我用flex编写的词法分析器有问题。当我试图编译它时,没有创建任何exe文件,我得到了很多错误。以下是flex文件:
%{
#ifdef PRINT
#define TOKEN(t) printf("Token: " #t "n");
#else
#define TOKEN(t) return(t);
#endif
%}
delim [ tn]
ws {delim}+
digit [0-9]
id {character}({character}|{digit})*
number {digit}+
character [A-Za-z]
%%
{ws} ; /* Do Nothing */
":" TOKEN(COLON);
";" TOKEN(SEMICOLON);
"," TOKEN(COMMA);
"(" TOKEN(BRA);
")" TOKEN(CKET);
"." TOKEN(DOT);
"'" TOKEN(APOS);
"=" TOKEN(EQUALS);
"<" TOKEN(LESSTHAN);
">" TOKEN(GREATERTHAN);
"+" TOKEN(PLUS);
"-" TOKEN(SUBTRACT);
"*" TOKEN(MULTIPLY);
"/" TOKEN(DIVIDE);
{id} TOKEN(ID);
{number} TOKEN(NUMBER);
'{character}' TOKEN(CHARACTER_CONSTANT);
%%
这些是我收到的错误:
spl.l: In function 'yylex':
spl.l:19:7: error: 'COLON' undeclared (first use in this function)
":" TOKEN(COLON);
^
spl.l:5:25: note: in definition of macro 'TOKEN'
#define TOKEN(t) return(t);
^
spl.l:19:7: note: each undeclared identifier is reported only once for each function it appears in
":" TOKEN(COLON);
^
spl.l:5:25: note: in definition of macro 'TOKEN'
#define TOKEN(t) return(t);
^
spl.l:20:7: error: 'SEMICOLON' undeclared (first use in this function)
";" TOKEN(SEMICOLON);
^
spl.l:5:25: note: in definition of macro 'TOKEN'
#define TOKEN(t) return(t);
我用来编译的命令是:
flex a.l
gcc -o newlex.exe lex.yy.c -lfl
有人能看出我哪里出了问题吗?
您必须首先定义令牌。COLON
、SEMICOLON
等pp的定义(即id)不是由flex生成的。您可以在lexer文件顶部的枚举中定义它:
%{
#ifdef PRINT
#define TOKEN(t) printf("Token: " #t "n");
#else
#define TOKEN(t) return(t);
#endif
enum { COLON = 257, SEMICOLON, COMMA, BRA, CKET, DOT, APOS, EQUALS,
LESSTHAN, GREATERTHAN, PLUS, SUBTRACT, MULTIPLY, DIVIDE,
ID, NUMBER, CHARACTER_CONSTANT };
%}
我建议ids>257也可以直接从lexer返回ascii字符代码进行进一步处理。然而,通常在yacc/bison的解析器文件中也会使用令牌名称,该解析器文件会生成一个头文件(默认名称为y.tab.h
)以包含在lexer中,该头文件包含为那些与解析器函数匹配的令牌生成的id。