您好 首先，我要感谢大家的帮助 我们必须使用书中写的编译器代码 但我在定义lexan的一个函数时遇到错误 你能帮我解决吗？我把它标记为粗体
/* global.h */
#include <stdio.h> /* include declarations for i/o routines */
#include <ctype.h> /* ... and for character test routines */
#include <stdlib.h> /* ... and for some standard routines, such as exit */
#include <string.h> /* ... and for string routines */
#define BSIZE 128 /* buffer size */
#define NONE -1
#define EOS '\0'
#define NUM 256
#define DIV 257
#define MOD 258
#define ID 259
#define DONE 260
extern int tokenval = NONE; /* value of token attribute */
extern int lineno = 1;
struct entry { /* form of symbol table entry */
char *lexptr;
int token;
};
extern struct entry symtable[]; /* symbol table */
extern void init(); /* loads keywords into symtable */
extern void error(char* m); /* generates all error messages */
/*BOLD*/ extern int lexan(); /* lexical analyzer */**
extern void parse(); /* parses and translates expression list */
extern int insert(char *s, int tok); /* returns position of entry for s */
extern int lookup(char *s); /* returns position of entry for s */
extern void emit (int t, int tval); /* generates output */
/* init.c */
struct entry keywords[] = {
{ "div", DIV },
{ "mod", MOD, },
{ 0, 0 }
};
void init() /* loads keywords into symtable */
{
struct entry *p;
for (p = keywords; p->token; p++)
insert(p->lexptr, p->token);
}
/* symbol.c */
#define STRMAX 999 /* size of lexemes array */
#define SYMMAX 100 /* size of symbol table */
char lexemes[STRMAX];
int lastchar = - 1; /* last used position in lexemes */
struct entry symtable[SYMMAX];
int lastentry = 0; /* last used position in symtable */
int lookup(char *s) /* returns position of entry for s */
{
int p;
for (p = lastentry; p > 0; p = p - 1)
if (strcmp(symtable[p].lexptr, s) == 0)
return p;
return 0;
}
int insert(char *s, int tok) /* returns position of entry for s */
{
int len;
len = strlen(s); /* strlen computes length of s */
if (lastentry + 1 >= SYMMAX)
error ("symbol table full");
if (lastchar + len + 1 >= STRMAX)
error ("lexemes array full");
lastentry = lastentry + 1;
symtable[lastentry].token = tok;
symtable[lastentry].lexptr = &lexemes[lastchar + 1];
lastchar = lastchar + len + 1;
strcpy(symtable[lastentry].lexptr, s);
return lastentry;
}
/* lexer.c */
char lexbuf[BSIZE];
int lexan () /* lexical analyzer */
{
int t;
while(1) {
t = getchar ();
if (t == ' ' || t == '\t')
; /* strip out white space */
else if (t == '\n')
lineno = lineno + 1;
else if (isdigit (t)) { /* t is a digit */
ungetc(t, stdin);
scanf("%d", &tokenval);
return NUM;
}
else if (isalpha(t)) { /* t is a letter */
int p, b = 0;
while (isalnum(t)) { /* t is alphanumeric */
lexbuf [b] = t;
t = getchar ();
b = b + 1;
if (b >= BSIZE)
error("compiler error");
}
lexbuf[b] = EOS;
if (t != EOF)
ungetc(t, stdin);
p = lookup (lexbuf);
if (p == 0)
p = insert (lexbuf, ID);
tokenval = p;
return symtable[p].token;
}
else if (t == EOF)
return DONE;
else {
tokenval = NONE;
return t;
}
}
}
/* emitter.c */
void emit (int t, int tval) /* generates output */
{
switch(t) {
case '+' : case '-' : case '*' : case '/':
printf("%c\n", t); break;
case DIV:
printf("DIV\n"); break;
case MOD:
printf("MOD\n"); break;
case NUM:
printf("%d\n", tval); break;
case ID:
printf("%s\n", symtable[tval].lexptr); break;
