Trouble with references and sscanf.

[aj]

Can someone explain why this example works:

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
int b1, b2, b3, b4;
unsigned char c;
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", &b1, &b2, &b3, &b4,
&c) != 4)
{
return false;
}
if ((b1 | b2 | b3 | b4) 255)
{
return false;
}
if (strspn(ipIpAddress, "0123456789.") < strlen(ipIpAddress))
{
return false;
}
opOct1 = b1;
opOct2 = b2;
opOct3 = b3;
opOct4 = b4;
return true;

}
but this one does not? (Segmentation Fault)

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
unsigned char c;
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", opOct1, opOct2,
opOct3, opOct4, &c) != 4)
{
return false;
}
if ((b1 | b2 | b3 | b4) 255)
{
return false;
}
if (strspn(ipIpAddress, "0123456789.") < strlen(ipIpAddress))
{
return false;
}
return true;

}
In each case, I am passing references to int's to the sscanf
function.

Thanks,
AJ

[Robert Bauck Hamar]

aj wrote:

Can someone explain why this example works:

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
int b1, b2, b3, b4;
unsigned char c;
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", &b1, &b2, &b3, &b4,
&c) != 4)

OK. sscanf expects pointers.

[...]

but this one does not? (Segmentation Fault)

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
unsigned char c;
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", opOct1, opOct2,
opOct3, opOct4, &c) != 4)

Error: sscanf expects pointers, but opOctN are ints. This should be:
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", &opOct1, &opOct2, &opOct3,
&opOct4, &c) != 4)

In each case, I am passing references to int's to the sscanf
function.

In some situations, pointers are called references. But in C++, pointers and
references are distinct creatures. In C++ a reference is an alias of
another object, and once initialised, it behaves exactly as if it is the
referenced object. As you can see, if you need a pointer, you can take the
address of the reference variable.

--
rbh

[aj]

Thanks Robert. You are very correct. I figured the compiler would
recognize that I was passing references (pointers) to the function,
but it was not. It seems unusual that I need to get the pointer of a
reference, when I figured the original reference would do, but I will
live with it :)

Thanks,
AJ

On Jun 25, 3:00 pm, Robert Bauck Hamar <[e-mail]>
wrote:

aj wrote:

Can someone explain why this example works:

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
int b1, b2, b3, b4;
unsigned char c;

if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", &b1, &b2, &b3, &b4,
&c) != 4)

OK. sscanf expects pointers.

[...]

but this one does not? (Segmentation Fault)

bool SomeFunction(const char * ipIpAddress, int &opOct1, int &opOct2,
int &opOct3, int
&opOct4)
{
unsigned char c;

if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", opOct1, opOct2,
opOct3, opOct4, &c) != 4)

Error: sscanf expects pointers, but opOctN are ints. This should be:
if (sscanf(ipIpAddress, "%3i.%3i.%3i.%3i%c", &opOct1, &opOct2, &opOct3,
&opOct4, &c) != 4)

In each case, I am passing references to int's to the sscanf
function.

In some situations, pointers are called references. But in C++, pointers and
references are distinct creatures. In C++ a reference is an alias of
another object, and once initialised, it behaves exactly as if it is the
referenced object. As you can see, if you need a pointer, you can take the
address of the reference variable.

--
rbh

[Default User]

aj wrote:

Thanks Robert.

Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or the group FAQ list:
<http://www.parashift.com/c++-faq-lite/how-to-post.html>

[red floyd]

aj wrote:

1. Do not top post.

Thanks Robert. You are very correct. I figured the compiler would
recognize that I was passing references (pointers) to the function,
but it was not. It seems unusual that I need to get the pointer of a
reference, when I figured the original reference would do,

2. Repeat after me. A reference is *NOT* a pointer. A reference is
*NOT* a pointer.

An implementation may choose to implement them as such, but that is
irrelevant.