optimising the factors such as resizing and copying

Optimising usage -- (std vector)/Log.cpp

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+#include <iostream>
+#include <string>
+#include <vector>
+
+struct Vertex
+{
+    float x, y, z;
+
+    Vertex(float x, float y, float z)
+              : x(x), y(y), z(z)
+          {
+          }   
+ Vertex(const Vertex& vertex)
+            :x(vertex.x), y(vertex.y), z(vertex.z)
+ {
+                std::cout << "Copied!" << std::endl;
+ }         
+
+};
+
+int main()
+  {
+
+    std::vector<Vertex> vertices;
+    vertices.reserve(3);  
+
+    vertices.emplace_back(1, 2, 3);
+    vertices.emplace_back(4, 5, 6);
+    vertices.emplace_back(7, 8, 9);       
+
+    std::cin.get();
+  }
+
+
+// to optimise vertex that constructing inside main  and copied to vector class,just construct in vector class itself
+// just pass the parameter list itself in place of vertex object to get constructed in vector class itself
+//tells vector construct a vertex object with the following parameters in place in our actual vector memory

Optimising usage -- (std vector)/main.cpp

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+#include <iostream>
+#include <string>
+#include <vector>
+
+struct Vertex
+{
+    float x, y, z;
+
+    Vertex(float x, float y, float z)
+              : x(x), y(y), z(z)
+          {
+          }   
+ Vertex(const Vertex& vertex)
+            :x(vertex.x), y(vertex.y), z(vertex.z)
+ {
+                std::cout << "Copied!" << std::endl;
+ }         
+
+};
+
+int main()
+  {
+
+
+    std::vector<Vertex> vertices;
+    vertices.reserve(3);       //takes capacity of 3 and its not resizing by copying or giving it in constructor is saying just construct it 3 vertices objects vertices(3) but we want memory
+
+    vertices.push_back(Vertex(1, 2, 3));
+    vertices.push_back(Vertex(4, 5, 6));
+    vertices.push_back(Vertex(7, 8, 9));       // via defualt constructor
+
+    std::cin.get();
+  }
+
+
+//This is about optimising using of std::vector class on reallocation and copying [slow code]
+// rules of optimisation is basically knowing your environment
+//how do things work and what do i need to do exactly and what should happen
+// so now optimising about reducing copying our objects!! especially object storing vector class
+// WE NEED TO KNOW WHEN COPY CONSTRCTOR CALLING
+// constructing this vertex object on inside of our main funtion stack frame then pushing[copying] it to the vertices vector cause copy so can we construct that vertex in place of actual memory vector allocated to us 
+// vector resizing twice here one by defualt and 2 when moves to 2nd element and 3 moving to 3rd element
+// make enough memory to hold vector from beggining is optimising 2