default:
printf("token %d, tokenval %d\n", t, tval);
}
}
/* parser.c -- without the optimizations */
int lookahead;
void match(int);
void start(), list(), expr(), moreterms(), term(), morefactors(), factor();
void parse() /* parses and translates expression list */
{
lookahead = lexan();
start();
}
void start ()
{
/* Just one production for start, so we don't need to check lookahead */
list(); match(DONE);
}
void list()
{
if (lookahead == '(' || lookahead == ID || lookahead == NUM) {
expr(); match(';'); list();
}
else {
/* Empty */
}
}
void expr ()
{
/* Just one production for expr, so we don't need to check lookahead */
term(); moreterms();
}
void moreterms()
{
if (lookahead == '+') {
match('+'); term(); emit('+', tokenval); moreterms();
}
else if (lookahead == '-') {
match('-'); term(); emit('-', tokenval); moreterms();
}
else {
/* Empty */
}
}
void term ()
{
/* Just one production for term, so we don't need to check lookahead */
factor(); morefactors();
}
void morefactors ()
{
if (lookahead == '*') {
match('*'); factor(); emit('*', tokenval); morefactors();
}
else if (lookahead == '/') {
match('/'); factor(); emit('/', tokenval); morefactors();
}
else if (lookahead == DIV) {
match(DIV); factor(); emit(DIV, tokenval); morefactors();
}
else if (lookahead == MOD) {
match(MOD); factor(); emit(MOD, tokenval); morefactors();
}
else {
/* Empty */
}
}
void factor ()
{
if (lookahead == '(') {
match('('); expr(); match(')');
}
else if (lookahead == ID) {
int id_lexeme = tokenval;
match(ID);
emit(ID, id_lexeme);
}
else if (lookahead == NUM) {
int num_value = tokenval;
match(NUM);
emit(NUM, num_value);
}
else
error("syntax error in factor");
}
void match(int t)
{
if (lookahead == t)
lookahead = lexan();
else
error ("syntax error in match");
}
/* error.c */
void error(char* m) /* generates all error messages */
{
fprintf(stderr, "line %d: %s\n", lineno, m);
exit(EXIT_FAILURE); /* unsuccessful termination */
}
/* main.c */
int main(void)
{
init();
parse();
exit(0); /* successful termination */
}
/*BOLD*/ int lexan() /* lexical analyzer */
{
int t;
while(1) {
t = getchar ();
if (t == ' ' || t == '\t')
; /* strip out white space */
else if (t == '\n')
lineno = lineno + 1;
else if (isdigit (t)) { /* t is a digit */
ungetc(t, stdin);
scanf("%d", &tokenval);
return NUM;
}
else if (isalpha(t)) { /* t is a letter */
int p, b = 0;
while (isalnum(t)) { /* t is alphanumeric */
lexbuf [b] = t;
t = getchar ();
b = b + 1;
if (b >= BSIZE)
error("compiler error");
}
lexbuf[b] = EOS;
if (t != EOF)
ungetc(t, stdin);
p = lookup (lexbuf);
if (p == 0)
p = insert (lexbuf, ID);
tokenval = p;
return symtable[p].token;
}
else if (t == EOF)
return DONE;
else {
tokenval = NONE;
return t;
}
}
}
答案 0 :(得分：2)
我得到了一大堆编译器错误：
$ cc -c a.c
a.c:18: warning: ‘tokenval’ initialized and declared ‘extern’
a.c:19: warning: ‘lineno’ initialized and declared ‘extern’
a.c:31: error: expected identifier or ‘(’ before ‘extern’
a.c:267: error: redefinition of ‘lexan’
a.c:90: note: previous definition of ‘lexan’ was here
如果你读过行号，你可以自己解决这些问题。
一个接一个：
extern int tokenval = NONE;
extern int lineno = 1;
分配extern声明。这是不允许的。删除extern。事实上，您不需要任何extern修饰符，因为所有代码都在当前模块中。
int lexan(); /* lexical analyzer */**
// the error is here ^^
最后一个错误是lexan定义了两次。