Vector function emplace() My emplace function does not work. Any help would be appreciated
vector <int> vec1; vector <int> vec2(4,0); vector <int>::iterator iter1; vector <int>::iterator iter2; srand(time(NULL)); for(i=0; i<5; i++){ n =rand()%10+1; vec1.push_back(n); } for(iter1=vec1.begin();iter1<vec1.end();iter1++){ for(iter2=vec2.begin();iter2<vec2.end();iter2++){ if(*iter1<=*iter2){ //vec2.emplace(iter1,*iter1); //print(); } } } 
for(iter2=vec2.begin();iter2<vec2.end();iter2++){ Because vec2 starts populated with four values of 0, you will never find an element where *iter1 <= *iter2 unless *iter1 == 0.
Instead of zero-initializing it to avoid allocations, you want to reserve space.
vec2.reserve(vec1.size()); and then instead of a for loop you can use std::lower_bound to find the insert location:
#include <iostream> #include <vector> #include <algorithm> void print_vec(const char* label, const std::vector<int>& vec) { std::cout << label << ": "; for (int v : vec) { std::cout << v << ", "; } std::cout << "\n"; } int main() { std::vector <int> vec1 { 4, 1, 2, 2, 5 }; std::vector <int> vec2; print_vec("v1", vec1); vec2.reserve(vec1.size()); for (int v : vec1) { auto it = std::lower_bound(vec2.begin(), vec2.end(), v); if (it == vec2.end() || *it != v) vec2.emplace(it, v); print_vec("v2", vec2); } print_vec("Fin", vec2); return 0; } Live demo: http://ideone.com/o5td9K
What you are trying to do is like insertion sort. https://en.wikipedia.org/wiki/Insertion_sort has the pseudo-code. At each step you will check every element in vector 2 and place the new element where it belongs (while loop).
