预测分析法进行语法分析（编译原理）

预测分析法是一种表驱动的方法，它由下推栈，预测分析表和控制程序组成。实际上是一种下推自动机的实现模型。预测分析法的关键为预测分析表的构建，即文法中各非终结符first集和follow集的求得。预测分析法从开始符号开始，根据当前句型的最左边的非终结符和分析串中的当前符号，查预测分析表确定下一步推导所要选择的产生式，最终得到输入串的最左推导，完成输入串的语法检查。

其中主要建立first集，follow集合用来消除左递归（较难）

输入文本：

E T F

+ * ( ) i

E->E+T|T

T->T*F|F

F->(E)|i

(i)*i

(i)*iii

源码（C语言版）

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

#ifndef success
#define success 1
#endif

#define MAX_AMOUNT 20

/*定义非终结符*/
typedef struct NOterminal
{
char character;
int  first_number;/*FIRST集的判定，初始为0*/
int  follow_number;/*FOLLOW集的判定，初始为0*/
char * FIRST;/*FIRST 集合*/
char * FOLLOW;/*FOLLOW集合*/
struct NOterminal *next;
} noterminal;

/*定义终结符*/
typedef struct Terminal
{
char  character;/*当前的字符*/
struct Terminal *next;
} terminal;

/*定义产生式*/
typedef struct PRODUCTION
{
char source;/*产生的开始*/
char * result;/*产生的结果*/
struct PRODUCTION *next;/*指向下一条`*/
} production;

int amount=0;
char TEST_STACK[20];
char* TEST_LIST[10];
char terminal_all[10]= {0};
terminal   TERMINAL_HEAD,   *current_terminal=&TERMINAL_HEAD;
noterminal NOTERMINAL_HEAD, *current_noterminal=&NOTERMINAL_HEAD;
production PRODUCTION_HEAD, *current_production=&PRODUCTION_HEAD;

/*函数申明*/
size_t read(void);
size_t test(void);
size_t write(void);
void Test_read(void);
size_t STACK_FULL();
void STACK_POP(void);
size_t STACK_EMPTY();
void init_stack(void);
void prediction(void);
void test_follow(void);
void emergency(int model);
void prediction_table(void);
void STACK_PUSH(char source);
void insert_to_terminal(char get);
void insert_to_noterminal(char get);
void eliminate_left_recursion(void);
void combine(char* destinction,char* source);
size_t is_appeared(char tobejudged,char*source);
void insert_to_production(char source , char* result);
size_t find_first(noterminal* this_noterminal,production *this_production);
size_t find_follow(noterminal* this_noterminal,production *this_production);

int main(void)
{
TERMINAL_HEAD.next=NULL;
NOTERMINAL_HEAD.next=NULL;
PRODUCTION_HEAD.next=NULL;
read();
Test_read();
printf("\n消除左递归\n\n");
eliminate_left_recursion();

Test_read();

printf("\n求FIRST集\n\n");
prediction();
printf("\n求FOLLOW集\n\n");
test_follow();
prediction_table();
emergency(0);
return 0;
}

/*读文件*/
size_t read(void)
{
int line=0,model=0,old_line=0;
int number=0;
char current_get=0,read_temp[10]= {0};
FILE * read_stream=fopen("test1.txt","r");
if(!read_stream)
{
printf("error in open file ,can`t open file\n");
exit(EXIT_FAILURE);
}
insert_to_terminal('#');/*插入栈底元素，以#表示栈底*/
insert_to_terminal('^');/*插入空串元素，以^表示栈底*/
while(!feof(read_stream))
{
current_get=fgetc(read_stream);
while(current_get==' ')
current_get=fgetc(read_stream);/*忽略空格*/
while(current_get=='\n')
{
current_get=fgetc(read_stream);
line++;/*跳过换行*/
}

switch(line)
{
case 0:
insert_to_noterminal(current_get);
break;
case 1:
insert_to_terminal(current_get);
break;
case 3:
ungetc(current_get,read_stream);
old_line=1;
break;
default:
perror("error in format of program \n");
emergency(0);
break;
}
if(old_line)
break;
}
while(!feof(read_stream))
{
memset(read_temp,0,sizeof(read_temp));
old_line=line;
current_get=fgetc(read_stream);
while(current_get==' ')
current_get=fgetc(read_stream);/*忽略空格*/
while(current_get=='\n')
{
current_get=fgetc(read_stream);
line++;/*跳过换行*/
}
model=((line-old_line)>model)? (line-old_line): model;
switch(model)
{
case 0:
case 1:
fscanf(read_stream,"%s",read_temp);
insert_to_production(current_get,read_temp);
break;
case 2:
ungetc(current_get,read_stream);
TEST_LIST[number]=(char*)malloc(20);
memset(TEST_LIST[number],0,20);
fscanf(read_stream,"%s",TEST_LIST[number++]);
break;
default:
perror("error in format of program \n");
emergency(1);
break;
}
}

