制作一个简单的C语言词法分析程序

1.分析组成

C语言的程序中，有很单词多符号和保留字。一些单词符号还有对应的左线性文法。所以我们需要先做出一个单词字符表，给出对应的识别码，然后跟据对应的表格来写出程序

 

2.程序设计

程序主要有循环判断构成。不需推理即可产生的符号我们可以把它包装在函数中，返回值为对应的识别码即可。但是有线性文法的则需要单独的一遍推倒才可以得出词法分析结果。对于测试样例我们可以存储到txt文件中，使用循环读写可以更高效的测试和输出词法分析结果。最终的结果我们用二元式的形式来表示，存储在txt文件中

3.完整程序

#include <stdio.h>
#include <stdlib.h>
#include <string.h>int english(char ch) {if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) return 1;else return 0;
}
int number(char ch) {if(ch >= '0' && ch <= '9') return 1;else return 0;
}
int reserved(char str[]) {if(strcmp(str, "void") == 0) return 3;else if(strcmp(str, "int") == 0) return 4;else if(strcmp(str, "float") == 0) return 5;else if(strcmp(str, "double") == 0) return 6;else if(strcmp(str, "if") == 0) return 7;else if(strcmp(str, "else") == 0) return 8;else if(strcmp(str, "for") == 0) return 9;else if(strcmp(str, "do") == 0) return 10;else if(strcmp(str, "while") == 0) return 11;else if(strcmp(str, "break") == 0) return 12;else if(strcmp(str, "return") == 0) return 13;else return 1;
}
int symbol(char ch) {if(ch == ';') return 14;else if(ch == ',') return 15;else if(ch == '(') return 16;else if(ch == ')') return 17;else if(ch == '{') return 18;else if(ch == '}') return 19;else if(ch == '[') return 20;else if(ch == ']') return 21;else if(ch == '%') return 22;else if(ch == '?') return 23;else if(ch == ':') return 24;else if(ch == '\'') return 25;else if(ch == '\"') return 26;else if(ch == '.') return 27;else return 0;
}int main(){for(int i = 1; i <= 4; i++){char txt1[] = "test";char num[6];sprintf(num, "%d.txt", i);strcat(txt1, num);char txt2[] = "analyze";sprintf(num, "%d.txt", i);strcat(txt2, num);FILE *fp = fopen(txt1, "r");FILE *fw = fopen(txt2, "wt+");int flag = 0;char ch = fgetc(fp);	while(!feof(fp)) {char str[32];int j = 0;if(ch == ' ' || ch == '\t') {ch = fgetc(fp);continue;}else if(ch == '\n'){fprintf(fw, "\n");ch = fgetc(fp);continue;}else if(english(ch)) {str[j++] = ch;do{ch = fgetc(fp);str[j++] = ch;}while(english(ch)||number(ch));str[j-1] = '\0';int id = reserved(str);fprintf(fw, "(%d, %s) ", id, str);}else if(number(ch)) {str[j++] = ch;do{ch = fgetc(fp);str[j++] = ch;}while(number(ch));str[j-1] = '\0';fprintf(fw, "(2, %s) ", str);}else if(symbol(ch) != 0) {fprintf(fw, "(%d, %c) ", symbol(ch), ch);ch = fgetc(fp);}else if(ch == '>') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(29, >=) ");ch = fgetc(fp);}else if(ch == '>') {fprintf(fw, "(30, >>) ");ch = fgetc(fp);}else fprintf(fw, "(28, >) ");}else if(ch == '<') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(32, <=) ");ch = fgetc(fp);}else if(ch == '<') {fprintf(fw, "(33, <<) ");ch = fgetc(fp);}else fprintf(fw, "(31, <) ");}else if(ch == '!') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(35, !=) ");ch = fgetc(fp);}else fprintf(fw, "(34, !) ");}else if(ch == '=') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(37, ==) ");ch = fgetc(fp);}else fprintf(fw, "(36, =) ");}else if(ch == '/') {ch = fgetc(fp);if(ch == '*') {fprintf(fw, "(Start annotate, /*) ");do {ch = fgetc(fp);if(ch == '*') {ch = fgetc(fp);if(ch == '/') {fprintf(fw, "(End annotate, */) ");ch = fgetc(fp);break;}}}while(1);}else if(ch == '/') {fprintf(fw, "(annotate, //) ");do {ch = fgetc(fp);}while(ch != '\n');fprintf(fw, "\n");ch = fgetc(fp);}else if(ch == '=') {fprintf(fw, "(39, /=) ");ch = fgetc(fp);}else fprintf(fw, "(38, /) ");}else if(ch == '&') {ch = fgetc(fp);if(ch == '&') {fprintf(fw, "(41, &&) ");ch = fgetc(fp);}else fprintf(fw, "(40, &) ");}else if(ch == '|') {ch = fgetc(fp);if(ch == '|') {fprintf(fw, "(43, ||) ");ch = fgetc(fp);}else fprintf(fw, "(42, |) ");}else if(ch == '+') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(46, +=) ");ch = fgetc(fp);}else if(ch == '+') {fprintf(fw, "(45 ++) ");ch = fgetc(fp);}else fprintf(fw, "(44, +) ");}else if(ch == '-') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(49, -=) ");ch = fgetc(fp);}else if(ch == '-') {fprintf(fw, "(48, --) ");ch = fgetc(fp);}else fprintf(fw, "(47, -) ");}else if(ch == '*') {ch = fgetc(fp);if(ch == '=') {fprintf(fw, "(51, *=) ");ch = fgetc(fp);}else fprintf(fw, "(50, *) ");}else if(ch == '\\') {ch = fgetc(fp);if(ch == 'n') {ch = fgetc(fp);}}else {fprintf(fw, "Undefined symbol!");printf("test%d: Undefined symbol!\n", i); flag = 1;break;}}fclose(fp);fclose(fw);if(flag) continue;printf("test%d: Finish analyzing.\n", i);}
} 

