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May 2nd, 2005

passing vector to a pointer?

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I have a project where I must use pointers to do a search on some accounts I've built up into a vector. My problem is whenever I try to pass the vector to a pointer I get an error. I've tried many different things but to no avail. Maybe one of you can tell me what I'm doing wrong?

This is basically what I'm trying to do:

C++ Syntax (Toggle Plain Text)
#include <vector>
using namespace std;
 
double * func()
{
vector<double> vec;
return vec;
}
 
int main()
{double * p;
p=func();
 
return 0;
}
#include <vector>
using namespace std;

double * func()
{
vector<double> vec;
return vec;
}

int main()
{double * p;
p=func();

return 0;
}

The error I get:

Quote ...

test.cpp: In function `double* func()':
test.cpp:7: cannot convert `std::vector<double, std::allocator<double> >' to `
double*' in return

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passing a vector to a function? :errors: in C++

XxAndyxX

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May 2nd, 2005

Re: passing vector to a pointer?

C++ Syntax (Toggle Plain Text)
double * func()
{
vector<double> vec;
return vec;
}
double * func()
{
vector<double> vec;
return vec;
}

I don't think there is a typecast for double to vector<double>. What you should do is use a pointer to a vector<double> variable:

C++ Syntax (Toggle Plain Text)
vector<double> * func()
{
     vector<double> vec;
     return vec;
}
vector<double> * func()
{
     vector<double> vec;
     return vec;
}

That should work, but no guarantees since I didn't test it. Also, you may wish to change your double pointer in main() to a pointer to vector<double>.

Now, if you are trying to use the pointer to double for data in the vector, you may wish to just use an iterator.

marinme

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May 2nd, 2005

Re: passing vector to a pointer?

For this assignment we are required to use a pointer to search through an array (or vector) of accounts. Why doesn't this work?

C++ Syntax (Toggle Plain Text)
vector<account> vec_account; //creates a vector of accounts
vector<account> * p; //creates a pointer to a vector of accounts
get_accounts(vec_account); //fills the vector with accounts
p=vec_account; //stores the base address of the vector into the pointer -but I get an error?  Logically it makes since to me...
 
ERROR I GET IS:
code.cpp:266: cannot convert `std::vector<account, std::allocator<account> >'
   to `std::vector<account, std::allocator<account> >*' in assignment
vector<account> vec_account; //creates a vector of accounts
vector<account> * p; //creates a pointer to a vector of accounts
get_accounts(vec_account); //fills the vector with accounts
p=vec_account; //stores the base address of the vector into the pointer -but I get an error?  Logically it makes since to me...

ERROR I GET IS:
code.cpp:266: cannot convert `std::vector<account, std::allocator<account> >'
   to `std::vector<account, std::allocator<account> >*' in assignment

Here is the search algorithm I'll be using to search through the vector of accounts:

C++ Syntax (Toggle Plain Text)
 
for (match=0; p <  (p+v.size()) && match==0; ++p)
  if (acct_num==p->read_acct_num()) match=1      //acct_num is given by the user
i--;
if (match==0) cout<<"\n\tACCOUNT NUMBER DOES NOT EXIST!\n";
else {
for (match=0; p <  (p+v.size()) && match==0; ++p)
  if (acct_num==p->read_acct_num()) match=1      //acct_num is given by the user
i--;
if (match==0) cout<<"\n\tACCOUNT NUMBER DOES NOT EXIST!\n";
else {

XxAndyxX

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May 3rd, 2005

Re: passing vector to a pointer?

It should work just using
p = &vec_account;

marinme

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May 3rd, 2005

Re: passing vector to a pointer?

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
 
vector<double> *func()
{
   static const double init[] = {1.0,1.5,2.0,3.3};
   vector<double> *vec = new vector<double>(init, init + sizeof init / sizeof *init);
   return vec;
}
 
int main()
{
   vector<double> *p = func();
   copy(p->begin(), p->end(), ostream_iterator<double>(cout, "\n"));
   return 0;
}
 
/* my output
1
1.5
2
3.3
*/
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;

vector<double> *func()
{
   static const double init[] = {1.0,1.5,2.0,3.3};
   vector<double> *vec = new vector<double>(init, init + sizeof init / sizeof *init);
   return vec;
}

int main()
{
   vector<double> *p = func();
   copy(p->begin(), p->end(), ostream_iterator<double>(cout, "\n"));
   return 0;
}

/* my output
1
1.5
2
3.3
*/

Dave Sinkula

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