fclose(read_stream);
return success;
}
/*测试*/
size_t test(void)
{
noterminal *TEMP_NOTERMINAL=NOTERMINAL_HEAD.next;

for(; TEMP_NOTERMINAL!=NULL; TEMP_NOTERMINAL=TEMP_NOTERMINAL->next)
{
printf("%c\tfirst number=%d\tfirst=%s\n",
TEMP_NOTERMINAL->character,
TEMP_NOTERMINAL->first_number,
TEMP_NOTERMINAL->FIRST);
}
printf("\n");
return success;
}

/*求FIRST集合*/
size_t find_first(noterminal* this_noterminal,production *this_production)
{
noterminal* this_noterminal_temp;
char temp[2]= {0};
char *TEMP2,*help;
while(this_production->source!=this_noterminal->character)
this_production=this_production->next;/*移向下一个产生式*/

/*查看是否是第一次，如果是，分配空间*/
if(this_noterminal->first_number==0)
{
this_noterminal->FIRST=(char*)malloc(MAX_AMOUNT+1);
memset(this_noterminal->FIRST,0,MAX_AMOUNT+1);
}
while(this_production&&this_production->source==this_noterminal->character)
{
TEMP2=this_production->result;
while(*TEMP2)
{
if(is_appeared(*TEMP2,terminal_all))
{
temp[0]=this_production->result[0];
combine(this_noterminal->FIRST,temp);
break;
}
else
{
this_noterminal_temp=NOTERMINAL_HEAD.next;
while(this_noterminal_temp->character!=*TEMP2)
this_noterminal_temp=this_noterminal_temp->next;
if(this_noterminal_temp->first_number==0)/*没求first集*/
find_first(this_noterminal_temp,PRODUCTION_HEAD.next);
combine(this_noterminal->FIRST,this_noterminal_temp->FIRST);
help=this_noterminal->FIRST;
while(*help&&*help!='^')
help++;
if(*help&&*(TEMP2+1))/*包含'^'*/
{
while(*help)
{
*help=*(help+1);
help++;
}
}
else break;
TEMP2++;
}
}
this_production=this_production->next;
}
this_noterminal->first_number=strlen(this_noterminal->FIRST);
return success;
}

/*求FOLLOW集合*/
size_t find_follow(noterminal* this_noterminal,production *this_production)
{
char* help=NULL;
char* temp_result;
int symbol=0;
char terminal_array[2]= {0};
noterminal* FOLLOW_TEMP,*FOLLOW_HELP;

if(this_noterminal->follow_number==0)
{
this_noterminal->FOLLOW=(char* )malloc(MAX_AMOUNT+1);
memset(this_noterminal->FOLLOW,0,MAX_AMOUNT+1);
}

/*第一个非终结符包含有#*/
if(this_noterminal==NOTERMINAL_HEAD.next)
*this_noterminal->FOLLOW='#';

while(this_production)
{
temp_result=this_production->result;
/*一个产生式未结尾*/
while(*temp_result)
{
if(*temp_result!=this_noterminal->character)
{
temp_result++;
continue;
}
temp_result++;
if(!*temp_result)
symbol=1;
while(*temp_result)
{
if(is_appeared(*temp_result,terminal_all))
{
terminal_array[0]=*temp_result;
combine(this_noterminal->FOLLOW,terminal_array);
}
else
{
FOLLOW_TEMP=NOTERMINAL_HEAD.next;
while(FOLLOW_TEMP->character!=*temp_result)
FOLLOW_TEMP=FOLLOW_TEMP->next;
combine(this_noterminal->FOLLOW,FOLLOW_TEMP->FIRST);
help=this_noterminal->FOLLOW;
while(*help&&*help!='^')
help++;
if(*help)/*包含'^'*/
{
while(*help)
{
*help=*(help+1);
help++;
}
symbol=1;
}
else
{
symbol=0;
break;
}
}
temp_result++;
}
if(symbol&&this_production->source!=this_noterminal->character)
{
FOLLOW_HELP=NOTERMINAL_HEAD.next;
while(FOLLOW_HELP->character!=this_production->source)
FOLLOW_HELP=FOLLOW_HELP->next;
if(FOLLOW_HELP->follow_number==0)
find_follow(FOLLOW_HELP,PRODUCTION_HEAD.next);
combine(this_noterminal->FOLLOW,FOLLOW_HELP->FOLLOW);
symbol=0;
}
}
this_production=this_production->next;
}
this_noterminal->follow_number=strlen(this_noterminal->FOLLOW);
return success;
}

