Ad:

C++ Discussion Thread
Unsolved
Views: 87155

You are currently viewing page 2 of this multi-page discussion thread; Jump to the first page

Jun 1st, 2005

Re: get length of a dynamic array

>> Just make it this and it will work (i think)
No offense, but when you're guessing, you're not helping. Most of the time a guess is either grievously wrong, or has subtle problems.

>> so stop criticizing people
It's called constructive criticism. If you don't want to learn then don't bother trying to help because you'll just give bad advice. If you think you know everything then don't bother trying to help because you'll probably give bad advice and then turn the thread into a flame war when someone who knows better corrects you.

Dogtree

Reputation Points: 35

Solved Threads: 3

Posting Whiz in Training

Offline

232 posts
since May 2005

Permalink

Jun 3rd, 2005

Re: get length of a dynamic array

I tried using the sizeof operator as suggested above. But everytime for an int array it gives "1" as output and for a char array it gives "4". No matter how many elements I store in the array.
I donot know the usage of std::vector or boost::array. Can someone help? Pls tell me how can I get the number of elements stored in a dynamic array using them?

P.S:I had changed the example to char type as I was not sure if 'String' is a valid data type in C or C++. Is it?

swets_here

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

4 posts
since May 2005

Permalink

Jun 3rd, 2005

Re: get length of a dynamic array

Basically, the only way to do this is what narue suggested and pass in the actual size as a parameter to the function. Either that, or use an STL collection, and use .size()

winbatch

Reputation Points: 68

Solved Threads: 18

Posting Pro in Training

Offline

466 posts
since Feb 2005

Permalink

Jun 3rd, 2005

Re: get length of a dynamic array

>> I tried using the sizeof operator as suggested above.
Don't bother, it won't work.

>> Pls tell me how can I get the number of elements stored in a dynamic array using them?
The only way to get the size of a dynamic array is to save the size when you allocate memory. The only way to get the size of an array parameter is to pass the size as another parameter:

C++ Syntax (Toggle Plain Text)
// Get the size of a dynamic array
char *p = new char[10];
int sz = 10; // Save the size!
// Get the size of a dynamic array
char *p = new char[10];
int sz = 10; // Save the size!

C++ Syntax (Toggle Plain Text)
// Get the size of an array parameter
void foo(char array[], int size); // Pass the size!
// Get the size of an array parameter
void foo(char array[], int size); // Pass the size!

>> I donot know the usage of std::vector or boost::array.
That's not a good excuse.

If you don't know the usage of a feature but you clearly need it, then it's time to learn. It's almost always better to use a container class than it is to use arrays anyway. Arrays are error prone while container classes work hard to protect you from those potential errors.

>> Is it?
String is not, unless you define it yourself, std::string is a class in the standard library.

Dogtree

Reputation Points: 35

Solved Threads: 3

Posting Whiz in Training

Offline

232 posts
since May 2005

Permalink

Dec 25th, 2006

Re: get length of a dynamic array

hi,

i'm studing computer sciences and i just met this problem.
i know it's been a long time the thread has been opened but i have one more question about it.

i already thought of passing the size of the dynamic array in parameter and i'm sure this will work fine, but as i am a studient, i always want to know more about it and even more when something seems wiered to me : if the only way of knowing the size of a dynamic array is by sending its size, how does free works ? you just pass the pointer as parameter and it cleans up the memory... i bet this function has the solution we are looking for.. but unfortunatly i have no books detailed enough to answer my question and i can't find anything on the web neither...

maybe there is a "Mister know-it-all" over here who can help me to understand that.

(i'm sorry if my english isn't verry correct but this is not my first language

and so, please don't make answers to hard to understand, thank you

)

vamp74100

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

1 posts
since Dec 2006

Permalink

Dec 25th, 2006

Re: get length of a dynamic array

Click to Expand / Collapse Quote originally posted by Phaelax ...

