int main()
{
vector<vector <int>> a={{1,2,3,4,5,6},{2,4,7,8},{1,2}};
for (auto c: a)
{
cout<<c;
}
}
the compiler is throwing error:
no match for ‘operator<<’ (operand types are ‘std::ostream’ {aka ‘std::basic_ostream<char>’} and ‘std::vector<int>’)
cout<<c;
i want to use the same syntax of the for loop to traverse 2-D vectors , perhaps it is related to operator overloding , but i dont know how to fix it , can anybody help ?
thanks.
what do you mean by code link ? sorry i am new to these jargons.
On line 7 make a correction
vector<vector<int> > a={{1,2,3,4,5,6},{2,4,7,8},{1,2}};
add a space between > and >
Firstly, Format your code.
Either do this
for(const auto &vec : a){
for(const auto &c : vec){
cout<<c<<" ";
}
cout<<'\n';
}
or
declare this at the top of your code
ostream& operator<<(ostream& out, const vector<vector<int>> &vec){
for(int i=0;i<vec.size();i++){
for(int j=0;j<vec[i].size();j++){
out<<vec[i][j]<<" ";
}
out<<'\n';
}
return out;
}
Then you can type this
cout<<a;
thank you for your reply, I want to know more about the second approach and operator overloading, can you suggest some resources.
And can you please tell me why you have used const for the pointer?
Thanks.
Because I’m not changing the value. it’s good practice to always declare constant variables as const.
operator overloading syntax is
"return value" operator"operator symbol"("left operand", "right operand"){
//actual code here
}
template<typename T>
can be used when you want the operator to do the same thing for many data types. The compiler will fill in the datatype for you.
Here’s a small example on how to use them.
cin is of type istream and cout is ostream
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
template<typename T>
ostream& operator+(ostream& out, const vector<T> &vec){
for(const auto &x : vec){
out<<x<<" ";
}
out<<"\n";
return out;
}
template<typename T>
istream& operator-(istream& in, vector<T> &vec){
for(auto &x : vec){
in>>x;
}
return in;
}
template<typename T>
void operator++(vector<T> &vec){
T value;
vec.push_back(value);
}
template<typename T>
void operator--(vector<T> &vec){
vec.pop_back();
}
template<typename T>
void operator+=(vector<T> &vec, T val){
vec.push_back(val);
}
template<typename T>
void operator+=(vector<T> &vec1, vector<T> &vec2){
for(const auto &val : vec2){
vec1+=val;
}
}
void solve(){
int n;
cin>>n;
vector<int> seq(n);
cin-seq;
seq+=2;
++seq;
cout+seq;
--seq;
vector<int> seq2={1,3,4};
seq+=seq2;
cout+seq;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
solve();
}
thank you so much