简单的FOLLOW集演示程序

 /*
  * 该程序用于计算某个非终结符的 FOLLOW 集合
  * RexfieldVon
  * 2013年6月30日16:02:47
  */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 /* 三级指针
  * 第一级指向整个产生式组
  * 第二级指向单个产生式
  * 第三级指向产生式符号单元
  * 约定：所有的大写字母为非终结符
  * 假设：无左递归、FIRST集中不会出现重复符号
  */
 char*** GrammerRule;

 /*
  * 初始化文法序列
  */
 void InitizationGrammerRule()
 {
     // 分配表头空间
     GrammerRule = (char***)malloc(sizeof(int) * );
     memset(GrammerRule, '\0', sizeof(int) * );
     // 分配文法空间并写入产生式
     // G -> E
     GrammerRule['G'] = (char**)malloc(sizeof(int) * );
     GrammerRule['G'][] = (char*)malloc();
     memcpy(GrammerRule['G'][], "E\0", );        // E
     GrammerRule['G'][] = NULL;
     // E -> T F
     GrammerRule['E'] = (char**)malloc(sizeof(int) * );
     GrammerRule['E'][] = (char*)malloc();
     memcpy(GrammerRule['E'][], "TF\0", );        // T F
     GrammerRule['E'][] = NULL;
     // F -> '+' T F | '-' T F | e
     GrammerRule['F'] = (char**)malloc(sizeof(int) * );
     GrammerRule['F'][] = (char*)malloc();
     memcpy(GrammerRule['F'][], "+TF\0", );    // '+' T F
     GrammerRule['F'][] = (char*)malloc();
     memcpy(GrammerRule['F'][], "-TF\0", );    // '-' T F
     GrammerRule['F'][] = (char*)malloc();
     memcpy(GrammerRule['F'][], "\0", );        // e （该产生式存在但是为空）
     GrammerRule['F'][] = NULL;
     // T -> A U
     GrammerRule['T'] = (char**)malloc(sizeof(int) * );
     GrammerRule['T'][] = (char*)malloc();
     memcpy(GrammerRule['T'][], "AU\0", );        // A U
     GrammerRule['T'][] = NULL;
     // U -> '*' A U | '/' A U | e
     GrammerRule['U'] = (char**)malloc(sizeof(int) * );
     GrammerRule['U'][] = (char*)malloc();
     memcpy(GrammerRule['U'][], "*AU\0", );    // '*' A U
     GrammerRule['U'][] = (char*)malloc();
     memcpy(GrammerRule['U'][], "/AU\0", );    // '/' A U
     GrammerRule['U'][] = (char*)malloc();
     memcpy(GrammerRule['U'][], "\0", );        // e （该产生式存在但是为空）
     GrammerRule['U'][] = NULL;
     // A -> '(' E ')' | d | n
     GrammerRule['A'] = (char**)malloc(sizeof(int) * );
     GrammerRule['A'][] = (char*)malloc();
     memcpy(GrammerRule['A'][], "(E)\0", );    // '(' E ')'
     GrammerRule['A'][] = (char*)malloc();
     memcpy(GrammerRule['A'][], "d\0", );        // d
     GrammerRule['A'][] = (char*)malloc();
     memcpy(GrammerRule['A'][], "n\0", );        // n
     GrammerRule['A'][] = NULL;
 }

 /*
  * 取得终结符数量
  */
 int GetTerminalCount()
 {
     int i, TerminalCount = ;
     for (i = ; i < ; i++)
     {
         if (GrammerRule[i] != NULL)
         {
             int k = ;
             while (GrammerRule[i][k] != NULL)
             {
                 int n = ;
                 while (GrammerRule[i][k][n] != '\0')
                 {
                     char c = GrammerRule[i][k][n];
                     if (c < 'A' || c > 'Z')
                     {
                         TerminalCount++;
                     }
                     n++;
                 }
                 k++;
             }
         }
     }
     return TerminalCount;
 }

 /*
  * 递归取得 FIRST 集
  * Token : char 需要打印的符号
  * FIRST : char* FIRST集
  * Ptr : int* FIRST集的位置指针
  */
 void GetFIRST(char Token, char *FIRST, int *Ptr)
 {
     if (Token >= 'A' && Token <= 'Z' && GrammerRule[Token] != NULL)
     {
         int i = ;
         while (GrammerRule[Token][i] != NULL)
         {
             GetFIRST(GrammerRule[Token][i++][], FIRST, Ptr);
         }
     }
     else if (Token < 'A' || Token > 'Z')
     {
         FIRST[*Ptr] = Token;
         *Ptr = *Ptr + ;
     }
 }

