求Scanf 这个为什么输入0.5会无限循环! - 黑马程序员技术交流社区

int
_doscan(register FILE *stream, const char *format, va_list ap)
{
int done = 0; /* number of items done */
int nrchars = 0; /* number of characters read */
int conv = 0; /* # of conversions */
int base; /* conversion base */
unsigned long val; /* an integer value */
register char *str; /* temporary pointer */
char *tmp_string; /* ditto */
unsigned width = 0; /* width of field */
int flags; /* some flags */
int reverse; /* reverse the checking in [...] */
int kind;
register int ic = EOF; /* the input character */
#ifndef NOFLOAT
long double ld_val;
#endif
if (!*format) return 0;
while (1) {
if (isspace(*format)) {
while (isspace(*format))
format++; /* skip whitespace */
ic = getc(stream);
nrchars++;
while (isspace (ic)) {
ic = getc(stream);
nrchars++;
}
if (ic != EOF) ungetc(ic,stream);
nrchars--;
}
if (!*format) break; /* end of format */
if (*format != '%') {
ic = getc(stream);
nrchars++;
if (ic != *format++) break; /* error */
continue;
}
format++;
if (*format == '%') {
ic = getc(stream);
nrchars++;
if (ic == '%') {
format++;
continue;
}
else break;
}
flags = 0;
if (*format == '*') {
format++;
flags |= FL_NOASSIGN;
}
if (isdigit (*format)) {
flags |= FL_WIDTHSPEC;
for (width = 0; isdigit (*format);)
width = width * 10 + *format++ - '0';
}
switch (*format) {
case 'h': flags |= FL_SHORT; format++; break;
case 'l': flags |= FL_LONG; format++; break;
case 'L': flags |= FL_LONGDOUBLE; format++; break;
}
kind = *format;
if ((kind != 'c') && (kind != '[') && (kind != 'n')) {
do {
ic = getc(stream);
nrchars++;
} while (isspace(ic));
if (ic == EOF) break; /* outer while */
} else if (kind != 'n') { /* %c or %[ */
ic = getc(stream);
if (ic == EOF) break; /* outer while */
nrchars++;
}
switch (kind) {
default:
/* not recognized, like %q */
return conv || (ic != EOF) ? done : EOF;
break;
case 'n':
if (!(flags & FL_NOASSIGN)) { /* silly, though */
if (flags & FL_SHORT)
*va_arg(ap, short *) = (short) nrchars;
else if (flags & FL_LONG)
*va_arg(ap, long *) = (long) nrchars;
else
*va_arg(ap, int *) = (int) nrchars;
}
break;
case 'p': /* pointer */
set_pointer(flags);
/* fallthrough */
case 'b': /* binary */
case 'd': /* decimal */
case 'i': /* general integer */
case 'o': /* octal */
case 'u': /* unsigned */
case 'x': /* hexadecimal */
case 'X': /* ditto */
if (!(flags & FL_WIDTHSPEC) || width > NUMLEN)
width = NUMLEN;
if (!width) return done;
str = o_collect(ic, stream, kind, width, &base);
if (str < inp_buf
|| (str == inp_buf
&& (*str == '-'
|| *str == '+'))) return done;
/*
* Although the length of the number is str-inp_buf+1
* we don't add the 1 since we counted it already
*/
nrchars += str - inp_buf;
if (!(flags & FL_NOASSIGN)) {
if (kind == 'd' || kind == 'i')
val = strtol(inp_buf, &tmp_string, base);
else
val = strtoul(inp_buf, &tmp_string, base);
if (flags & FL_LONG)
*va_arg(ap, unsigned long *) = (unsigned long) val;
else if (flags & FL_SHORT)
*va_arg(ap, unsigned short *) = (unsigned short) val;
else
*va_arg(ap, unsigned *) = (unsigned) val;
}
break;
case 'c':
if (!(flags & FL_WIDTHSPEC))
width = 1;
if (!(flags & FL_NOASSIGN))
str = va_arg(ap, char *);
if (!width) return done;
while (width && ic != EOF) {
if (!(flags & FL_NOASSIGN))
*str++ = (char) ic;
if (--width) {
ic = getc(stream);
nrchars++;
}
}
if (width) {
if (ic != EOF) ungetc(ic,stream);
nrchars--;
}
break;
case 's':
if (!(flags & FL_WIDTHSPEC))
width = 0xffff;
if (!(flags & FL_NOASSIGN))
str = va_arg(ap, char *);
if (!width) return done;
while (width && ic != EOF && !isspace(ic)) {
if (!(flags & FL_NOASSIGN))
*str++ = (char) ic;
if (--width) {
ic = getc(stream);
nrchars++;
}
}
/* terminate the string */
if (!(flags & FL_NOASSIGN))
*str = '\0';
if (width) {
if (ic != EOF) ungetc(ic,stream);
nrchars--;
}
break;
case '[':
if (!(flags & FL_WIDTHSPEC))
width = 0xffff;
if (!width) return done;
if ( *++format == '^' ) {
reverse = 1;
format++;
} else
reverse = 0;
for (str = Xtable; str < &Xtable[NR_CHARS]
; str++)
*str = 0;
if (*format == ']') Xtable[*format++] = 1;
while (*format && *format != ']') {
Xtable[*format++] = 1;
if (*format == '-') {
format++;
if (*format
&& *format != ']'
&& *(format) >= *(format -2)) {
int c;
for( c = *(format -2) + 1
; c <= *format ; c++)
Xtable[c] = 1;
format++;
}
else Xtable['-'] = 1;
}
}
if (!*format) return done;
if (!(Xtable[ic] ^ reverse)) {
/* MAT 8/9/96 no match must return character */
ungetc(ic, stream);
return done;
}
if (!(flags & FL_NOASSIGN))
str = va_arg(ap, char *);
do {
if (!(flags & FL_NOASSIGN))
*str++ = (char) ic;
if (--width) {
ic = getc(stream);
nrchars++;
}
} while (width && ic != EOF && (Xtable[ic] ^ reverse));
if (width) {
if (ic != EOF) ungetc(ic, stream);
nrchars--;
}
if (!(flags & FL_NOASSIGN)) { /* terminate string */
*str = '\0';
}
break;
#ifndef NOFLOAT
case 'e':
case 'E':
case 'f':
case 'g':
case 'G':
if (!(flags & FL_WIDTHSPEC) || width > NUMLEN)
width = NUMLEN;
if (!width) return done;
str = f_collect(ic, stream, width);
if (str < inp_buf
|| (str == inp_buf
&& (*str == '-'
|| *str == '+'))) return done;
/*
* Although the length of the number is str-inp_buf+1
* we don't add the 1 since we counted it already
*/
nrchars += str - inp_buf;
if (!(flags & FL_NOASSIGN)) {
ld_val = strtod(inp_buf, &tmp_string);
if (flags & FL_LONGDOUBLE)
*va_arg(ap, long double *) = (long double) ld_val;
else
if (flags & FL_LONG)
*va_arg(ap, double *) = (double) ld_val;
else
*va_arg(ap, float *) = (float) ld_val;
}
break;
#endif
} /* end switch */
conv++;
if (!(flags & FL_NOASSIGN) && kind != 'n') done++;
format++;
}
return conv || (ic != EOF) ? done : EOF;
}
_doscan函数代码

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