how to initialize a vector in the constructor

[zl2k]

hi, all
Suppose I have the following header file:

#include <vector>
using namespace std;

class Test{
public:
~Test();
Test();
private:
vector<int> v;
vector<vector<int> > vv;
}

Then in the Test.cpp, I have

Test::Test() : v(0), vv(0){}

Am I initialize the vector correct? At the time when the constructor is
excuted, I don't have the number to fill the vector yet, so I put them
to size of 0. (It seems I initialize them to null, but null is not
initialized, right?) Please correct me if I am doing wrong. I got
strange run time errors which indicating some of the parameters are not
initialized correctly. Thanks for help.

zl2k

 

[Alf P. Steinbach]

* zl2k:

hi, all
Suppose I have the following header file:

#include <vector>
using namespace std;

Don't put 'using namespace std;' in a header file.

It can also be a good idea to restrict its usage elsewhere.

See the FAQ item "Should I use using namespace std in my code?",
currently at <url:
http://www.parashift.com/c++-faq-lite/coding-standards.html#faq-27.5>.

class Test{
public:
~Test();
Test();
private:
vector<int> v;
vector<vector<int> > vv;
}

Then in the Test.cpp, I have

Test::Test() : v(0), vv(0){}

Am I initialize the vector correct?

Yes. You initialize both vectors to zero size. I.e. they're empty.

At the time when the constructor is
excuted, I don't have the number to fill the vector yet, so I put them
to size of 0. (It seems I initialize them to null, but null is not
initialized, right?) Please correct me if I am doing wrong. I got
strange run time errors which indicating some of the parameters are not
initialized correctly. Thanks for help.

See the FAQ item "How do I post a question about code that doesn't work
correctly?", currently at <url:
http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.8>.

 

[Daniel T.]

hi, all
Suppose I have the following header file:

#include <vector>
using namespace std;

class Test{
public:
~Test();
Test();
private:
vector<int> v;
vector<vector<int> > vv;
}

Then in the Test.cpp, I have

Test::Test() : v(0), vv(0){}

Am I initialize the vector correct?

That's one way to do it.

At the time when the constructor is
excuted, I don't have the number to fill the vector yet, so I put them
to size of 0. (It seems I initialize them to null, but null is not
initialized, right?) Please correct me if I am doing wrong. I got
strange run time errors which indicating some of the parameters are not
initialized correctly. Thanks for help.

Chances are, you are trying to access elements in one of the vectors
that don't exist yet.