/*紧急退出*/
void emergency(int model)
{
current_noterminal=NOTERMINAL_HEAD.next;
current_terminal=TERMINAL_HEAD.next;
current_production=PRODUCTION_HEAD.next;
while(current_noterminal)
{
NOTERMINAL_HEAD.next=current_noterminal->next;
free(current_noterminal->FIRST);
free(current_noterminal->FOLLOW);
free(current_noterminal);
current_noterminal=NOTERMINAL_HEAD.next;
}
while(current_terminal)
{
TERMINAL_HEAD.next=current_terminal->next;
free(current_terminal);
current_terminal=TERMINAL_HEAD.next;
}
while(current_production)
{
PRODUCTION_HEAD.next=current_production->next;
free(current_production->result);
free(current_production);
current_production=PRODUCTION_HEAD.next;
}
printf("退出成功\n");
exit(0);
}

/*插入到终结符*/
void insert_to_terminal(char get)
{
terminal *Temp_terminal=(terminal*)malloc(sizeof(terminal));
if(!Temp_terminal)
{
perror("can`t malloc for this program\n");
emergency(0);
}
Temp_terminal->character=get;
Temp_terminal->next=NULL;
current_terminal->next=Temp_terminal;
current_terminal=Temp_terminal;/*移向下一个节点*/
return ;
}

/*插入到非终结符*/
void insert_to_noterminal(char get)
{
noterminal *Temp_noterminal=(noterminal*)malloc(sizeof(noterminal));
if(!Temp_noterminal)
{
perror("can`t malloc for this program\n");
emergency(0);
}
Temp_noterminal->character=get;
Temp_noterminal->next=NULL;
Temp_noterminal->FIRST=NULL;
Temp_noterminal->FOLLOW=NULL;
Temp_noterminal->first_number=0;
Temp_noterminal->follow_number=0;
current_noterminal->next=Temp_noterminal;
current_noterminal=Temp_noterminal;/*移向下一个节点*/
return ;
}

/*插入到产生式*/
void insert_to_production(char source , char* result)
{

char TEMP[20]= {0};
int COUNT=0,number=0,length=0,exit_condition=strlen(result);
production *Temp_production;
for (COUNT=0; COUNT!=exit_condition+1; COUNT++)
{
if(*result=='-'&&*(result+1)=='>')
{
result+=2;
COUNT+=2;
}
if((*result!='|')&&(*result))
TEMP[number++]=*result;
else
{
Temp_production=(production*)malloc(sizeof(production));
length=strlen(TEMP)+1;
Temp_production->result=(char* )malloc(length);
memset(Temp_production->result,0,length);
strncpy(Temp_production->result,TEMP,length-1);
memset(TEMP,0,sizeof(TEMP));
Temp_production->source=source;
Temp_production->next=NULL;
current_production->next=Temp_production;
current_production=Temp_production;
number=0;
}
result++;
}
return ;
}

/*消除左递归*/
void eliminate_left_recursion(void)
{
int number=0;
char new_char[3]= {0},TEMP_RESULT[20],temp_empty[3]= {'^',0,0};
production  *Temp_production=PRODUCTION_HEAD.next;
production  *Temp_FREE;
terminal *temp=TERMINAL_HEAD.next;
while(Temp_production)
{
if(Temp_production->source==Temp_production->result[0])
{
memset(TEMP_RESULT,0,sizeof(TEMP_RESULT));
new_char[0]=Temp_production->source-'A'+'a';
/*复制到新的产生式*/
strcat(TEMP_RESULT,Temp_production->result+1);
strcat(TEMP_RESULT,new_char);
insert_to_noterminal(new_char[0]);
insert_to_production(new_char[0],TEMP_RESULT);
insert_to_production(new_char[0],temp_empty);

