用C语言写SLR(1)分析
时间: 2023-12-14 11:39:15 浏览: 74
SLR(1)分析是一种自底向上的语法分析方法,它是一种比较简单实用的语法分析方法。下面我将介绍如何用C语言实现SLR(1)分析。
SLR(1)分析的关键是构造LR(0)自动机,并对其进行增广,然后构造SLR(1)分析表。下面是具体实现步骤:
1. 定义文法产生式规则的数据结构:
```
typedef struct production{
char left; // 产生式左部
char right[10]; // 产生式右部
int len; // 产生式右部长度
} production;
```
2. 定义LR(0)自动机状态的数据结构:
```
typedef struct state{
int id; // 状态编号
int item_num; // 项目数
int items[20]; // 项目编号
int action[128]; // 移进/规约动作
int go_to[10]; // 转移状态
} state;
```
3. 构造LR(0)自动机:
```
int goto_table[20][10]; // 转移表
state states[20]; // 状态表
int state_num = 0; // 状态数
void closure(int items[], int *item_num){
// 计算闭包
}
void goto(int items[], int item_num, int x, int *new_items, int *new_item_num){
// 计算转移
}
void construct_LR0_automaton(){
// 初始化第一个状态
int items[20] = {0};
items[0] = 1;
int item_num = 1;
closure(items, &item_num);
states[state_num].id = state_num;
states[state_num].item_num = item_num;
for(int i = 0; i < item_num; i++){
states[state_num].items[i] = items[i];
}
state_num++;
// 构造其他状态
for(int i = 0; i < state_num; i++){
for(char x = 'A'; x <= 'Z'; x++){
int new_items[20] = {0};
int new_item_num = 0;
goto(states[i].items, states[i].item_num, x, new_items, &new_item_num);
if(new_item_num > 0){
int flag = 0;
for(int j = 0; j < state_num; j++){
if(states[j].item_num == new_item_num){
int k;
for(k = 0; k < new_item_num; k++){
if(new_items[k] != states[j].items[k]){
break;
}
}
if(k == new_item_num){
// 状态已存在
states[i].go_to[x-'A'] = states[j].id;
flag = 1;
break;
}
}
}
if(flag == 0){
// 创建新状态
closure(new_items, &new_item_num);
states[state_num].id = state_num;
states[state_num].item_num = new_item_num;
for(int k = 0; k < new_item_num; k++){
states[state_num].items[k] = new_items[k];
}
states[i].go_to[x-'A'] = state_num;
state_num++;
}
}
}
}
// 构造转移表
for(int i = 0; i < state_num; i++){
for(char x = 'A'; x <= 'Z'; x++){
if(states[i].go_to[x-'A'] != -1){
goto_table[i][x-'A'] = states[i].go_to[x-'A'];
}
}
}
}
```
4. 对LR(0)自动机进行增广:
```
void augment(){
// 添加新的起始产生式
productions[len].left = 'S';
productions[len].right[0] = start_symbol;
productions[len].len = 1;
len++;
// 修改原有产生式
for(int i = 0; i < len-1; i++){
productions[i].left++;
}
non_terminal_num++;
start_symbol = 'S';
}
```
5. 构造SLR(1)分析表:
```
int action_table[20][128]; // 分析表
int goto_table[20][10]; // 转移表
void construct_SLR1_table(){
// 初始化分析表
for(int i = 0; i < state_num; i++){
for(int j = 0; j < 128; j++){
action_table[i][j] = -1;
}
for(int j = 0; j < 10; j++){
goto_table[i][j] = -1;
}
}
// 填充分析表
for(int i = 0; i < state_num; i++){
for(int j = 0; j < productions_num; j++){
for(int k = 0; k < states[i].item_num; k++){
if(productions[j].left == items[states[i].items[k]].left && items[states[i].items[k]].dot == items[states[i].items[k]].len){
// 形如 A->α.
if(productions[j].left == start_symbol){
// 接受状态
action_table[i][END] = ACCEPT;
}else{
// 规约状态
for(int l = 0; l < terminal_num; l++){
if(follow[productions[j].left-'A'][l] == 1){
action_table[i][l+'a'] = j;
}
}
}
}
}
}
for(char x = 'a'; x <= 'z'; x++){
if(states[i].go_to[x-'a'] != -1){
// 移进状态
action_table[i][x] = SHIFT;
action_table[i][x] += states[i].go_to[x-'a'];
}
}
for(char x = 'A'; x <= 'Z'; x++){
if(states[i].go_to[x-'A'] != -1){
// 转移状态
goto_table[i][x-'A'] = states[i].go_to[x-'A'];
}
}
}
}
```
6. 进行语法分析:
```
void syntax_analysis(char *input){
int stack[100] = {0};
int top = 0;
stack[top] = 0;
int ptr = 0;
while(1){
int state = stack[top];
char ch = input[ptr];
int action = action_table[state][ch];
if(action == SHIFT){
top++;
stack[top] = goto_table[state][ch-'a'];
ptr++;
}else if(action == ACCEPT){
printf("Accept\n");
break;
}else if(action >= 0){
int len = strlen(productions[action].right);
for(int i = 0; i < len; i++){
top--;
}
int new_state = stack[top];
stack[top+1] = action_table[new_state][productions[action].left];
top++;
}else{
printf("Error\n");
break;
}
}
}
```
以上是用C语言实现SLR(1)分析的基本步骤,具体实现还需要根据实际情况进行调整。