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STL::vector problem

Hi,

I have vector with some elements. now I want to search particular
element and find out the position of that element in that vector (
index ). I used find algorithm but it gives Iterator in return.
please help me to find out position of any element in that vector .

any help is welcome
Thanks

Rahul

Sep 23 '05 #1
6 9015

"LinuxGuy" <ra**********@gmail.com> wrote in message
news:11*********************@g44g2000cwa.googlegro ups.com...
Hi,

I have vector with some elements. now I want to search particular
element and find out the position of that element in that vector (
index ). I used find algorithm but it gives Iterator in return.
please help me to find out position of any element in that vector .

any help is welcome
Thanks

Rahul


#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
std::vector<int> vec;
vec.push_back(42);
vec.push_back(99);
vec.push_back(25);
vec.push_back(32);

int value(25);

std::vector<int>::const_iterator it
(std::find(vec.begin(), vec.end(), value));

std::cout << "Value " << value;

if(it != vec.end())
std::cout << " found at vector element "
<< it - vec.begin();
else
std::cout << " not found";

std::cout.put('\n');
return 0;
}

-Mike
Sep 23 '05 #2
This is just a wild guess - and probably not the right way but can't
you do something like

int index = (objaddr - firstobj_addr) / sizeof(object)

Sep 23 '05 #3
For an iterator 'i' into vector 'v', use

int index = (int)std::distance(v.begin(), i);

to find the index.

(This will break down if your vector is so large that an int can't
store the index - in which case look at the actual return type of
std::distance)

Sep 23 '05 #4
>> int index = (int)std::distance(v.begin(), i); to find the index.

instead, use :
std::vector<int>::difference_type index;
index = std::distance (v.begin(), i );
std::cout << "\n Position in the vector: " << index << "th Element from
the begining of the vector " << std::endl ;
~hth
M

Sep 23 '05 #5
LinuxGuy wrote:
Hi,

I have vector with some elements. now I want to search particular
element and find out the position of that element in that vector (
index ). I used find algorithm but it gives Iterator in return.
please help me to find out position of any element in that vector .

any help is welcome
Thanks

Rahul


Given a vector v, and an iterator, iter, in v, the expression:

iter - v.begin()

calculates the "position" (or index) of the element in v that iter
references.

Greg

Sep 23 '05 #6

tmartsum schreef:
This is just a wild guess - and probably not the right way but can't
you do something like

int index = (objaddr - firstobj_addr) / sizeof(object)


Addresses differences are expressed in numbers of objects in between,
not bytes. Therefore, you don't have to divide by sizeof, and secondly,
there must be objects in between (or allocated memory where they could
be constructed).

The basic idea is right, though, but you don't need the address when
you have an iterator. (objIter-firstObjIter) works just as well, and
it also works for std::deque (=>more general solution)

HTH,
Michiel Salters

Sep 23 '05 #7

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