STL Vector memory allocation issues

[kwisatz]

HI All,

have a struct which has a vector defined

typedef struct X_
{
...
..
vector<int> y;
..
} X;

Now in my main program, I first allocate memory to X

Xinstant = (X*) malloc(sizeof(X ));

So do I need to allocate seperate space for the vector?

When I try Xinstant->y.push_back(wh atever), I get runtime errors - seg faults.
Any problem here?

Thanks!
-k

[Banfa]

I think your trouble is that you are using malloc, try using new.

One of the things that new does (that malloc does not) is ensure that all the constructors for classes (and structures) are called correctly.

The way your code currently is I do not think that the vectors constructor is being called.

[kwisatz]

Thanks for the reply, but it *barely* worked.

The issue is this:

I have function fun1(){
X* Xinstant;

Xinstant = (X*) new X;
..
..
fun2(Xinstant);
}

fun2(Xinstant)
{
Xinstant->push_back(what ever) <---- I get a "what(): St9bad_alloc error"

}

I don't see what the problem is..
thanks!

k

[Ganon11]

Thanks for the reply, but it *barely* worked.

The issue is this:

I have function fun1(){
X* Xinstant;

Xinstant = (X*) new X;
..
..
fun2(Xinstant);
}

fun2(Xinstant)
{
Xinstant->push_back(what ever) <---- I get a "what(): St9bad_alloc error"

}

I don't see what the problem is..
thanks!

k

First of all, the typecast you have for creating XInstant is unnecessary. The new operator automatically allocates memory for the object, calls its constructor, and returns a pointer to that object. In other words, the new operator is like a function that returns a pointer - in this case, a pointer of type X*. So you can redo this statement as

Xinstant = new X;

Next, are you making sure that, when you push_back(whate ver), that 'whatever' is of type int? It would be bad if you were pushing back a double, for example, and this could produce a bad_alloc error (as the compiler allocating int memory, not double memory).

[kwisatz]

yep. I do Xinstant->y.push_back((i nt)whatever)

But now I get the following error:
SIGSEGV :

std::_Construct <int, int> (__p=0x4f000000 0b, __value=@0x7fff ffb2f9d8)
at stl_construct.h :81
81 ::new(static_ca st<void*>(__p)) _T1(__value);

Clearly its a memory issue, but I can't seem to place why this is happening.
Xinstant has other members as well, and they are all assigned. I get this problem with the vector only..

Thanks much for the replies, much appreciated.

-k

[kwisatz]

ok solved the problem. I replaced all my mallocs with new and seems to be working now. Thanks much again!
-k

[Ganon11]

I wasn't into programming when malloc() was standard, but I suppose mixing your mallocs and news can mess a lot of stuff up. Glad to see you got it working.