 /*
  * 添加符号到 FOLLOW 集
  * FOLLOW : char* FOLLOW集
  * Ptr : int* FOLLOW集的位置指针
  * NewItem : char 将加入的符号
  */
 void AddFOLLOWItem(char *FOLLOW, int *Ptr, char NewItem)
 {
     int i = ;
     for (; i < *Ptr; i++)
     {
         if (FOLLOW[i] == NewItem)
         {
             return ;
         }
     }
     FOLLOW[*Ptr] = NewItem;
     *Ptr = *Ptr + ;
 }

 /*
  * 取得 FOLLOW 集
  * Unterminal : char 需要打印的非终结符
  * FOLLOW : char* FOLLOW集
  * Ptr : int* FOLLOW集的位置指针
  * TerminalCount : int 终结符数量
  */
 void GetFOLLOW(char Unterminal, char *FOLLOW, int *Ptr, int TerminalCount)
 {
     int RuleIndex, ExprIndex, TokenIndex;
     // 开始遍历整个文法
     for (RuleIndex = ; RuleIndex < ; RuleIndex++)
     {
         if (GrammerRule[RuleIndex] == NULL)
         {
             continue;
         }
         // 搜索整个文法找到指定的非终结符
         for (ExprIndex = ; GrammerRule[RuleIndex][ExprIndex] != ; ExprIndex++)
         {
             for (TokenIndex = ; GrammerRule[RuleIndex][ExprIndex][TokenIndex] != '\0'; TokenIndex++)
             {
                 if (GrammerRule[RuleIndex][ExprIndex][TokenIndex] == Unterminal)
                 {
                     char nc = GrammerRule[RuleIndex][ExprIndex][TokenIndex + ];
                     if (nc == '\0' && RuleIndex != Unterminal)        // 情形三：反复计算：将FOLLOW(P)加入FOLLOW(U)
                     {
                         GetFOLLOW((char)RuleIndex, FOLLOW, Ptr, TerminalCount);
                     }
                     else if (nc >= 'A' && nc <= 'Z')    // 情形二：间接计算：将FIRST(P)加入FOLLOW(U)
                     {
                         char *FIRST = (char*)malloc(TerminalCount + );
                         memset(FIRST, '\0', TerminalCount + );
                         int FIRSTPtr = , InsertPtr;
                         GetFIRST(nc, FIRST, &FIRSTPtr);
                         for (InsertPtr = ; InsertPtr < FIRSTPtr; InsertPtr++)
                         {
                             if (FIRST[InsertPtr] != '\0')
                             {
                                 AddFOLLOWItem(FOLLOW, Ptr, FIRST[InsertPtr]);
                             }
                             else    // 对于 P->... U B，FOLLOW ← FIRST(B) - <e> + FOLLOW(P)
                             {
                                 GetFOLLOW((char)RuleIndex, FOLLOW, Ptr, TerminalCount);
                             }
                         }
                     }
                     else if (nc != '\0')    // 情形一：直接计算：将终结符加入FOLLOW(U)
                     {
                         AddFOLLOWItem(FOLLOW, Ptr, nc);
                     }
                 }
             }
         }
     }
 }

 /*
  * 打印指定非终结符的 FOLLOW 集
  * Unterminal : char 需要打印的非终结符
  * TerminalCount : int 终结符数量
  */
 void PrintUnterminalFOLLOW(char Unterminal, int TerminalCount)
 {
     char *FOLLOW = (char*)malloc(TerminalCount + );
     memset(FOLLOW, '\0', TerminalCount + );
     int Ptr = , i;
     FOLLOW[Ptr++] = '\377';        // 初始化第一个符号为 EOF
     GetFOLLOW(Unterminal, FOLLOW, &Ptr, TerminalCount);
     printf("FOLLOW(%c): ", Unterminal);
     for (i = ; i < Ptr; i++)
     {
         if (FOLLOW[i] == '\377')
         {
             printf("<eof> ");
         }
         else
         {
             printf("%c ", FOLLOW[i]);
         }
     }
     printf("\n");
 }

 int main(int argc, char **argv)
 {
     InitizationGrammerRule();    // 初始化文法
     int TerminalCount = GetTerminalCount();
     PrintUnterminalFOLLOW('E', TerminalCount);
     PrintUnterminalFOLLOW('F', TerminalCount);
     PrintUnterminalFOLLOW('T', TerminalCount);
     PrintUnterminalFOLLOW('U', TerminalCount);
     PrintUnterminalFOLLOW('A', TerminalCount);
     return ;
 }