Accessing class member inside a vector

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Hi I am new to C++
I have a vector iterator It, which has a Class A inside it and class has double variable b.
I need to access the variable so I wrote something like this:
It.A->b
but its throwing me different errors.
can someone tell me the correct format?

Posted 14-Jul-13 18:16pm

diasblood

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2 solutions

Solution 2

Just as a remark, I would not use an iterator with a vector, but just use the index. For example:

C++

    std::vector<double> vec;
    ...
    double d = vec[i];
</double>

If you insist in using an iterator, then think of it as being kind of a pointer (syntax wise), and hence you would dereference it as:

C++

    std::vector<mystruct> vec;
    ...
    MyStruct* p = it;
    ... or if age is a member of MyStruct
    int age = it->age;
</mystruct>

Posted 14-Jul-13 19:52pm

nv3

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H.Brydon 15-Jul-13 12:16pm

There should be no problem using an iterator on vector<whatever>. This type of sequential access is supposed to be (slightly) faster than an index lookup in a loop, even for vector<>.

nv3 15-Jul-13 14:21pm

I wasn't worried about performance, as todays's optimizer will probably produce equally efficient code for both cases. But a simple loop over an integer index is in my opinion easier to write and to understand than the somewhat typing intensive iterator syntax. -- Just a matter of taste I guess.

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H.Brydon · Accepted Answer · 2013-07-14T18:17:00

Solution 1

You need to dereference the iterator. What you want is

C++

*It->b

[rev.1 - sorry, syntax error, hopefully fixed...]

Posted 14-Jul-13 18:17pm

H.Brydon

Updated 14-Jul-13 18:45pm

v2

Comments

diasblood 15-Jul-13 0:40am

it gives an error on *It (Expression must have pointer to class type)

diasblood 15-Jul-13 0:48am

still same error on It

H.Brydon 15-Jul-13 0:59am

Try this:

A* ptr = *It;
double x = ptr->b;

This should be the same as

double x = *It->b;

with extra layers of unrolling the onion.

diasblood 15-Jul-13 10:21am

the first solution worked. I was missing a function call earlier.
Thanks a lot