/*修改当前的产生式*/
memset(TEMP_RESULT,0,sizeof(TEMP_RESULT));
strcat(TEMP_RESULT,Temp_production->next->result);
strcat(TEMP_RESULT,new_char);
memset(Temp_production->result,0,strlen(Temp_production->result));
strncpy(Temp_production->result,TEMP_RESULT,strlen(TEMP_RESULT));

Temp_FREE= Temp_production->next;
Temp_production->next=Temp_production->next->next;
free(Temp_FREE);
continue;
}
Temp_production=Temp_production->next;
}
while(temp)
{
terminal_all[number++]=temp->character;
temp=temp->next;
}
return ;
}

void Test_read(void)
{
int number=1;
production *TEMP_PRODUCTION=PRODUCTION_HEAD.next;
terminal *TEMP_TERMINAL=TERMINAL_HEAD.next;
noterminal *TEMP_NOTERMINAL=NOTERMINAL_HEAD.next;

printf("\n产生式\n");
for(number=1; TEMP_PRODUCTION!=NULL; TEMP_PRODUCTION=TEMP_PRODUCTION->next,number++)
{
printf("%d\t%c\t%s\n",number,TEMP_PRODUCTION->source,TEMP_PRODUCTION->result);
}
printf("\n终结符\n");
for(; TEMP_TERMINAL!=NULL; TEMP_TERMINAL=TEMP_TERMINAL->next)
{
printf("%c\t",TEMP_TERMINAL->character);
}
printf("\n");
printf("\n非终结符\n");
for(; TEMP_NOTERMINAL!=NULL; TEMP_NOTERMINAL=TEMP_NOTERMINAL->next)
{
printf("%c\t",TEMP_NOTERMINAL->character);
}
printf("\n读取测试\n%s\n%s\n",TEST_LIST[0],TEST_LIST[1]);
printf("\n");
return ;
}

size_t is_appeared(char tobejudged,char*source)
{
size_t length=strlen(source),counts=0;
while((counts!=length)&&(*source!=tobejudged))
{
counts++;
source++;
}
return counts==length?!success: success;
}

void combine(char* destinction,char* source)
{
char temp[2]= {0};
while(*source)
{
if(!is_appeared(*source,destinction))
{
temp[0]=*source;
strcat(destinction,temp);
}
source++;
}
return ;
}

void prediction(void)
{
noterminal* TEMP_NOTERMINAL=NOTERMINAL_HEAD.next;
while(TEMP_NOTERMINAL!=NULL)
{
find_first(TEMP_NOTERMINAL,PRODUCTION_HEAD.next);
TEMP_NOTERMINAL=TEMP_NOTERMINAL->next;
}
test();

TEMP_NOTERMINAL=NOTERMINAL_HEAD.next;
while(TEMP_NOTERMINAL!=NULL)
{
find_follow(TEMP_NOTERMINAL,PRODUCTION_HEAD.next);
TEMP_NOTERMINAL=TEMP_NOTERMINAL->next;
}
return ;
}

void test_follow(void)
{
noterminal *TEMP_NOTERMINAL=NOTERMINAL_HEAD.next;

for(; TEMP_NOTERMINAL!=NULL; TEMP_NOTERMINAL=TEMP_NOTERMINAL->next)
{
printf("%c\tfollow number=%d\tfollow=%s\n",
TEMP_NOTERMINAL->character,
TEMP_NOTERMINAL->follow_number,
TEMP_NOTERMINAL->FOLLOW);
}
printf("\n");
return ;
}

void prediction_table(void)
{
int line=0,row=0,current_character=0,number=0;
char* FIRST_CLUM,*test_exper;
noterminal* temp_noterminal=NOTERMINAL_HEAD.next,*temp_noterminal21;
terminal*   temp_terminal=TERMINAL_HEAD.next;
production* temp_production=PRODUCTION_HEAD.next;
char hah[5][7];
memset(hah,0,sizeof(hah));
for(line=0; line<5; line++)
{
for(row=0; row<7; row++)
hah[line][row]=0;
}
line=0;
while(temp_production)
{
row=0;
if(is_appeared(*temp_production->result,terminal_all)&&(*temp_production->result!='^'))
{
while(terminal_all[row]!=*temp_production->result)
row++;
hah[current_character][row]=line+1;
}
else
{
temp_noterminal=NOTERMINAL_HEAD.next;
if(*temp_production->result=='^')
{
while(temp_noterminal->character!=temp_production->source)
temp_noterminal=temp_noterminal->next;
FIRST_CLUM=temp_noterminal->FOLLOW;

