• Dan (2/2) May 17 2009 Structs can't easily be compared in C because of potential 'padding' ins...
• grauzone (2/5) May 17 2009 How about using the == operator?
• Jarrett Billingsley (4/6) May 17 2009 As grauzone said, you just use == to compare them. D solves the issue
• Dan (4/12) May 17 2009 That sounds great, and seems like yet another reason for me to switch to...
• Jarrett Billingsley (4/6) May 17 2009 Sure, you can calloc or memset a C struct. I've never heard of
• Dan (2/10) May 17 2009 Perhaps I'm mistaken there. However, going through about 5-10 results on...
• grauzone (11/13) May 17 2009 I heard that the compiler can change the padding bytes to non-null on

Dan <twinbee42 skytopia.com> writes:

Structs can't easily be compared in C because of potential 'padding' inside the
struct which may (or may not) exist.

I was jut wondering if D somehow gets round this, and allows something like
memcmp to easily compare two structs.

grauzone <none example.net> writes:

Dan wrote:
 Structs can't easily be compared in C because of potential 'padding' inside
the struct which may (or may not) exist.
 
 I was jut wondering if D somehow gets round this, and allows something like
memcmp to easily compare two structs.

How about using the == operator?

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

On Sun, May 17, 2009 at 3:55 PM, Dan <twinbee42 skytopia.com> wrote:
 Structs can't easily be compared in C because of potential 'padding' inside
the struct which may (or may not) exist.

 I was jut wondering if D somehow gets round this, and allows something like
memcmp to easily compare two structs.

As grauzone said, you just use == to compare them.  D solves the issue
with C's uninitialized holes by always initializing structs.
Therefore the padding holes are always filled with 0s.

Dan <twinbee42 skytopia.com> writes:

That sounds great, and seems like yet another reason for me to switch to D
(other than the removal of header files which always seemed like a kludge).

Just for the record though, I think one can initialize/blank/calloc C structs
too, but the problem is that some struct elements (of the same array) may have
padding while others don't, or perhaps they have different size paddings.

Dan


Jarrett Billingsley Wrote:

 On Sun, May 17, 2009 at 3:55 PM, Dan <twinbee42 skytopia.com> wrote:
 Structs can't easily be compared in C because of potential 'padding' inside
the struct which may (or may not) exist.

 I was jut wondering if D somehow gets round this, and allows something like
memcmp to easily compare two structs.

 
 As grauzone said, you just use == to compare them.  D solves the issue
 with C's uninitialized holes by always initializing structs.
 Therefore the padding holes are always filled with 0s.

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

On Sun, May 17, 2009 at 5:00 PM, Dan <twinbee42 skytopia.com> wrote:
 That sounds great, and seems like yet another reason for me to switch to D
(other than the removal of header files which always seemed like a kludge).

 Just for the record though, I think one can initialize/blank/calloc C structs
too, but the problem is that some struct elements (of the same array) may have
padding while others don't, or perhaps they have different size paddings.

Sure, you can calloc or memset a C struct.  I've never heard of
padding varying for different instances of the same struct type, but
who knows.  So much of C is implementation-defined..

Dan <twinbee42 skytopia.com> writes:

Jarrett Billingsley Wrote:

 On Sun, May 17, 2009 at 5:00 PM, Dan <twinbee42 skytopia.com> wrote:
 That sounds great, and seems like yet another reason for me to switch to D
(other than the removal of header files which always seemed like a kludge).

 Just for the record though, I think one can initialize/blank/calloc C structs
too, but the problem is that some struct elements (of the same array) may have
padding while others don't, or perhaps they have different size paddings.

 
 Sure, you can calloc or memset a C struct.  I've never heard of
 padding varying for different instances of the same struct type, but
 who knows.  So much of C is implementation-defined..

Perhaps I'm mistaken there. However, going through about 5-10 results on
Google, it would seem there's no real solution in C to compare structs of the
same type, because of whatever issues the padding thing may do. If it was as
simple as memset/calloc, I'm sure that would've been mentioned.

grauzone <none example.net> writes:

Dan wrote:
 That sounds great, and seems like yet another reason for me to switch to D
(other than the removal of header files which always seemed like a kludge).

I heard that the compiler can change the padding bytes to non-null on 
some occasions. For example, the compiler could treat member a as 32 bit 
value when assigning it:

struct {
    char a; //offset 0
    int b;  //offset 4
}

Nothing in the C standard says that the compiler has to preserve the 
padding bytes between a and b. So I was told.

 Just for the record though, I think one can initialize/blank/calloc C structs
too, but the problem is that some struct elements (of the same array) may have
padding while others don't, or perhaps they have different size paddings.

Not sure what you mean.