Thread: dynamic-variable-sized array

If you were using realloc, instead of malloc, then that would be a good start.

When you do

Code:

_esup1 = malloc((sizeof(int)*(_istor));

then the one thing you most assuredly do not have is

Code:

_esup1[_istor]

If you ask for _istor elements (with malloc), then you get _istor elements, so trying to access the _istor+1'th element (with _esup1[_istor]) is not going to work very well.

You should check the result of malloc, if it's not a null pointer, then the allocation is correct and the runtime error (segv I assume) is due to an incorrect memory access, which is another problem.

Hi there Elysia,

Originally Posted by Elysia

You are using malloc twice, not malloc and realloc... Mistake?
This, in turn, causes memory leaks.

I actually obtain the same error in executaion either by using malloc again inside the loop or realloc.

Or better said, I do not get an error of memory allocation (sorry about that if I wrote that earlier), I do not get to fill the array at every loop step with the correct assignment of element values.

At every loop step I am supposed to add a new element to the array, and assign it the value "_elem", but this does not happen

Thank you again
S.M.

Thank you again,

Originally Posted by Elysia

Few comments.

about your comments, I agree but consider that the code I put is missing a whole part above where I allocate those variables that do not appear allocated in here (just for the sake of shortness in the thread); so, speakign fo that, the allocation of every other variable was done.

Now though, I changed the malloc() inside the loop with the realloc as follows:

Code:

	
for(_ielem=array_numb; _ielem<=nelem-1+array_numb; _ielem++){
		for(_inode=array_numb; _inode<=max_nnode-1+array_numb; _inode++){
		//Update storage counter, storing in _esup1:
			_ipoin = CONN[_ielem][_inode];
			_istor = _esup2[_ipoin-1] + 1;
			_esup2[_ipoin-1] = _istor;
			
			_esup1 = realloc(_esup1, (sizeof(int))*(_istor));

			printf("_istor %d\t size(ESUP1) %d\n",_istor, sizeof(_esup1));
			_esup1[_istor] = _ielem;

but I obtaine a memory allocation error now:

Code:

*** glibc detected *** ./testing.exe: realloc(): invalid next size: 0x175004a8 ***
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6[0xb7c89803]
/lib/tls/i686/cmov/libc.so.6(realloc+0x10b)[0xb7c8b75b]
./testing.exe[0x8049195]
./testing.exe[0x80488c7]
/lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe0)[0xb7c32450]
./testing.exe[0x8048771]
======= Memory map: ========
08048000-0804b000 r-xp 00000000 08:02 516097     /home/simone/Documents/scientific/CFD/myCFD_library/testing_myCFDlibrary/testing.exe
0804b000-0804c000 rw-p 00002000 08:02 516097     /home/simone/Documents/scientific/CFD/myCFD_library/testing_myCFDlibrary/testing.exe
0804c000-0806d000 rw-p 0804c000 00:00 0          [heap]
17500000-17521000 rw-p 17500000 00:00 0 
17521000-17600000 ---p 17521000 00:00 0 
1764c000-b7bf7000 rw-p 1764c000 00:00 0 
b7bf7000-b7c1a000 r-xp 00000000 08:02 2293788    /lib/tls/i686/cmov/libm-2.7.so
b7c1a000-b7c1c000 rw-p 00023000 08:02 2293788    /lib/tls/i686/cmov/libm-2.7.so
b7c1c000-b7d65000 r-xp 00000000 08:02 2293784    /lib/tls/i686/cmov/libc-2.7.so
b7d65000-b7d66000 r--p 00149000 08:02 2293784    /lib/tls/i686/cmov/libc-2.7.so
b7d66000-b7d68000 rw-p 0014a000 08:02 2293784    /lib/tls/i686/cmov/libc-2.7.so
b7d68000-b7d6c000 rw-p b7d68000 00:00 0 
b7d6c000-b7d9c000 r-xp 00000000 08:02 681117     /usr/local/lib/libgslcblas.so.0.0.0
b7d9c000-b7d9d000 rw-p 0002f000 08:02 681117     /usr/local/lib/libgslcblas.so.0.0.0
b7d9d000-b7f1c000 r-xp 00000000 08:02 681124     /usr/local/lib/libgsl.so.0.10.0
b7f1c000-b7f26000 rw-p 0017f000 08:02 681124     /usr/local/lib/libgsl.so.0.10.0
b7f2e000-b7f38000 r-xp 00000000 08:02 2294001    /lib/libgcc_s.so.1
b7f38000-b7f39000 rw-p 0000a000 08:02 2294001    /lib/libgcc_s.so.1
b7f39000-b7f3c000 rw-p b7f39000 00:00 0 
b7f3c000-b7f3d000 r-xp b7f3c000 00:00 0          [vdso]
b7f3d000-b7f57000 r-xp 00000000 08:02 2295295    /lib/ld-2.7.so
b7f57000-b7f59000 rw-p 00019000 08:02 2295295    /lib/ld-2.7.so
bff85000-bff9a000 rw-p bffeb000 00:00 0          [stack]
Aborted

thank you again for all the help and patience!

