刪除C語言程序中所有的注釋語句，代碼實現
來源：程序員人生 發布時間：2015-01-19 09:05:54 閱讀次數：2593次
原文鏈接：http://lixing123.com/archives/310
學習《C程序設計語言》到第1章最后，有1道題目：
編寫1個刪除C語言程序中所有的注釋語句。要正確處理帶引號的字符串與字符常量。在C語言中,注釋不允許嵌套。
Exercise 1⑵3. Write a program to remove all comments from a C program. Don't forget to handle quoted strings and character constants properly. C comments don't nest.
剛開始，我用1種brute-force的方式，對每一個字符進行遍歷，然落后行判斷，有無進入注釋。
這樣做有1個非常麻煩的問題：只有連續檢測到“//”或"/*"時，才肯定進入了注釋狀態；如果我們只檢測到1個"/"，后面就是其它字符串的話，還得將這個單獨的"/"打印出來。
而且有許多的分支狀態，如果用if/else的話，會難以理解，并容易出錯。
在網上搜了1下，發現有1種解法非常好：狀態機。在各種狀態之間跳轉，邏輯清晰，不容易出錯，出錯了也容易調試。
下面把代碼貼出來：
#include <stdio.h>
int state;
int c1,c2;
void change_state(int c);
int main(int argc, const char * argv[]) {
int c;
state = 0;
c1 = 0;
c2 = 0;
while ((c=getchar())!=EOF) {
c1 = c2;
c2 = c;
change_state(c);
}
if (/* DISABLES CODE */ (0)==1) {
printf("just test://abcd");
printf("just test:/*hello*/");
}
}
/*狀態機函數*/
void change_state(int c){
if (state==0) {//普通狀態
if (c=='/') {
state = 1;
}else if (c=='"'){
state = 5;
putchar(c);
}else if (c=='''){
state = 6;
putchar(c);
}
else{
state = 0;
putchar(c);
}
}else if (state==1) {//檢測到1個'/'
if (c=='/') {
state = 2;
}else if (c=='*'){
state = 3;
}else{
state = 0;
putchar(c1);
putchar(c);
}
}else if (state==2) {// "//"注釋狀態
if (c=='
') {
state = 0;
putchar(c);
}else{
state = 2;
}
}else if (state==3) {// "/*"注釋狀態
if (c=='*') {
state = 4;
}else{
state = 3;
}
}else if (state==4) {
if (c=='/') {
state = 0;
}else{
state = 3;
}
}else if (state==5){//在"字符串里
if (c=='"') {
state = 0;
putchar(c);
}else if(c==''){
state = 7;
putchar(c);
}else{
state = 5;
putchar(c);
}
}else if (state==6){//在'字符里
if (c==''') {
state = 0;
putchar(c);
}else if(c==''){
state = 8;
putchar(c);
}else{
state = 6;
putchar(c);
}
}else if (state==7){//在"字符串里的""
state = 5;
putchar(c);
}else if (state==8){//在'字符串里的""
state = 6;
putchar(c);
}
}
以本段代碼作為輸入，結果以下：
#include <stdio.h>
int state;
int c1,c2;
void change_state(int c);
int main(int argc, const char * argv[]) {
int c;
state = 0;
c1 = 0;
c2 = 0;
while ((c=getchar())!=EOF) {
c1 = c2;
c2 = c;
change_state(c);
}
if ( (0)==1) {
printf("just test://abcd");
printf("just test:/*hello*/");
}
}
void change_state(int c){
if (state==0) {
if (c=='/') {
state = 1;
}else if (c=='"'){
state = 5;
putchar(c);
}else if (c=='''){
state = 6;
putchar(c);
}
else{
state = 0;
putchar(c);
}
}else if (state==1) {
if (c=='/') {
state = 2;
}else if (c=='*'){
state = 3;
}else{
state = 0;
putchar(c1);
putchar(c);
}
}else if (state==2) {
if (c=='
') {
state = 0;
putchar(c);
}else{
state = 2;
}
}else if (state==3) {
if (c=='*') {
state = 4;
}else{
state = 3;
}
}else if (state==4) {
if (c=='/') {
state = 0;
}else{
state = 3;
}
}else if (state==5){
if (c=='"') {
state = 0;
putchar(c);
}else if(c==''){
state = 7;
putchar(c);
}else{
state = 5;
putchar(c);
}
}else if (state==6){
if (c==''') {
state = 0;
putchar(c);
}else if(c==''){
state = 8;
putchar(c);
}else{
state = 6;
putchar(c);
}
}else if (state==7){
state = 5;
putchar(c);
}else if (state==8){
state = 6;
putchar(c);
}
perfect！
感謝@roma823 及其文章：http://blog.csdn.net/roma823/article/details/6364849
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