how to create structure array with dynamic size

Question

I want to create a structure of array dynamically but i dont know the exact size so it will be added whenever i want...

Consider the following example..

 Struct abc
 {
    double **ptrPoints;
    int size;    
  };

i am defining pointer variable

abc* obj;

i dont know the exact size will be so i can not defile like

obj = new abc[size];

the elements will be added whenever condition satisfied.. i want it like vector but i dont want to use it ....

Please suggest me any way to write the functionality like this... Thank u

*"i want it like vector but i dont want to use it"* Why exactly? — Nawaz, Aug 09 '13 at 05:52
Use `std::vector`, even if you don't want to use it. Or give a good reason for not wanting it. — juanchopanza, Aug 09 '13 at 05:53
Read; learn: http://blogs.msdn.com/b/oldnewthing/archive/2013/02/06/10391383.aspx — chris, Aug 09 '13 at 05:54
how are you using the vector? if it's causing memory leaks something's wrong. — dutt, Aug 09 '13 at 05:55
@Jitendra, I laughed aloud. You must be doing something inherently wrong if that's the case. It's not the fault of the vector. — chris, Aug 09 '13 at 05:55
@Jitendra: vector causes memory leaks? you mean the guy who designed vector didn't know enough? — Nawaz, Aug 09 '13 at 05:56
i am not saying this actualy i have one 2d array within the structure i cant delete it after pushing into vector so i create copy constructor then to i face memory leak issue so i thought the problem will solve if i array instead of vector — Jitendra, Aug 09 '13 at 06:00
@Jitendra, Again, change the pointers to something that manages its own memory. It's trivial to make a small `Matrix` class if a multidimensional vector won't work for you. And when you said a 2D array, I thought you meant that. You mean you have a pointer to a pointer that acts like a 2D array. — chris, Aug 09 '13 at 06:02
Search for info "shared_ptr" and use it, memory management becomes a lot easier. — dutt, Aug 09 '13 at 06:04
@Jitendra, The most straightforward thing to do would be to do `std::vector> points;`, assuming that is, indeed, used as a jagged array. — chris, Aug 09 '13 at 06:04
@chris thanks i will check this pls share if u have any link regarding this — Jitendra, Aug 09 '13 at 06:05
@Jitendra, [This answer](http://stackoverflow.com/questions/2216017/dynamical-two-dimension-array-according-to-input/2216055#2216055) is a relevant and good read as well. — chris, Aug 09 '13 at 06:19
+1 to dutt for asking how he's using the vector that's causing memory leaks instead of laughing at the asker's contention. — Prime, Aug 09 '13 at 06:27

score 2 · Answer 1 · answered Aug 09 '13 at 05:55

2

Look up vector. Does all the leg work for you.

answered Aug 09 '13 at 05:55

Ed Heal

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score 0 · Answer 2 · answered Aug 09 '13 at 05:58

0

Wonder why you do not want to use vector. But you may initially declare array of sufficient size. Then maintain a counter of the elements being used up. If it has no space then use realloc.

Seems the only solution except vectors.

See THIS for realloc

answered Aug 09 '13 at 05:58

Saksham

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Please do not use `malloc/realloc/..` for C++. C++ uses new and perhaps has different house keeping rules. – Ed Heal Aug 09 '13 at 06:00
@EdHeal can I get an idea how to replace `realloc` with `new[]` and `delete[]` – Saksham Aug 09 '13 at 06:03
1

@Saksham, There's placement new for that purpose. Of course using either is not usually in your best interest. – chris Aug 09 '13 at 06:06

how to create structure array with dynamic size

2 Answers2