Code:

for(_ielem=array_numb; _ielem<=nelem-1+array_numb; _ielem++){
		for(_inode=array_numb; _inode<=max_nnode-1+array_numb; _inode++){
		//Update storage counter, storing in _esup1:
			_ipoin = CONN[_ielem][_inode];
			_istor = _esup2[_ipoin-1] + 1; //?
			_esup2[_ipoin-1] = _istor; //?
			
			_esup1 = realloc(_esup1, (sizeof(int))*(_istor));

			printf("_istor %d\t size(ESUP1) %d\n",_istor, sizeof(_esup1));
			_esup1[_istor] = _ielem;  //BOOOM!

So (1) Why realloc one more every time (I think that's what the two lines labeled //? are supposed to do, but it's not quite clear where the numbers are coming from), and (2) the line labeled //BOOOM! is still a really really really really big error.

Originally Posted by Elysia

Then, if you please, can you post the smallest possible sample that demonstrates the problem? I have a hard time sorting through all of the variables and what they do, as well as what values they contain.

Sorry about that, sure, here a more readable version of the code with the correct allocation of the used variables; I hope this helps

Code:

       int *_esup1;
	int *_esup2;
       int _szesup1;
        int CONN[][3] = {{1,2,6},{2,7,6},{2,3,7},{3,8,7},{3,4,8},{4,9,8},{4,5,9},{5,10,9},{7,8,13},{8,12,13},{8,9,12},{9,11,12},{9,10,11}};

       //Allocate _esup2:
	_esup2 = (int*) malloc((sizeof(int[nnode+1])));

       //First allocation of _esup1:
        _szesup1 = 1;
	_esup1 = malloc((sizeof(int))*(_szesup1); 
	
       //Store the elements in _esup1:
	for(_ielem=0; _ielem<=12; _ielem++){
		for(_inode=0; _inode<=2; _inode++){
		//Update storage counter, storing in _esup1:
			_ipoin = CONN[_ielem][_inode];

			_istor = _esup2[_ipoin-1] + 1;

			_esup2[_ipoin-1] = _istor;
			
			_esup1 = realloc(_esup1, (sizeof(int))*(_istor));

			_esup1[_istor] = _ielem;

		}
	}

thank you very much (Ill be back in about 45 minutes, so if I doent reply it's not for rudeness!)
S.M.

Had a question about the lines highlighted red.

Code:

       int *_esup1;
	int *_esup2;
       int _szesup1;
        int CONN[][3] = {{1,2,6},{2,7,6},{2,3,7},{3,8,7},{3,4,8},{4,9,8},{4,5,9},{5,10,9},{7,8,13},{8,12,13},{8,9,12},{9,11,12},{9,10,11}};

       //Allocate _esup2:
	_esup2 = (int*) malloc((sizeof(int[nnode+1])));

       //First allocation of _esup1:
        _szesup1 = 1;
	_esup1 = malloc((sizeof(int))*(_szesup1); 
	
       //Store the elements in _esup1:
	for(_ielem=0; _ielem<=12; _ielem++){
		for(_inode=0; _inode<=2; _inode++){
		//Update storage counter, storing in _esup1:
			_ipoin = CONN[_ielem][_inode];

			_istor = _esup2[_ipoin-1] + 1; /* _esup2 is not initialized yet */

			_esup2[_ipoin-1] = _istor; /* sequence?? shouldn't the one above come after this one */
			
			_esup1 = realloc(_esup1, (sizeof(int))*(_istor));

			_esup1[_istor] = _ielem;

		}
	}

Originally Posted by Elysia

nnode, _istor and _ipoin is missing... I'll try hacking them in.
EDIT: Done. Got a crash. I will investigate.

Im back; here some numbers and types that I am actually using to run this:

int _ielem;
int _inode;
int _istor;
int nnode = 13;

I have a main.c written on purpose to test this function; I can send them both to you by this thread if you think it may help. The reason why I ask is due to the fact that the main.c and the function use much more variables than those already appearing in this thread, and that may cause some confusion.

Please those interested, let me know if you want the two codes as well

Thanks you
S.M.