怎么有没搞明白，下面的程序，在程序中间定义的变量为什么编译器不报错？
/*
** Written by Dann Corbit as K&R 2, Exercise 4-2 (Page 73).
** Keep in mind that this is *JUST* a student exercise, and is
** light years away from being robust.
**
** Actually, it's kind of embarassing, but I'm too lazy to fix it.
**
** Caveat Emptor, not my fault if demons fly out of your nose,
** and all of that.
*/
#include
#include
#include
#include
#include
int my_atof(char *string, double *pnumber)
{
/* Convert char string to double data type. */
double retval;
double one_tenth = 0.1;
double ten = 10.0;
double zero = 0.0;
int found_digits = 0;
int is_negative = 0;
char *num;
/* Check pointers. */
if (pnumber == 0) {
return 0;
}
if (string == 0) {
*pnumber = zero;
return 0;
}
retval = zero;
num = string;
/* Advance past white space. */
while (isspace(*num))
num++;
/* Check for sign. */
if (*num == '+')
num++;
else if (*num == '-') {
is_negative = 1;
num++;
}
/* Calculate the integer part. */
while (isdigit(*num)) {
found_digits = 1;
retval *= ten;
retval += *num - '0';
num++;
}
/* Calculate the fractional part. */
if (*num == '.') {
double scale = one_tenth;
num++;
while (isdigit(*num)) {
found_digits = 1;
retval += scale * (*num - '0');
num++;
scale *= one_tenth;
}
}
/* If this is not a number, return error condition. */
if (!found_digits) {
*pnumber = zero;
return 0;
}
/* If all digits of integer & fractional part are 0, return 0.0 */
if (retval == zero) {
*pnumber = zero;
return 1; /* Not an error condition, and no need to
* continue. */
}
/* Process the exponent (if any) */
if ((*num == 'e') || (*num == 'E')) {
int neg_exponent = 0;
int get_out = 0;
long index;
long exponent = 0;
double getting_too_big = DBL_MAX * one_tenth;
double getting_too_small = DBL_MIN * ten;
num++;
if (*num == '+')
num++;
else if (*num == '-') {
num++;
neg_exponent = 1;
}
/* What if the exponent is empty? Return the current result. */
if (!isdigit(*num)) {
if (is_negative)
retval = -retval;
*pnumber = retval;
return (1);
}
/* Convert char exponent to number <= 2 billion. */
while (isdigit(*num) && (exponent < LONG_MAX / 10)) {
exponent *= 10;
exponent += *num - '0';
num++;
}
/* Compensate for the exponent. */
if (neg_exponent) {
for (index = 1; index <= exponent && !get_out; index++)
if (retval < getting_too_small) {
get_out = 1;
retval = DBL_MIN;
} else
retval *= one_tenth;
} else
for (index = 1; index <= exponent && !get_out; index++) {
if (retval > getting_too_big) {
get_out = 1;
retval = DBL_MAX;
} else
retval *= ten;
}
}
if (is_negative)
retval = -retval;
*pnumber = retval;
return (1);
}
/*
** Lame and evil wrapper function to give the exercise the requested
** interface. Dann Corbit will plead innocent to the end.
** It's very existence means that the code is not conforming.
** Pretend you are a C library implementer, OK? But you would fix
** all those bleeding gaps, I am sure.
*/
double atof(char *s)
{
double d = 0.0;
if (!my_atof(s, &d))
{
#ifdef DEBUG
fputs("Error converting string in [sic] atof()", stderr);
#endif
raise(SIGFPE);
}
return d;
}
char *strings[] = {
"1.0e43",
"999.999",
"123.456e-9",
"-1.2e-3",
"1.2e-3",
"-1.2E3",
"-1.2e0",
"cat",
"",
0
};
int main(void)
{
int i = 0;
for (; *strings[i]; i++)
printf("atof(%s) = %g\n", strings[i], atof(strings[i]));
return 0;
}
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