C5 - 5.12 Complicated Declarations

 

 

5.12 Complicated Declarations

The C Programming Language

 

超级经典又有诠释力的例子：dcl.c

 

重点要掌握的是 dcl()和 dirdcl() 的交互，然后是gettoken()

 

#include <stdio.h>
#include <string.h>
#include <ctype.h>

#define MAXTOKEN 100

enum { NAME, PARENS, BRACKETS };

void dcl(void);
void dirdcl(void);

int gettoken(void);
int tokentype;
char token[MAXTOKEN];
char name[MAXTOKEN];
char datatype[MAXTOKEN];
char out[1000];

int main()
{
  while (gettoken() != EOF) {
    strcpy(datatype, token);
    out[0] = '\0';
    dcl();
    if(tokentype != '\n')
      printf("syntax error\n");
    printf("%s: %s %s\n", name, out, datatype);
  }
  return 0;
}

int gettoken(void)
{
  int c;
  char *p = token;
  
  while ((c = getchar()) == ' ' || c == '\t')
    ;
  if(c == '(') {
    if((c = getchar()) == ')') {
      strcpy(token, "()");
      return tokentype = PARENS;
    } else {
      ungetc(c, stdin);
      return tokentype = '(';
    }
  } else if (c == '[') {
    for(*p++ = c; (*p++ = getchar()) != ']'; )
      ;
    *p = '\0';
    return tokentype = BRACKETS;
  } else if (isalpha(c)) {
    for(*p++ = c; isalnum(c = getchar()); )
      *p++ = c;
    *p = '\0';
    ungetc(c, stdin);
    return tokentype = NAME;
  } else {
    return tokentype = c;
  }
}

void dcl(void){
  int ns;
  for(ns = 0; gettoken() == '*'; )
    ns++;
  dirdcl();
  while(ns-- > 0)
    strcat(out, " pointer to");
}

void dirdcl(void){
  int type;
  if(tokentype == '('){
    dcl();
    if(tokentype != ')')
      printf("error: missing )\n");
  }else if(tokentype == NAME)
    strcpy(name, token);
  else
    printf("error: expected name of (dcl)\n");
  while((type = gettoken()) == PARENS || type == BRACKETS)
    if(type == PARENS)
      strcat(out, " function returning");
    else {
      strcat(out, " array");
      strcat(out, token);
      strcat(out, " of");
    }
}