用C++编写一个LL1语法分析器
时间: 2023-08-21 15:04:17 浏览: 106
下面是一个基于C++的LL(1)语法分析器示例代码,仅供参考:
```c++
#include <iostream>
#include <string>
#include <vector>
#include <stack>
using namespace std;
// 预测分析表
char parsing_table[10][10] = {
/* E T F + * ( ) i $ */
{'1', ' ', ' ', ' ', ' ', '2', ' ', '3', ' ', ' '}, // E
{' ', '4', ' ', '5', ' ', ' ', ' ', ' ', '6', ' '}, // T
{'7', ' ', '8', ' ', ' ', '9', ' ', ' ', '10', ' '}, // F
};
// 产生式
string productions[10] = {
"E->T+E",
"E->T",
"T->F*T",
"T->F",
"F->(E)",
"F->i",
};
// 输入缓冲区
string buffer;
// 符号栈
stack<char> stk;
// LL(1)语法分析
void parse() {
stk.push('$');
stk.push('E');
int buf_idx = 0;
char lookahead = buffer[buf_idx];
while (!stk.empty()) {
char top_char = stk.top();
if (top_char == lookahead) {
cout << "Match " << lookahead << endl;
stk.pop();
buf_idx++;
if (buf_idx < buffer.length()) {
lookahead = buffer[buf_idx];
} else {
lookahead = '$';
}
} else if (top_char >= 'A' && top_char <= 'Z') {
int row = top_char - 'A';
int col = lookahead - '0';
char production = parsing_table[row][col];
if (production == ' ') {
cout << "Error: Parsing table entry is empty!" << endl;
exit(1);
} else {
cout << "Apply production " << top_char << " -> " << productions[production - '0'] << endl;
stk.pop();
string rhs = productions[production - '0'].substr(3); // 获取产生式右部
if (rhs != "epsilon") {
for (int i = rhs.length() - 1; i >= 0; i--) {
stk.push(rhs[i]);
}
}
}
} else {
cout << "Error: Invalid character " << top_char << " on stack!" << endl;
exit(1);
}
}
}
int main() {
cout << "Enter input string: ";
cin >> buffer;
buffer += '$';
parse();
return 0;
}
```
该代码使用了C++的STL库中的栈,实现了LL(1)语法分析器的基本功能。用户需要输入一个待分析的字符串,程序将输出分析过程中的每个步骤,包括匹配、应用产生式等。需要注意的是,该代码只能处理特定的文法,如果需要处理其他文法,需要修改预测分析表和产生式。
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