向量的格式说明符 <Vec3b> 什么时候使用printf

Question

I want to fetch, let us, say second pixel in buf and print using printf:

vector<Vec3b> buf;
/* code that fills buf , I used push_back */
printf("%WHAT", buf[1])

I can print these values using cout something like this:

    LineIterator it(img, Point(1,1), Point(20,20), 8);

    vector<Vec3b> buf;   

    for(int i=0; i<it.count; i++)
    {
    buf.push_back( Vec3b(*it) ); /* code that fills buf , I used push_back */
    it++;
    }
    cout << Mat(buf[1]) << endl;

But I just want to do this using printf.

The cout statement gives me three values, each corresponding to R, G and B.

What should I place for WHAT in my printf? ie what is the format specifier here?

Answer 1

there's no straightforward way to do so. there are overloaded << operators in opencv, but no c solution (why do you even want this?)

you will have to do it all manually:

for(size_t i=0; i<buf.size(); i++)
{
   Vec3b v = buf[i];
   printf("[%d %d %d] ", v[0], v[1], v[2] );
}
printf("\n");

Answer 2

You wont be able to just use it with printf like that because its not of a standard type. I think you should write a function to print this type for you, for example something like this:

void printForMe(vector<Vec3b> buf)
{
    for (auto &vec : buf)
    {
        cout << vec[0] << " " << vec[1] << " " vec[2] << std::endl;
    }
}

You can then also edit how your format will appear.

This would be even easier if OpenCv's MatX class had an overload for operator<< but it doesn't so you will need to make this yourself.