 4.测试运行

其中一个测试样例：（剩余的大家可以自主编写） 

void test1() {int a = 5, b = 10;if (a > b) {printf("a is greater than b");} else if (a < b) {printf("b is greater than a");} else {printf("a and b are equal");}for (int i = 0; i < 5; i++) {printf("%d ", i);}printf("\n");int arr[5] = {1, 2, 3, 4, 5};int sum = 0;for (int i = 0; i < 5; i++) {sum += arr[i];}printf("The sum of the array is: %d\n", sum);return 0;
}

 运行结果:

(3, void) (1, test1) (16, () (17, )) (18, {) 
(4, int) (1, a) (36, =) (2, 5) (15, ,) (1, b) (36, =) (2, 10) (14, ;) 
(7, if) (16, () (1, a) (28, >) (1, b) (17, )) (18, {) 
(1, printf) (16, () (26, ") (1, a) (1, is) (1, greater) (1, than) (1, b) (26, ") (17, )) (14, ;) 
(19, }) (8, else) (7, if) (16, () (1, a) (31, <) (1, b) (17, )) (18, {) 
(1, printf) (16, () (26, ") (1, b) (1, is) (1, greater) (1, than) (1, a) (26, ") (17, )) (14, ;) 
(19, }) (8, else) (18, {) 
(1, printf) (16, () (26, ") (1, a) (1, and) (1, b) (1, are) (1, equal) (26, ") (17, )) (14, ;) 
(19, }) (9, for) (16, () (4, int) (1, i) (36, =) (2, 0) (14, ;) (1, i) (31, <) (2, 5) (14, ;) (1, i) (45 ++) (17, )) (18, {) 
(1, printf) (16, () (26, ") (22, %) (1, d) (26, ") (15, ,) (1, i) (17, )) (14, ;) 
(19, }) 
(1, printf) (16, () (26, ") (26, ") (17, )) (14, ;) (4, int) (1, arr) (20, [) (2, 5) (21, ]) (36, =) (18, {) (2, 1) (15, ,) (2, 2) (15, ,) (2, 3) (15, ,) (2, 4) (15, ,) (2, 5) (19, }) (14, ;) 
(4, int) (1, sum) (36, =) (2, 0) (14, ;) 
(9, for) (16, () (4, int) (1, i) (36, =) (2, 0) (14, ;) (1, i) (31, <) (2, 5) (14, ;) (1, i) (45 ++) (17, )) (18, {) 
(1, sum) (46, +=) (1, arr) (20, [) (1, i) (21, ]) (14, ;) 
(19, }) 
(1, printf) (16, () (26, ") (1, The) (1, sum) (1, of) (1, the) (1, array) (1, is) (24, :) (22, %) (1, d) (26, ") (15, ,) (1, sum) (17, )) (14, ;) (13, return) (2, 0) (14, ;) 
(19, })