Can't seem to figure this out.
C++ Syntax (Toggle Plain Text)
string *array;
 
void addNodes(string names[])
{
	array = names;
	//how many elements in the array???
}
string *array; void addNodes(string names[]) { array = names; //how many elements in the array??? }

std::string has a function size() that will tell the current size.

C++ Syntax (Toggle Plain Text)
void addNodes(string names[])
{
	cout << "size of array is " << names.size() << "\n";
}
void addNodes(string names[])
{
	cout << "size of array is " << names.size() << "\n";
}

>> array = names;
That does not work because you variable names is a c++ class, not a pointer. If you want the pointer, then use c_str()

C++ Syntax (Toggle Plain Text)
const char* array = names.c_str();
const char* array = names.c_str();

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2282

Retired and Enjoying Life

Offline

21,949 posts
since Aug 2005

Permalink

Dec 25th, 2006

Re: get length of a dynamic array

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

std::string has a function size() that will tell the current size.
C++ Syntax (Toggle Plain Text)
void addNodes(string names[])
{
    cout << "size of array is " << names.size() << "\n";
}
void addNodes(string names[]) { cout << "size of array is " << names.size() << "\n"; }

Hmm...you are forgetting that names is an array of strings and not a std::string or a vector. So you can't apply the size( ) function to it, it is applicable to C++ containers, not array of containers. The only way to do this thing correctly is to do it like specified by Miss Narue in the second post.

~s.o.s~

Super Moderator

Featured Poster

Reputation Points: 3233

Solved Threads: 719

Failure as a human

Offline

8,871 posts
since Jun 2006

Permalink

Dec 25th, 2006

Re: get length of a dynamic array

Click to Expand / Collapse Quote originally posted by ~s.o.s~ ...

Hmm...you are forgetting that names is an array of strings and not a std::string or a vector. So you can't apply the size( ) function to it, it is applicable to C++ containers, not array of containers. The only way to do this thing correctly is to do it like specified by Miss Narue in the second post.

Yes you are correct -- my mistake. Best thing for the op to do is use a vector instead of an array. I was wondering at the time how Narue could possibly make such a mistake -- turns out she didn't.

Last edited by Ancient Dragon; Dec 25th, 2006 at 8:59 pm.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2282

Retired and Enjoying Life

Offline

21,949 posts
since Aug 2005

Permalink

Sep 13th, 2008

You can find the size of a dynamic array

I'm not an expert, but I was reading this article:
http://www.icce.rug.nl/docs/cplusplu...us09.html#l153

Apparently, if you overloaded the operator delete like this:
void operator delete[](void *p, size_t size);

the parameter "size" will tell you how long the array is.

However, if you want the normal delete[], you'll have to write "::delete[]"

s0me1

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

3 posts
since Sep 2008

Permalink

Sep 13th, 2008

Re: You can find the size of a dynamic array

Click to Expand / Collapse Quote originally posted by s0me1 ...

I'm not an expert, but I was reading this article:
http://www.icce.rug.nl/docs/cplusplu...us09.html#l153

Apparently, if you overloaded the operator delete like this:
void operator delete[](void *p, size_t size);

the parameter "size" will tell you how long the array is.

However, if you want the normal delete[], you'll have to write "::delete[]"

Curiously, the C++ standard does not actually specify what value is passed as the size_t argument. In practice, it would be reasonable to expect (hope?) it would have the value passed to the corresponding invocation of operator new[](). If so, it would have to be divided by sizeof(the_type) to get the number of elements.

Since the destructors of all elements of the array will have been invoked before operator delete[]() is actually called, there is not much that can be done with the size_t argument other than pass it to a deallocation function (eg ::operator delete[]()) or print out the number of elements that were in the array being deallocated. The elements themselves will no longer exist, so no operation on them is allowed.

grumpier

Reputation Points: 193

Solved Threads: 32

Posting Whiz in Training

Offline

206 posts
since Aug 2008

Previous
1
Page 2
3
4
Next

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: inheritance public , private difference

Next Thread in C++ Forum Timeline: How do you have a variable name itself?

DaniWeb Message

Cancel Changes

User Name
Password