manohar@csl.dl.nec.com (Mun o her) (05/14/91)
How to get the functionality of 'realloc()' in C++ ?
Note : realloc() is used to change the size of the memory.
The problem I have is as follows :-
/** a part of prog */
int i=0, data_func();
int *pt = new int[50];
while(1){
pt[i++] = data_func();
<.... whenever the the array is filled up .... I want the array to double in
size. this is done using realloc() in C programs... realloc(pt,100) >
}
Pardon me if this question is too trivial !
--
My Life is like a boat in a dry river. I didnot want to drag the boat out, I
wanted to give it a river.
----Boris Pasternak's(of Dr. Zhivago's fame) letter to Mayor Kowaski
Manohar S. Gudavalli ||Internet: manohar@csl.dl.nec.comcadsi@ccad.uiowa.edu (CADSI) (05/14/91)
From article <1991May13.191807.29295@csl.dl.nec.com>, by manohar@csl.dl.nec.com (Mun o her): > How to get the functionality of 'realloc()' in C++ ? > Note : realloc() is used to change the size of the memory. > > The problem I have is as follows :- > > /** a part of prog */ > int i=0, data_func(); > > int *pt = new int[50]; > while(1){ > pt[i++] = data_func(); > <.... whenever the the array is filled up .... I want the array to double in > size. this is done using realloc() in C programs... realloc(pt,100) > > > } > Seems to me an Array class would be helpful here. Just overload the [] operator to reallocate the vector as necessary. malloc and realloc will work fine in C++. In addition, if you wanna use the new operator, you could allocate the new vector, copy the old into it, then delete the first. Otherwise, overload the new operator for the Array class to be smart about the re-allocation. |----------------------------------------------------------------------------| |Tom Hite | The views expressed by me | |Manager, Product development | are mine, not necessarily | |CADSI (Computer Aided Design Software Inc. | the views of CADSI. | |----------------------------------------------------------------------------|
steve@taumet.com (Stephen Clamage) (05/15/91)
manohar@csl.dl.nec.com (Mun o her) writes: >How to get the functionality of 'realloc()' in C++ ? >Note : realloc() is used to change the size of the memory. C++ does not support the functionality of realloc() via 'new' and 'delete'. You have two choices: 1. Do it by hand. Use 'new' to acquire a larger space, copy the data, and 'delete' the old space. This is what realloc() does anyway, if the space cannot be extended where it is. 2. Use malloc(), realloc(), and free() in your C++ program. Check your documentation to see whether this is supported. It probably is. WARNINGS: Do not use malloc/realloc for objects with constructors. Do not 'delete' something allocated with malloc/realloc. Do not 'free' something allocated with 'new'. -- Steve Clamage, TauMetric Corp, steve@taumet.com
roger@zuken.co.jp (Roger Meunier) (05/17/91)
In article <728@taumet.com> steve@taumet.com (Stephen Clamage) writes: > WARNINGS: Do not use malloc/realloc for objects with > constructors. Do not 'delete' something allocated with > malloc/realloc. Do not 'free' something allocated with 'new'. How is strdup() implemented in a C++ environment? Does it allocate using 'new" or malloc()? -- Roger Meunier @ Zuken, Inc. Yokohama, Japan (roger@zuken.co.jp)
steve@taumet.com (Stephen Clamage) (05/17/91)
roger@zuken.co.jp (Roger Meunier) writes: >In article <728@taumet.com> steve@taumet.com (Stephen Clamage) writes: > > WARNINGS: Do not use malloc/realloc for objects with > > constructors. Do not 'delete' something allocated with > > malloc/realloc. Do not 'free' something allocated with 'new'. >How is strdup() implemented in a C++ environment? Does it allocate >using 'new" or malloc()? The warnings were intended as rules for happy living. If you follow them, you are less likely to get into trouble. As to strdup(), it is not an standard ANSI C function, and as yet there is no standard C++ library. Not all systems have a strdup(). If it exists, it is most likely to be from the C library, and hence written in C. In that case, it would be likely to use malloc(), but who knows? It might use its own private memory scheme, like grabbing a chunk of memory with sbrk() and handing out pieces. You have a few choices: 1. Be a wimp. Don't try to recover the memory allocated to these strings. 2. Be safe. Write your own strdup -- it is a very tiny function. Use 'new' or 'malloc' as the fancy strikes you. 3. Play the odds. It is unlikely that strdup uses 'new', so just use 'free' to recover storage. 4. Throw caution to the winds, and use 'delete'. It is likely that 'new' and 'delete' just use the system 'malloc' and 'free' anyway. 5. Hack! Disassemble the library strdup to see what it calls, then write your code accordingly. Of course, you have to repeat this process for each library or system change. -- Steve Clamage, TauMetric Corp, steve@taumet.com
robertk@lotatg.lotus.com (Robert Krajewski) (05/21/91)
If you are really looking for the functionality of arrays that can be resized, you might as well use realloc() directly, and place the implementation inside an array class. If you are using the array as container (with one class of C++ objects directly residing in the storage managed by the array), you will need to use the placement form of the operator so that your constructors are run properly (in a loop, most likely). If you shrink the array, you will need to manually run the destructors for the deleted objects. Container classes are pretty useful, especially when you want to tune the storage of a particular family or set of objects. For example, you could write an array class that used handle-based storage on the Mac or Windows, and thus be better-behaved than a simple port that assumed optimal implementations of malloc/realloc/free.