On Tue, 2007-05-22 at 14:06 -0600, David B Darrough wrote: > Yeah, I was afraid of that...it looks like that is the answer. Of course I > then have to remember to deallocate space for the sub-arrays before > deallocating the main array. But I think you're right.
May I ask why you need to allocate this on the heap? If all you need is the ability to be dynamic, and you know your array won't exceed the stack size, you can use gcc's alloca() allocator to allocate stack memory dynamically. I use alloca extensively when dealing with string operations, for example. You don't ever have to free the memory; just return from the subroutine and it's all cleared off. You obviously cannot return a string as a return value from a parameter that's been alloca'ted. > > Thanks, > Dave > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Michael L Torrie > Sent: Tuesday, May 22, 2007 2:04 PM > To: BYU Unix Users Group > Subject: Re: [uug] Dynamically allocated arrays > > On Tue, 2007-05-22 at 13:34 -0600, David B Darrough wrote: > > I tried that and it works for a single dimension but if you add a second > > dimension, you get an error: non-constant expression as an array bound. > Here > > is what I tried and had fail: > > > > int a = 5; > > int b = 6; > > int *array; > > > > array = new int[a][b]; > > > > ... > > > > It fails at the array = new int[a][b] line because it wants a constant. > Any > > other thoughts? > > The reason it's not working is because you're actually not asking C++ > (or C for that matter) to create a two-dimensional array here. Remember > that arrays in C are really just pointers. The way that the [] works is > by de-referencing pointers (at least in this instance). So what you > asked C for in your code above was an array of integer arrays > (convertible but not equivalent to integer pointers). The type of the > array you asked for was really int[b], which isn't a valid type in C > (it's indeterminate). > > The only way I know of to get dynamically-allocated multi-dimensional > arrays in C is to do allocate one dimension at a time. This is, alas, > not an order N operation: > > array=new (int *)[a]; > for(i=0;i<a;i++) > array[i]=new int[b]; > > > then you can access each element using your traditional [][] notation. > > > > > > - Dave > > > > -----Original Message----- > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > On > > Behalf Of Byron Clark > > Sent: Tuesday, May 22, 2007 1:19 PM > > To: BYU Unix Users Group > > Subject: Re: [uug] Dynamically allocated arrays > > > > On 5/22/07, David B Darrough <[EMAIL PROTECTED]> wrote: > > > My workaround has always been to create a vector, pushing onto the back > of > > > it all of the elements, then creating a function that takes an x and a > y > > > value and indexes into the vector like it is a two dimensional array. > > There > > > has got to be a better way.... I have read something about dynamic > arrays > > > being created on the heap with the new command at runtime but I'm not > sure > > > how to use them. Any thoughts? > > > > Here's how to do the dynamic arrays: > > > > int a = 5; > > int *array; > > > > array = new int[a]; > > // use the array > > array[0] = 4; > > delete [] array; > > > > This link shows one way of doing a multidimensional array on the heap: > > http://www.parashift.com/c++-faq-lite/freestore-mgmt.html#faq-16.16 > > -------------------- > > BYU Unix Users Group > > http://uug.byu.edu/ > > > > The opinions expressed in this message are the responsibility of their > > author. They are not endorsed by BYU, the BYU CS Department or BYU-UUG. > > ___________________________________________________________________ > > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list > > > > > > -------------------- > > BYU Unix Users Group > > http://uug.byu.edu/ > > > > The opinions expressed in this message are the responsibility of their > > author. They are not endorsed by BYU, the BYU CS Department or BYU-UUG. > > ___________________________________________________________________ > > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list > > > > -------------------- > BYU Unix Users Group > http://uug.byu.edu/ > > The opinions expressed in this message are the responsibility of their > author. They are not endorsed by BYU, the BYU CS Department or BYU-UUG. > ___________________________________________________________________ > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list > > > -------------------- > BYU Unix Users Group > http://uug.byu.edu/ > > The opinions expressed in this message are the responsibility of their > author. They are not endorsed by BYU, the BYU CS Department or BYU-UUG. > ___________________________________________________________________ > List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list > -------------------- BYU Unix Users Group http://uug.byu.edu/ The opinions expressed in this message are the responsibility of their author. They are not endorsed by BYU, the BYU CS Department or BYU-UUG. ___________________________________________________________________ List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list
