文章目录
1 什么是cdecl
cdecl是C语言声明的简称，通俗来讲就是把C语言的声明翻译成通俗语言。
2 代码
本程序暂时没有考虑错误处理，而且在处理结构、枚举和联合时只简单地用“struct”，“enum”，“union”来代表它们的具体内容。最后，这个程序假定函数的括号内没有参数列表。
# 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){
/* 推断标识符的类型 */
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){
/* 读取下一个标记到this */
char *p = this.string;
/* 略过空白字符 */
while((*p = getchar()) == ' ');
if(isalnum(*p)){
/* 读入的标识符以A-Z, 0-9开头 */
while(isalnum(*++p = getchar()));
ungetc(*p, stdin);
*p = '\0';
this.type = classify_string();
return;
}
if(*p == '*'){
strcpy(this.string, "pointer to");
this.type = '*';
return;
}
this.string[1] = '\0';
this.type = *p;
}
/* 理解所有分析过程的代码段 */
void read_to_first_identifer(){
gettoken();
while(this.type != IDENTIFIER){
push(this);
gettoken();
}
printf("%s is ", this.string); //打印标识符
gettoken();
}
void deal_with_array() {
while(this.type == '['){
printf("array ");
gettoken(); //数字或者‘]’
if(isdigit(this.string[0])){
printf("0..%d ", (atoi(this.string)-1));
gettoken(); //读取‘]’
}
gettoken(); //读取‘]’之后的再一个标记
printf("of ");
}
}
void deal_with_function_args() {
while (this.type != ')')
{
gettoken();
}
gettoken();
printf("function returning ");
}
void deal_with_pointers() {
while(stack[top].type == '*'){
printf("%s ", pop.string);
}
}
void deal_with_declarator() {
/* 处理标识符之后可能存在的数组/函数 */
switch (this.type)
{
case '[': deal_with_array();break;
case '(': deal_with_function_args();
}
deal_with_pointers();
//处理在读入到标识符之前压入到堆栈中的符号
while(top >= 0){
if(stack[top].type == '('){
pop;
gettoken(); //读取')'之后的符号
deal_with_declarator();
}else{
printf("%s ", pop.string);
}
}
}
int main() {
//将标记压入堆栈中，直到遇见标识符
printf("Please enter a C declaration: ");
read_to_first_identifer();
deal_with_declarator();
printf("\n");
return 0;
}
/*
输出示例：
Please enter a C declaration: int (*func)()
func is pointer to function returning int
Please enter a C declaration: int *(*a[3])();
a is array 0..2 of pointer to function returning pointer to int
Please enter a C declaration: struct pm i;
pm is struct
*/
3 基本思路
设计方案是弄一个堆栈，从输入流中依次向右读取，把各个标记依次压入堆栈，直到读到标识符为止。然后继续向右读入一个标记，也就是标识符右边的那个标记。接着，观察标识符左边的那个标记（需要从堆栈中弹出）。
写在最后
本文是博主阅读《C专家编程》时的摘录，为了日后方便理解复习C声明的知识，特意作此文章，同时也希望可以帮到各位，Thank you very much!
