Thread: array of std::string pointers

If someone could help me out that would be great! I'm trying to assign values to an array of std::strings, declared from gSOAP as follows:

Code:

class bla
{ public:
    std::string* *__ptr;
    int __size;
    struct soap *soap;
};

Then I try to assign values like this:

Code:

bla* user = new bla;
bla->__size = 5;
bla->__ptr = (std::string **)soap_malloc(bla->soap, sizeof(std::string *) * bla->__size);

std::vector <std::string> v;
for (int i=0; i < 5; i++) {
  v.push_back(someFunctionReturningC_STR(i));
  bla->__ptr[i] = &v.back();
}

I'm using a vector only because that's the only thing I found that actually compiles, but running this code gives a runtime error; I suspect &v.back() is at fault.

So I have 2 questions, 1) how do I assign string data to my array? (although in my example the array is of fixed length, in my application the array will not be fixed), and 2) can you get a pointer to a specific element of the vector data? to read only, not to write...

Thanks

Luc

Code:

class bla
{ public:
    std::string* *__ptr; // I doubt you intended to have a pointer to a pointer
    ...

I think that's the real issue with your code. I wonder why you don't have a constructor for bla though. If there is a reason beyond "I don't know what a constructor is," ignore me.

> 2) can you get a pointer to a specific element of the vector data? to read only, not to write...
Yes, creating a const pointer to the element is one option.

the class declaration is a stub automatically generated from a WSDL document using gSOAP, and it works fine for receiving data from the server, but I'm trying to populate the structure to send data back to the server... I just can't figure out how to populate the information back... since it's pointers to pointers I can't just assign values, I need to create something that can be referenced by a pointer... I've never used vectors before but it seemed like a good option.. ?

I figured it out..

Code:

bla* user = new bla;
bla->__size = 5;
bla->__ptr = (std::string **)soap_malloc(bla->soap, sizeof(std::string *) * bla->__size);

std::vector <std::string> v;
for (int i=0; i < 5; i++) 
  v.push_back(someFunctionReturningC_STR(i));

std::vector <std::string>::iterator iv;
int i = 0;
for (iv = v.begin(); iv != v.end(); iv++) {
  bla->__ptr[i] = &(*iv);
  i++;
}

Not sure if this is the best way, I'm sure there's more than one way to do this...

what does everyone think? would a list be better? or some other data structure altogether?

thanks!

It's not actually 5 is it..

>> since it's pointers to pointers I can't just assign values, I need to create something that can be referenced by a pointer

I mean, if it is, you could have just:

Code:

for(int i = 0; i < 5; ++i)
{
    bla->__ptr[i] = new std::string(someFunctionReturningC_STR(i));
}

hehe, wow.. look at how simple that is. It works too. Thanks.

One question, I'm not very familiar with memory management in C, say I do what you suggest, is the memory allocated by the new std::string reserved until the end of the function? Even though it's not specifically assigned to a variable? I know it's assigned to __ptr, but that's just a pointer to an address right?

ok.. so if I do this..

Code:

void function foo() {
  for(int i = 0; i < 5; ++i)
  {
    bla->__ptr[i] = new std::string(someFunctionReturningC_STR(i));
  }
}

I need to delete them later? like..

Code:

  for(int i = 0; i < 5; ++i)
  {
    delete bla->__ptr[i];
  }

that?

Yah.