Re: std::vector question related with gsl_vector

"Jim Langston" <>
Fri, 30 Mar 2007 23:10:57 -0700
"zl2k" <> wrote in message

hi, all

I need to use gsl_vector pointer with std::vector but not sure how to
free the memory when I don't need it. Here is a piece of the code.

std::vector<gsl_vector * > v;
gsl_vector * a = gsl_vector_alloc(3);
gsLvector_set(a, 0, 7);

gsl_vector_free(a); // problem! after a is free, the v[0] is null
std::cout<<gsl_vector_get(v[0], 0)<<std::endl;

How can I free the memory when I don't need them? If I say


will the memory allocated by the gsl_vector still hold by the
unreachable vectors?
Or should I do

for (int i = 0; i < v.size(); i++){

to free the memory? But iterating on each elements of the vector is
tedious if the std::vector is long. Is there any easy way to deal with
the problem? Thanks for comments.

You only need a pointer to the instance to use delete. Deleting the pointer
itself does not delete the instance. Some would advise smart pointer here.

All you have to remember is, you used new once, use delete once.

Lets show a simpler example.

int* a = new int;
int* b = a;

delete b;

Now both a and b point to invalid memory.

int * a = new int;
int* b = a;
a = NULL;
delete b;

We can still delete the memory since we have a pointer to it. Changing one
of the pointers itself does not change the fact the memory was allocated
with new and we need to call delete on it.

So, specific to your question, do not call
until you are done with your vector. You have 2 pointers pointing to the
same memory, a and an element in your std::vector. Go ahead and ignore a,
reuse it, whatever. It now longer "owns" the instance.

So, yes, after you are done with the vector, iterate through the vector and
delete (in yoru cass gsl_vector_free) the memory.

malloc and free are the same as new and delete, you call maloc/new once you
call free/delete once.

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