一个C语言声明解析器的设计与实现
概论：C语言的声明解析往往复杂多样，使得初学者不知所云，例如double (*(*(*fp3)())[10])() 定义的是什么？int ＊a［10］和int （＊a）［10］有什么区别？C语言的声明解析遵循什么规则？本文主要为你介绍C语言声明解析的规则，然后为你介绍编译器的一个与之相关的部分——声明解析器的设计与实现。
本文来源：一个C语言声明解析器的设计与实现
关于C语言的声明解析规则，可以参考这里：
char string［MAXTOKENLEN］；｝；
read_to_first_identifier（）:
读到第一个标识符号
gettoken()
入栈，直到遇到第一个标识符
deal with declaration()//递归
具体的代码：
#include<stdio.h>#include<ctype.h>#include<unistd.h>#include<stdlib.h>#include<string.h>#define MAXTOKENLEN 64#define MAXTOKENS 100#define MAXDECLLEN 200struct token{ char type; char string[MAXTOKENLEN];};struct decl{ char string[MAXDECLLEN]; int current_location;};struct decl mydecl;int top=-1;struct token this;//the current tokenstruct token stack[MAXTOKENS];//the tokens before the first identifer#define IDENTIFIER 'I'#define QUALIFIER 'Q'#define TYPE 'T'#define pop stack[top--]#define push(s) stack[++top]=s//#define debug char classify_string(const char *string);int main(int argc, char *argv[]){ init_parse_decl(); read_to_first_identifier(); deal_with_declaration(); printf("\n"); return 0;}/* * init the value of mydecl*/int init_parse_decl(){ if( fgets(mydecl.string,MAXDECLLEN,stdin) == NULL){ perror("can not read from the stdin"); } if(strlen(mydecl.string)==MAXDECLLEN-1) printf("you input is too long, you may get an error!"); mydecl.current_location=0; #ifdef debug printf("init:we get last char of mydecl:%c,%d\n",mydecl.string[strlen(mydecl.string)],mydecl.string[strlen(mydecl.string)]); #endif}/* get a token from the current string,value the "this" and move the pointernotice: we may get a '\0' at the end of the string */int gettoken(){ char *ch_pointer=this.string; //leave out the blank while(mydecl.string[mydecl.current_location]==' '){ mydecl.current_location++; } *ch_pointer=mydecl.string[mydecl.current_location]; if(isalnum(*ch_pointer)){ while(isalnum(*ch_pointer)){ mydecl.current_location++; ch_pointer++; *ch_pointer=mydecl.string[mydecl.current_location];}*ch_pointer='\0';this.type=classify_string(this.string );//indentifier,qualifier,type#ifdef debug printf("we get token:%s ",this.string );#endifreturn 1; } //else:(, ), [, ] // printf("current location is:%d\n",mydecl.current_location); // printf("(%d)",mydecl.string[mydecl.current_location]); switch(*ch_pointer){ case '*': case '(': case ')': case '[': case ']': this.type=*ch_pointer; this.string[1]='\0'; mydecl.current_location++; #ifdef debug printf("we get token:%s ",this.string ); #endif break; case '\n': case '\0':this.type='\0'; // printf("we come to the end\n"); strcpy(this.string,"then end"); return 0; default : printf("we can not read this indentifier %d\n",*ch_pointer); parse_error(); } return 1;}char classify_string(const char *string){ if(isspace(*string)) return '\0'; if(!strcmp(string,"const")) return QUALIFIER; if(!strcmp(string,"volatile")) return QUALIFIER; if(!strcmp(string,"void")) return TYPE; if(!strcmp(string,"char")) return TYPE; if(!strcmp(string,"signed")) return TYPE; if(!strcmp(string,"unsigned")) return TYPE; if(!strcmp(string,"short")) return TYPE; if(!strcmp(string,"int")) return TYPE; if(!strcmp(string,"long")) return TYPE; if(!strcmp(string,"float")) return TYPE; if(!strcmp(string,"struct")) return TYPE; if(!strcmp(string,"union")) return TYPE; if(!strcmp(string,"enum")) return TYPE; return IDENTIFIER ;}/*follow the dec string until the first identifier,push token to a stack*/int read_to_first_identifier(const char *mydecl){ if(gettoken()==0){ printf("readtofirst:missing the identifier,please put in your string...\n"); return 0; } //the token is a struct with member type and string while(this.type!=IDENTIFIER) { push(this);//a stack with element of token if(gettoken()==0){ printf("readtofirst:missing the identifier\n"); return 0; } } printf("%s is ", this.string); return 1;}/*deal with the next token in diff ways according to the token typewe just go to right1) "(":deal in a function way,deal_with_declaration,2) "[":deal in a array way,deal_with_declaration,3) ")":deal with a pointer way,deal_with_declaration4) NULL:move_left,*/int deal_with_declaration(){ if(gettoken()==0){ move_left(); return 1; } // switch(this.type){ case '(': deal_with_function();break; case ')': deal_with_pointer();break; case '[': deal_with_array();break; default : printf("there should not be a %c after the identifier\n",this.type );parse_error(); } deal_with_declaration();}/*the current token is [,the content in the '[]' may be digtal,al,and other*/int deal_with_array(){ printf("array of "); while(this.type!=']'){ gettoken();//we may get an "]" or digital if(isdigit(this.string[0])){ printf("%d ", atoi(this.string)); //the next token must be ] gettoken(); if(this.type!=']'){printf("the array miss the ']'before %s",this.string);parse_error(); } } } return 0;}int parse_error(){printf("press any key to exit\n");getchar();exit(0);}/*the current token is ')' */int deal_with_pointer(){ while(stack[top].type=='*'){ printf("pointer pointing to \n"); pop; } if(stack[top].type!='('){ printf(" missing an '(' after %s\n",stack[top].string ); parse_error(); } else{ pop; return 1; }}/*the current token is '('*/int deal_with_function(){ while(this.type!=')'){ gettoken(); if(this.type=='\0'){ printf(" missing an ')' before %s",this.string); parse_error(); } } printf(" function returning "); return 1;}int move_left(){ while(top>=0){ switch (stack[top].type){ case '*': printf(" pointer pointing to ");break; case QUALIFIER: printf(" %s ",stack[top].string );break; case TYPE: printf(" %s ",stack[top].string );break; default :printf("there is someting wrong about %s",stack[top].string);parse_error();break; } top--; }}