cdecl.txt

c的申明相当晦涩

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#define MAXTOKENS 100
#define MAXTOKENLEN 64

enum type_tag { IDENTIFIER, QUALIFIER, TYPE };

struct token {
     char type;
     char string[MAXTOKENLEN];
};
int top=-1;
struct token stack[MAXTOKENS];
struct token this;
#define pop stack[top--]
#define push(s) stack[++top]=s

enum type_tag classify_string(void)
/* figure out the identifier type */
{
    char *s = this.string;
    if (!strcmp(s,"const")) {
        strcpy(s,"read-only");
        return QUALIFIER;
    }
    if (!strcmp(s,"volatile")) return QUALIFIER;
    if (!strcmp(s,"void")) return TYPE;
    if (!strcmp(s,"char")) return TYPE;
    if (!strcmp(s,"signed")) return TYPE;
    if (!strcmp(s,"unsigned")) return TYPE;
    if (!strcmp(s,"short")) return TYPE;
    if (!strcmp(s,"int")) return TYPE;
    if (!strcmp(s,"long")) return TYPE;
    if (!strcmp(s,"float")) return TYPE;
    if (!strcmp(s,"double")) return TYPE;
    if (!strcmp(s,"struct")) return TYPE;
    if (!strcmp(s,"union")) return TYPE;
    if (!strcmp(s,"enum")) return TYPE;
    return IDENTIFIER;
}
void gettoken(void) /* read next token into "this" */
{
    char *p = this.string;
    /* read past any spaces */
    while ((*p = getchar()) == ' ' ) ;
    if (isalnum(*p)) {
        /* it starts with A-Z,0-9 read in identifier
*/
        while ( isalnum(*++p=getchar()) );
        ungetc(*p,stdin);
        *p = '\0';
        this.type=classify_string();
        return;
    }
    if (*p=='*') {
        strcpy(this.string,"指向");
        this.type = '*';
        return;
    }
    this.string[1]= '\0';
    this.type = *p;
    return;
}
/* The piece of code that understandeth all parsing.
*/
read_to_first_identifier() {
    gettoken();
    while (this.type!=IDENTIFIER) {
        push(this);
        gettoken();
    }
    printf("%s 是 ", this.string);
    gettoken();
}
deal_with_arrays() {
    while (this.type=='[') {
        printf("数组 ");
        gettoken(); /* a number or ']' */
        if (isdigit(this.string[0])) {
            printf("0..%d ",atoi(this.string)-1);
            gettoken(); /* read the ']' */
        }
        gettoken(); /* read next past the ']' */
        printf("是 ");
    }
}
deal_with_function_args() {
   while (this.type!=')') {
        gettoken();
    }
    gettoken();
    printf("函数 返回 ");
}
deal_with_pointers() {
   while ( stack[top].type== '*' ) {
        printf("%s ", pop.string );
   }
}
deal_with_declarator() {
   /* deal with possible array/function following
the identifier */
   switch (this.type) {
   case '[' : deal_with_arrays(); break;
   case '(' : deal_with_function_args();
   }
   deal_with_pointers();
    /* process tokens that we stacked while reading
to identifier */
   while (top>=0) {
       if (stack[top].type == '(' ) {
           pop;
           gettoken(); /* read past ')' */
           deal_with_declarator();
       } else {
           printf("%s ",pop.string);
       }
   }
}
main()
{
   /* put tokens on stack until we reach identifier
*/
   read_to_first_identifier();
   deal_with_declarator();
   printf("\n");
   return 0;
}