Hi,
please look at the following code:
//
#include <stdio.h>
#include <stdlib.h>
//
#include <stdio.h>
#include <stdlib.h>
//
int main(void)
{
char *szValue = "-i";
char *p = NULL;
double a = strtod(szValue, &p);
// check for error
if ( *p && p )
{
printf("unable to convert %s\n", szValue);
return -1;
}
printf("%s converted is %g\n", szValue, a);
return 0;
}
Compiling and running with POCC.EXE: Version 5.00.13, reports that
Quote"-i converted is 0"
Why ?
Has -i special meaning ?
Or for -i ( or -n, -I and -N ) error is not raised ?
Thank you.
Quote from: Alessio on July 01, 2009, 12:13:00 PM
Quote"-i converted is 0"
Why ?
Has -i special meaning ?
Or for -i ( or -n, -I and -N ) error is not raised ?
"-i" is not real a number or a floating point number. When you look into the help file you can find for
strtod:
Returns:
The converted value, if any.
If no conversion could be performed, zero is returned.
I think this is not a correct answer.
Have you tried to use -z instead of -i ?
Why for -i or -n error is not raised ?
Try this:
//
#include <stdio.h>
#include <stdlib.h>
//
int main(void)
{
int i = 0 ;
char szValue[] = "-a";
char *p = NULL;
double a = 0.0;
for ( i = 'a'; i <= 'z'; i++ )
{
a = strtod(szValue, &p);
// check for error
if ( p && *p )
{
printf("unable to convert %s\n", szValue);
}
else
{
printf("%s converted is %g\n", szValue, a);
}
++szValue[1];
}
return 0;
}
you should get this:
Quoteunable to convert -a
unable to convert -b
unable to convert -c
unable to convert -d
unable to convert -e
unable to convert -f
unable to convert -g
unable to convert -h
-i converted is 0
unable to convert -j
unable to convert -k
unable to convert -l
unable to convert -m
-n converted is 0
unable to convert -o
unable to convert -p
unable to convert -q
unable to convert -r
unable to convert -s
unable to convert -t
unable to convert -u
unable to convert -v
unable to convert -w
unable to convert -x
unable to convert -y
unable to convert -z
strtod sucks
#include <stdio.h>
int main(void)
{
char str[3] = {'-'};
for(int i = 'a'; i <= 'z'; i++)
{
str[1] = i;
double a = 0.0;
int const ret = sscanf(str, "%lg", &a);
printf("%c :", i);
if(ret == 1)
{
printf("conversion OK : a = %g\n", a);
}
else
{
puts("conversion KO");
}
}
return 0;
}Quotea :conversion KO
b :conversion KO
c :conversion KO
d :conversion KO
e :conversion KO
f :conversion KO
g :conversion KO
h :conversion KO
i :conversion KO
j :conversion KO
k :conversion KO
l :conversion KO
m :conversion KO
n :conversion KO
o :conversion KO
p :conversion KO
q :conversion KO
r :conversion KO
s :conversion KO
t :conversion KO
u :conversion KO
v :conversion KO
w :conversion KO
x :conversion KO
y :conversion KO
z :conversion KO
Press any key to continue...
thank you for an alternative to strtod, should this behaviour be considered a bug ?
Quote from: Alessio on July 01, 2009, 04:54:03 PM
thank you for an alternative to strtod, should this behaviour be considered a bug ?
absolutely!
Quote3 The expected form of the subject sequence is an optional plus or minus sign, then one of
the following:
—a nonempty sequence of decimal digits optionally containing a decimal-point
character,then an optional exponent part as defined in 6.4.4.2;
—a 0x or 0X,then a nonempty sequence of hexadecimal digits optionally containing a
decimal-point character,then an optional binary exponent part as defined in 6.4.4.2;
— INF or INFINITY,ignoring case
— NAN or NAN(n-char-sequenceopt),ignoring case in the NAN part, where:
n-char-sequence:
digit
nondigit
n-char-sequence digit
n-char-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input string,
starting with the first non-white-space character,that is of the expected form. The subject
sequence contains no characters if the input string is not of the expected form.
Quote7 If the subject sequence is empty or does not have the expected form, no conversion is
performed; the value of nptr is stored in the object pointed to by endptr,provided
that endptr is not a null pointer.
Quote10 The functions return the converted value, if any. If no conversion could be performed,
zero is returned.
test program:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char str[3] = {'-'};
for(int i = 'a'; i <= 'z'; i++)
{
str[1] = i;
char * endptr = NULL;
double a = strtod(str, &endptr);
printf("%c : ", i);
if((int)a == 0 && endptr == str)
{
puts("Good implementation");
}
else
{
puts("Bad implementation");
}
}
return 0;
}
I guess that the incorrect behaviour for character 'i' and 'n' is a mishandling for special value like INF (or INFINITY) et NAN.
Quote from: Alessio on July 01, 2009, 03:58:12 PM
I think this is not a correct answer.
Have you tried to use -z instead of -i ?
Why for -i or -n error is not raised ?
I am not sure, if the answer is not correct. The strings like "-a" ... "-z" ,exept -"i" and "-n", are converted to -0. "-i" and "-n" are converted to 0. Why not -0, I don't know (perhaps my first answer).
Your way to check for an error is not so good. The pointer p gives you the position how far the string was read. If there a "a", "b" or something else strtod() knows that there is not a number. In the case of 'i' or 'n' there could come a string like "inf", "infinity" or "nan". Try strings like "inx", "nam" or something else and look at the pointer p. So in the case of "-i" and "-n" the hole strings is read and the string behind the pointer p is empty and you think the conversion of the string is correct.
If this behavior is correct, i don't know.
Quote from: AlexN on July 02, 2009, 08:13:21 AM
If this behavior is correct, i don't know.
I give you above what the C99 standard says about conversion. This behaviour is not correct.