Allocating array of pointers to structs

[dev_15]

Hi, I'm going through some code and thought that this allocates an
array of structs but its supposed according to comments to allocate an
array of pointer to structs. What does it actually do

ptrLogArray = new structDisplayLo gData *[iCount];

// iCount = 50 structDisplayLo gData is a strcuture of data

Thanks

[Ben Bacarisse]

dev_15 <na************ @googlemail.com writes:

Hi, I'm going through some code and thought that this allocates an
array of structs but its supposed according to comments to allocate an
array of pointer to structs. What does it actually do

ptrLogArray = new structDisplayLo gData *[iCount];

It behaves as per the comments. What follows 'new' is, syntactically,
a declaration with the name missed out. If you declared this array
you'd write:

structDisplayLo gData *an_array_of_pt rs_to_structs[iCount];

now just remove the name and add 'new':

new structDisplayLo gData *[iCount];

If you thought

structDisplayLo gData *array[iCount];

should mean:

structDisplayLo gData (*array)[iCount];

(i.e. a pointer to an array of structs) rather than what it *does* mean:

structDisplayLo gData *(array[iCount]);

(an array of pointers) then you need to study the syntax a bit more.

--
Ben.

[dev_15]

Thanks also in the code later on is

ptrLogArray[0] = new structDisplayLo gData;

-------------
more code

delete [] ptrLogArray;

Does this delete the structs that the pointers are pointing to?

Ben Bacarisse wrote:

dev_15 <na************ @googlemail.com writes:

Hi, I'm going through some code and thought that this allocates an
array of structs but its supposed according to comments to allocate an
array of pointer to structs. What does it actually do

ptrLogArray = new structDisplayLo gData *[iCount];

It behaves as per the comments. What follows 'new' is, syntactically,
a declaration with the name missed out. If you declared this array
you'd write:

structDisplayLo gData *an_array_of_pt rs_to_structs[iCount];

now just remove the name and add 'new':

new structDisplayLo gData *[iCount];

If you thought

structDisplayLo gData *array[iCount];

should mean:

structDisplayLo gData (*array)[iCount];

(i.e. a pointer to an array of structs) rather than what it *does* mean:

structDisplayLo gData *(array[iCount]);

(an array of pointers) then you need to study the syntax a bit more.

--
Ben.

[David Harmon]

On Thu, 15 Nov 2007 08:45:56 -0800 (PST) in comp.lang.c++, dev_15
<na************ @googlemail.com wrote,

>Hi, I'm going through some code and thought that this allocates an
array of structs but its supposed according to comments to allocate an
array of pointer to structs. What does it actually do

ptrLogArray = new structDisplayLo gData *[iCount];

Array of pointers; that's what the '*' is about.

However, that's probably undesirable code. What happens next is either
trying to write via an uninitialized pointer, or else lots of memory
management headaches. What you wanted instead is probably

std::vector<str uctDisplayLogDa taLogArray(iCou nt);

[Ben Bacarisse]

dev_15 <na************ @googlemail.com writes:

Thanks also in the code later on is

ptrLogArray[0] = new structDisplayLo gData;

-------------
more code

delete [] ptrLogArray;

Does this delete the structs that the pointers are pointing to?

No. As someone else has pointed out, if you are changing the code
consider switching to std::vector.

PS. Don't top post.

--
Ben.

[Default User]

dev_15 wrote:

Thanks also in the code later on is

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.c om/c++-faq-lite/how-to-post.html>