Help with malloc()

[Schizoid Man]

Hi,

I have a function in which I am reading in an integer value, and
dynamically creating an array of type double and size of the integer value:

double compute(int steps, int typeopt)
{
double *price_array;

price_array = (double *) malloc(sizeof(i nt) * steps);

...

}

So far so good.

Now in my main method, I invoke this function twice:

value = compute(steps, 0);
printf("\n%5.5l f", value);

value = compute(steps, 1);
printf("\n%5.5l f", value);
I get a correct answer for the first time it is invoked, but I get the
following error when the function is invoked the second time (i.e
typeopt = 1): Unhandled exception at 0x00411816: 0xC0000005: Access
violation writing location 0x00000000.

I then go back to the compute method and put a free(price_arra y);
statement at the end of the method.

I then get the following message:

HEAP: Heap block at 00355870 modified at 0035606C past requested size of
7f4 Windows has triggered a breakpoint. This may be due to a corruption
of the heap, and indicates a bug in or any of the DLLs it has loaded.
The output window may have more diagnostic information.

I would really appreciate any help at all.

Thanks in advance,
Schiz

[Keith Thompson]

Schizoid Man <sc***@sf.comwr ites:
[...]

I was already including stdlib.h, but your suggestion did help me
out. If I discard the cast then I get the following error:

error C2440: '=' : cannot convert from 'void *' to 'double *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast

However, if I use the cast then the method works perfectly. Thanks for
the help.

An implicit conversion from void* to double* (or to any
pointer-to-object type) is perfectly legal in C. The most likely
explanation for the error message is that you're using a C++ compiler.

If you have questions about C++, you'll need to ask in comp.lang.c++,
<OT>and you should probably be using new rather than malloc()</OT>.
If you intend your code to be valid C, use a C compiler.

Casting the result of malloc() is required in C++, and strongly *not*
recommended in C. (Some people may post followups here saying that
you should cast the result of malloc() in C; except in some very
narrow circumstances, they're wrong, for reasons that have been
explained here many times.)

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Schizoid Man]

Richard Heathfield wrote:

Schizoid Man said:

<snip>

>I was already including stdlib.h, but your suggestion did help me out.
If I discard the cast then I get the following error:

error C2440: '=' : cannot convert from 'void *' to 'double *'
Conversion from 'void*' to pointer to non-'void' requires an explicit cast

Then I strongly recommend that you either rename your file from foo.cpp to
foo.c, or ask in comp.lang.c++ in future.

C and C++ are different languages, with different rules. Asking in a C group
about a C++ program doesn't make much sense.

Hi Richard, Martin, Keith,

You're all absolutely right - I am using Microsoft Visual C++. I did
know that an implicit conversion from void to double is legal, so I was
wondering why I get this error without the cast.

Renaming it to .c should do the trick.

Thanks for the help, and sorry for the bother.