib.h>to the list of headers and use either GCC 4.2.1 (XCode 3) or GCC 4.6.0, then the code compiles with warnings, but it compiles:The GCC 4.6.0 output is interesting - much easier to see what triggers each warning:
不要看 yacc 代码。打开生成的
y.tab.c文件（或任何您命名的文件）并查看 C 代码。这将更好地指示问题所在，因为正是编译器正在尝试处理的问题。有时，yacc 放入 C 代码中的
#file和#line构造只会造成妨碍。我的第一个想法是它与古老的函数“原型”有关。您可能需要考虑重新执行这些操作，例如：
如果做不到这一点，我经常会看到类似于返回类型的定义不存在的错误。确保此时已经完全定义了 struct symtab 。
然后，如果还是不行，把生成的C源代码（包括头文件）以及yacc代码贴出来。
Don't look at the yacc code. Open up the generated
y.tab.cfile (or whatever you've called it) and look at the C code.That will be a better indicator of what the problem is since that is what the compiler is trying to process. Sometimes the
#fileand#lineconstructs that yacc puts into the C code just get in the way.My first thoughts are that it has something to do with the archaic function "prototypes". You may want to consider re-doing these like:
Failing that, I often see errors similar to that where the definition of a return type is not in existence. Make sure that
struct symtabhas been fully defined at that point.Then, if it still doesn't work, post the generated C source code (including header files) as well as the yacc code.
我怀疑问题可能是 addfunc 中的 struct sumtab 。否则，ch3hdr2.h 头文件或它包含的其他一些头文件可能有问题......
I suspect the problem is probably the
struct sumtabin addfunc. Otherwise, its likely something wrong in the ch3hdr2.h header file or some other header file it includes...