if(is_appeared('#',FIRST_CLUM))
{
row=0;
while(terminal_all[row] != '#')
row++;
hah[current_character][row]=line+1;
}
while(*FIRST_CLUM)
{
row=0;
while(terminal_all[row]!=*FIRST_CLUM)
row++;
hah[current_character][row]=line+1;
FIRST_CLUM++;
}
if(temp_production->next&&temp_production->source!=temp_production->next->source)
current_character++;
temp_production=temp_production->next;
line++;
continue;
}
/*是非终结符*/
while(temp_noterminal->character!=*temp_production->result)
temp_noterminal=temp_noterminal->next;
FIRST_CLUM=temp_noterminal->FIRST;
while(*FIRST_CLUM)
{
row=0;
while(terminal_all[row]!=*FIRST_CLUM)
row++;
hah[current_character][row]=line+1;
FIRST_CLUM++;
}
temp_noterminal21=NOTERMINAL_HEAD.next;
while(temp_noterminal21->character!=temp_production->source)
temp_noterminal21=temp_noterminal21->next;
if(is_appeared('^',temp_noterminal->FIRST)&&is_appeared('#',temp_noterminal21->FOLLOW))
{
row=0;
while(terminal_all[row]!=*FIRST_CLUM)
row++;
hah[line][row]=line+1;
FIRST_CLUM++;
}
}
if(temp_production->next&&temp_production->source!=temp_production->next->source)
current_character++;
temp_production=temp_production->next;
line++;
}

printf("\n预测分析表\n\n");
printf(" \t");
for(temp_terminal=TERMINAL_HEAD.next; temp_terminal; temp_terminal=temp_terminal->next)
printf("%c\t",temp_terminal->character);
temp_noterminal=NOTERMINAL_HEAD.next;
for(line=0; line<5; line++)
{
printf("\n%c\t",temp_noterminal->character);
for(row=0; row<7; row++)
printf("%c\t",hah[line][row]==0?' ':(hah[line][row]-0+'0'));
temp_noterminal=temp_noterminal->next;
}
printf("\n\n");
system("pause");
printf("\n\n");
memset(TEST_STACK,0,sizeof(TEST_STACK));
init_stack();
test_exper=TEST_LIST[0];
test_exper[strlen(test_exper)]='#';
STACK_PUSH(NOTERMINAL_HEAD.next->character);
while(!STACK_EMPTY())
{
printf("分析栈\t");
for(number=0; number<=amount; number++)
printf("%c",TEST_STACK[number]);
printf("\t剩余字符串\t%s\n",test_exper);
if(TEST_STACK[amount]==*test_exper)
{
STACK_POP();
test_exper++;
}
else
{
line=0;
row=0;
temp_noterminal=NOTERMINAL_HEAD.next;
while(temp_noterminal->character!=TEST_STACK[amount])
{
temp_noterminal=temp_noterminal->next;
line++;
}
while(terminal_all[row]!=*test_exper)
row++;
row=hah[line][row];
if(!row)
break;
temp_production=PRODUCTION_HEAD.next;
while(--row)
temp_production=temp_production->next;

FIRST_CLUM=temp_production->result;
current_character=strlen(FIRST_CLUM);
FIRST_CLUM=FIRST_CLUM+current_character-1;
STACK_POP();
while(current_character)
{
if(*FIRST_CLUM!='^')
STACK_PUSH(*FIRST_CLUM);
FIRST_CLUM--;
current_character--;
}
}
}

printf("分析栈\t");
for(number=0; number<=amount; number++)
printf("%c",TEST_STACK[number]);
printf("\t剩余字符串\t%s\n",test_exper);
if(STACK_EMPTY()&&*test_exper=='#')
printf("\n合法输入\n");
else
printf("\n不合法输入\n");
return ;
}

void STACK_POP(void)
{
if(STACK_EMPTY())
{
printf("栈空\n");
emergency(2);
}
amount--;
return ;
}
size_t STACK_EMPTY()
{
return amount==0? success:!success;
}
size_t STACK_FULL()
{
return amount==19? success:!success;
}
void STACK_PUSH(char source)
{
if(STACK_FULL())
{
printf("栈满\n");
emergency(2);
}
TEST_STACK[++amount]=source;
return ;
}

void init_stack(void)
{
amount=0;
TEST_STACK[amount]='#';
return ;
}

运行结果：