C语言代码的语法分析实现代码

C语言的语法分析可以使用工具如Flex和Bison来实现，也可以手写代码实现。以下是手写代码实现的示例：

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

#define MAX_TOKEN_LEN 100

// Token类型
typedef enum {
    TOKEN_INT,
    TOKEN_FLOAT,
    TOKEN_PLUS,
    TOKEN_MINUS,
    TOKEN_MULTIPLY,
    TOKEN_DIVIDE,
    TOKEN_LPAREN,
    TOKEN_RPAREN,
    TOKEN_END
} TokenType;

// Token结构体
typedef struct {
    TokenType type;
    char value[MAX_TOKEN_LEN];
} Token;

// TokenStream结构体
typedef struct {
    Token tokens[MAX_TOKEN_LEN];
    int pos;
} TokenStream;

// 词法分析函数
void lex(char* input, TokenStream* ts)
{
    int i = 0, j = 0;
    while (input[i] != '\0') {
        if (input[i] == '+') {
            ts->tokens[j].type = TOKEN_PLUS;
            strcpy(ts->tokens[j].value, "+");
            j++;
        } else if (input[i] == '-') {
            ts->tokens[j].type = TOKEN_MINUS;
            strcpy(ts->tokens[j].value, "-");
            j++;
        } else if (input[i] == '*') {
            ts->tokens[j].type = TOKEN_MULTIPLY;
            strcpy(ts->tokens[j].value, "*");
            j++;
        } else if (input[i] == '/') {
            ts->tokens[j].type = TOKEN_DIVIDE;
            strcpy(ts->tokens[j].value, "/");
            j++;
        } else if (input[i] == '(') {
            ts->tokens[j].type = TOKEN_LPAREN;
            strcpy(ts->tokens[j].value, "(");
            j++;
        } else if (input[i] == ')') {
            ts->tokens[j].type = TOKEN_RPAREN;
            strcpy(ts->tokens[j].value, ")");
            j++;
        } else if (isdigit(input[i])) {
            int k = i;
            while (isdigit(input[k])) {
                k++;
            }
            if (input[k] == '.') {
                k++;
                while (isdigit(input[k])) {
                    k++;
                }
                ts->tokens[j].type = TOKEN_FLOAT;
            } else {
                ts->tokens[j].type = TOKEN_INT;
            }
            strncpy(ts->tokens[j].value, &input[i], k-i);
            ts->tokens[j].value[k-i] = '\0';
            j++;
            i = k-1;
        }
        i++;
    }
    ts->tokens[j].type = TOKEN_END;
}

// 语法分析函数
double parse_expression(TokenStream* ts);

double parse_primary(TokenStream* ts)
{
    double result = 0.0;
    if (ts->tokens[ts->pos].type == TOKEN_INT) {
        result = atoi(ts->tokens[ts->pos].value);
        ts->pos++;
    } else if (ts->tokens[ts->pos].type == TOKEN_FLOAT) {
        result = atof(ts->tokens[ts->pos].value);
        ts->pos++;
    } else if (ts->tokens[ts->pos].type == TOKEN_LPAREN) {
        ts->pos++;
        result = parse_expression(ts);
        if (ts->tokens[ts->pos].type != TOKEN_RPAREN) {
            printf("Error: expected )\n");
            exit(1);
        }
        ts->pos++;
    } else {
        printf("Error: expected number or (\n");
        exit(1);
    }
    return result;
}

double parse_term(TokenStream* ts)
{
    double left = parse_primary(ts);
    while (ts->tokens[ts->pos].type == TOKEN_MULTIPLY || ts->tokens[ts->pos].type == TOKEN_DIVIDE) {
        if (ts->tokens[ts->pos].type == TOKEN_MULTIPLY) {
            ts->pos++;
            left *= parse_primary(ts);
        } else if (ts->tokens[ts->pos].type == TOKEN_DIVIDE) {
            ts->pos++;
            left /= parse_primary(ts);
        }
    }
    return left;
}

double parse_expression(TokenStream* ts)
{
    double left = parse_term(ts);
    while (ts->tokens[ts->pos].type == TOKEN_PLUS || ts->tokens[ts->pos].type == TOKEN_MINUS) {
        if (ts->tokens[ts->pos].type == TOKEN_PLUS) {
            ts->pos++;
            left += parse_term(ts);
        } else if (ts->tokens[ts->pos].type == TOKEN_MINUS) {
            ts->pos++;
            left -= parse_term(ts);
        }
    }
    return left;
}

int main()
{
    char input[100];
    TokenStream ts;
    printf("Enter an expression: ");
    fgets(input, sizeof(input), stdin);
    input[strlen(input)-1] = '\0';
    lex(input, &ts);
    double result = parse_expression(&ts);
    printf("Result: %f\n", result);
    return 0;
}

该示例实现了一个简单的四则运算表达式解析器，包括词法分析和语法分析两个部分。程序首先读入一个表达式，然后使用lex函数将其转换为TokenStream。接着，程序调用parse_expression函数对表达式进行语法分析并计算结果。parse_expression函数内部调用parse_term和parse_primary函数来解析表达式的项和因子。如果在解析过程中发现错误，程序将输出错误信息并退出。