Get the closest point to a desired coordinate in a 2D space

ClosestToPoint2D.cc

#include "iostream"
#include "vector"
#include <math.h>

struct Vec3 {
  float x,y,z;
};

template <class T>
Vec3 getClosest(std::vector<T> withPosVec, const Vec3 toPos) noexcept {

  float a;
  float b;

  // closest item of the vector above, we setup a base z wich (in our case is unused
  // because we work on a 2D space then we uuse it to store the distance) is unreachable
  Vec3 closest { 0, 0, (toPos.x + toPos.y) };

  // iterate in the vector containing the positions
  for ( Vec3& entry: withPosVec ) {

    // Make sure we have absolute value
    a = std::abs(entry.x - toPos.x);
    b = std::abs(entry.y - toPos.y);

    // basic Pythagorean calculation and checking if the result is lower of the current closest
    if ( (entry.z = sqrt((a*a) + (b*b))) < closest.z )
      closest = entry;
    
    std::cout << "(" << entry.x << ", " << entry.y << ") = " << entry.z << '\n';
  }

  return closest;
}

int32_t main() {

  // Vector of positions to test
  std::vector<Vec3> positions = {
    { 1285.f, 810.f, 0.f },
    { 1283.f, 801.f, 0.f },
    { 1500.f, 808.f, 0.f },
    { 1300.f, 800.f, 0.f },
    { 1700.f, 400.f, 0.f },
    { 700.f, 1000.f, 0.f },
    { 200.f, 890.f, 0.f },
    { 2000.f, 1200.f, 0.f },
    { 239.f, 20.f, 0.f },
    { 20.f, 89.f, 0.f }
  };

  Vec3 closest = getClosest(positions, { 1280.f, 800.f, 0.f });

  std::cout << "Closest is { " << closest.x << ", " << closest.y << ", " << closest.z << " }" << '\n';

}

/* Output:
(1285, 810) = 11.1803
(1283, 801) = 3.16228
(1500, 808) = 220.145
(1300, 800) = 20
(1700, 400) = 580
(700, 1000) = 613.514
(200, 890) = 1083.74
(2000, 1200) = 823.65
(239, 20) = 1300.8
(20, 89) = 1446.76
Closest is { 1283, 801, 3.16228 }
*/