This use of iterators crashes.

[joseplusplus]

Hello, Well... actually I have a short piece of code I would like that you guys analyze.
I'm using pointers to iterators but certainly I'm doing it wrong

#include <iostream>
#include <vector>

using std::string;
using std::cout;
using std::cin;
using std::endl;
using std::vector;

double sum_vec(vector<double>::iterator*, vector<double>::iterator*);

int main() {
	vector<double> vec(3, 10.5);
	vector<double>::iterator start = vec.begin();
	vector<double>::iterator end = vec.end();
	cout << "Sum of doubles is " << sum_vec(&start, &end) << endl;
	return 0;
}

double sum_vec(vector<double>::iterator *start, vector<double>::iterator *end) {
	double sum = 0.0;
	for( ; start != end; ++start) 
		sum += **start;
	return sum;
}

I was hoping someone could tell me where's my mistake because this little program just crashes.

Thanks in advance.
Jose.

[Disch]

You're treating begin and end like they're iterators... and you're doing that properly.

However you have pointers to iterators, so it's wrong.

The easiest solution is to not use pointers:

double sum_vec(vector<double>::iterator, vector<double>::iterator);  // no pointers

//...

double sum_vec(vector<double>::iterator start, vector<double>::iterator end) {
	double sum = 0.0;
	for( ; start != end; ++start)   // this is right if you have iterators
		sum += *start;  // only one * to deref an iterator
	return sum;
}

If you want to change it to be pointers to iterators (but I really don't advise it!) you can do it this way:

double sum_vec(vector<double>::iterator* start, vector<double>::iterator* end) {
	double sum = 0.0;
	for( ; *start != *end; ++(*start))  // note the changes here
		sum += **start;
	return sum;
}

[guestgulkan]

for( ; start != end; ++start) //incorrect dereferencing of your pointers - 3 times



((I assume you are doing this for some test purposes - but there is no need to
pass the parameters by pointer anyway))

[joseplusplus]

Hello,

thanks for the replies, I've fixed it now. but you're right, I'm doing it for testing only, and I really need to know how could I fix the line you (guestgulkan) have so adequatly put:

for( ; start != end; ++start) //incorrect dereferencing of your pointers - 3 times

so that I can preserve my original function declaration.. that is:

double sum_vec(vector<double>::iterator*, vector<double>::iterator*);

like that...

Could you please tell me how to correctly dereference in this case ?

Thank you once again,

Jose.

[Disch]

I already answered that in my post.

[joseplusplus]

I must be blind, I apologize !

Thank you very much Disch, I've noticed you've taken the time to carefully reply many of my questions, I must express my most sincere gratitude, You're really helping me to improve my abilities in the C++ programming language.

Thank you Thank you Thank you !

Keep up the fantastic work.

Jose.