Question regarding std::Vector....

[Raza5680]

Hi, I am working with images and computing radon transform for an object. the function that computes the transform accepts vector as input:

pixel p;
vector segObj //segObj is the object segmneted from the image

pixel is a user-defined struct defined as:

struct pixel
{
float x, y; //x,y coordinates of the pixel
};

Currently, I am doing an element wise assignment to the vector:

for(int ix=0; ix < element_count; ix++)
{
{
f.x = xCoordArray[ix];
f.y = yCoordArray[ix];
segObj.push_back(f);
}
}

//xCoordArray and yCoordArray are computed separately The for loop makes it slow when dealing with large images. Is there a way to assign xCoordArray and yCoordArray directly to

vectorsegObj

I am not expereinced with the use of vectors so any help would be appreciated Thanks

[Andre Kraak]

You might try using reserve[^] before your loop. This will allocate the memory in one go for the vector and prevent the reallocation of memory every time you call push_back. So try adding

segObj.reserve( element_count );

before the for loop.

0100000101101110011001000111001011101001

[Raza5680]

There is a little improvement but for cases with more coordiante values ( > 2000) it is still slow. I am trying to get rid of the for loop, since at each index there a two values (pixel coordinates) using .assign is a bit tricky for me thanks

[_Superman_]

If speed is a concern to you, you must use xCoordArray and yCoordArray as is without using the vector.

«_Superman_»  _I love work. It gives me something to do between weekends.

_Microsoft MVP (Visual C++)

Polymorphism in C

[Raza5680]

Thanks for the reply. The issue is the function I am using accpets vector as input and re-writing it is not possible at the moment.

[Chris Losinger]

you could try:

segObj.resize(element_count);
for(int ix=0; ix < element_count; ix++)
{
segObj[ix].x = xCoordArray[ix];
segObj[ix].y = yCoordArray[ix];
}

that eliminates the push_back, at least.

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