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/* Extract comments from a C program source file.
**
** This program acts as a filter to copy comments in a C source
** file to the output. Each comment includes the starting and
** ending delimiters and is followed by a newline.
**
** Three #ifdef options are defined:
** INHIBIT_TRIGRAPHS prevents recognition of trigraphs, which
** can affect detection of escaped characters,
** i.e., ??/" is an escaped quote.
** TRANSLATE_TRIGRAPHS causes the output to have trigraphs
** converted to the normal C characters.
** CPP_MODE causes "//" to start a comment.
** The default for these symbols is undefined, resulting in
** operation on strict ANSI source, except as noted below.
**
** What makes this program interesting is that comment detection
** should be inhibited within strings and character constants.
**
** Note: The name of a header following #include can, under ANSI,
** contain any sequence of characters, except \n and the closing
** > or ". This program doesn't inhibit comment, string, or character
** constant detection within the header name, as an ANSI parser must.
**
** Written by and contributed to the public domain by
** Thad Smith III, Boulder, CO, October 1990.
*/
#include <stdio.h>
#ifndef INHIBIT_TRIGRAPHS /* default: recognize trigraphs */
#define getnc() getnsc(1) /* get char with trigraph xlate */
#ifdef TRANSLATE_TRIGRAPHS
#define getcmtc() getnsc(1) /* get comment char w/ t.g. xlate */
#else
#define getcmtc() getnsc(0) /* default: no comment t.g. xlate */
#endif
/*
** get next source character or EOF
*/
int getnsc(int cvtg) /* boolean: convert trigraphs */
{
static int c, nc, nnc; /* next 3 characters */
/* shift in next source character */
c = nc; nc = nnc; nnc = getchar();
/* perform trigraph substitution */
if (cvtg && c == '?' && nc == '?')
{
switch (nnc)
{
case '=' :
c = '#' ;
break;
case '(' :
c = '[' ;
break;
case '/' :
c = '\\';
break;
case ')' :
c = ']' ;
break;
case '\'':
c = '^' ;
break;
case '<' :
c = '{' ;
break;
case '!' :
c = '|' ;
break;
case '>' :
c = '}' ;
break;
case '-' :
c = '~' ;
break;
default :
return c; /* no substitution */
}
nc = getchar(); nnc = getchar();
}
return c;
}
#else /* don't process trigraphs */
#define getnc() getchar()
#define getcmtc() getchar()
#endif
int main(void)
{
int pc; /* previous character */
int c; /* current input character */
#ifndef INHIBIT_TRIGRAPHS
getnc(); /* prime the pump */
getnc();
#endif
c = getnc(); /* get first char */
for (;;) /* in non-comment area */
{
switch (c)
{
case '/': /* possible start of comment */
if ((c= getnc()) == '*') /* process comment */
{
putchar('/');
putchar('*');
/* copy comment to stdout */
for (pc = 0; (c = getcmtc()) != EOF &&
(putchar(c) != '/' || pc != '*'); pc=c)
;
putchar('\n');
#ifdef CPP_MODE
}
else if (c == '/') /* '//' comment */
{
putchar('/');
putchar('/');
while ((c = getcmtc()) != EOF && putchar(c) != '\n')
;
#endif
}
else continue; /* test current char */
break;
case '\"': /* start of string */
case '\'': /* start of (possibly multi-byte) char constant */
pc = c; /* save delimiter */
do /* scan through character constant,
** discarding escape chars
*/
{
while ((c = getnc()) == '\\')
getnc();
} while (c != pc && c != EOF);
break;
}
if (c == EOF)
return 0;
else c = getnc();
}
}
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