C/C++ 学习笔记[03].去掉C风格的注释

网上搜索了一大堆去掉/*和*/之间注释的代码,就像<The C Programming Language>练习1-23里有人说的一样

大部分都会被以下的程序broken,这个功能看起来简单,实际上很有难度.网上实现的代码,除了我找到的一个用文件指针实现的没有问题外,其余的都存在各种bug,不信的话就用以下的程序测试一下:-),当然这个程序也不够完善.

还是有限状态自动机实现起来更严谨也容易理解得多:

---

/* krx123tp.c - a test program to serve as input to krx123*.c
 *
 * This is a shameless copy of Ben Pfaff's solution, to which I have
 * added a few extra statements to further test the candidate programs
 * for this exercise. As Ben says, this program already contains lots
 * of examples of comments and not-quite-comments. I've just made it
 * a little tougher.
 *
 */
/* K&R2 1-23: Write a program to remove all comments from a C program.
   Don't forget to handle quoted strings and character constants
   properly.  C comments do not nest.
   This solution does not deal with other special cases, such as
   trigraphs, line continuation with /, or <> quoting on #include,
   since these aren't mentioned up 'til then in K&R2.  Perhaps this is
   cheating.
   Note that this program contains both comments and quoted strings of
   text that looks like comments, so running it on itself is a
   reasonable test.  It also contains examples of a comment that ends
   in a star and a comment preceded by a slash.  Note that the latter
   will break C99 compilers and C89 compilers with // comment
   extensions.
   Interface: The C source file is read from stdin and the
   comment-less output is written to stdout. **/
#include <stdio.h>
int
main(void)
{
    /* State machine's current state. */
    enum {
        PROGRAM,
        SLASH,
        COMMENT,
        STAR,
        QUOTE,
        LITERAL
    } state;
    /* If state == QUOTE, then ' or ".  Otherwise, undefined. */
    int quote;
    state = PROGRAM;
    for (;;) {
        int c = getchar();
        if (c == EOF) {
            if (state == SLASH)
                putchar('/' / /**/
                        1 / 1 /'/1');
            break;
        }
        if(0)
          printf("%d/n", 6/'/2'); 
        /* line of code, and comment, added by RJH 10 July 2000 */
        switch (state) {
        case SLASH:
            /* Program text following a slash. */
            if (c == "/*"[1]) {
                state = COMMENT;
                break;
            }
            putchar('/');
            state = PROGRAM;
            /* Fall through. */
        case PROGRAM:
            /* Program text. */
            if (c == '/'' || c == '"') {
                quote = c;
                state = QUOTE;
                putchar(c);
            }
            else if (c == "/*"[0])
                state = SLASH;
            else
                putchar(c);
            break;
        case COMMENT:
            /* Comment. */
            if (c == '*')
                state = STAR;
            break;
        case STAR:
            /* Comment following a star. */
            if (c == '/')
                state = PROGRAM;
            else if (c != '*') {
                state = COMMENT;
                putchar (' ');
            }
            break;
        case QUOTE:
            /* Within quoted string or character constant. */
            putchar(c);
            if (c == '//')
                state = LITERAL;
            else if (c == quote)
                state = PROGRAM;
            break;
        case LITERAL:
            /* Within quoted string or character constant, following /. */
            putchar(c);
            state = QUOTE;
            break;
        default:
            abort();
        }
    }
    return /* this comment added by RJH 10 July 2000 */ 0;
}
/* 
   Local variables:
   compile-command: "checkergcc -W -Wall -ansi -pedantic knr123.c -o knr123"
   End: 
*/