CODEWITHSUNDEEP
c++listvectorstruct
Mike1982
Mike1982

Reputation: 459

Accessing structs in a vector of lists

I have a vector of lists of structs named Edge

so,

vector<list<Edge>> adjA;

and my struct looks like:

struct Edge {
   int weight;
   ... 
}

Assuming my adjA is already filled with Edges, how would I accessing those edges' variables?

vector<int>weights;
for(uint i = 0; i < adjA.size(); i++) //iterating through vector
{  for(uint j = 0; j < adjA[i].size(); j++) //iterating through list
   {
      weights.push_back(adjA[i][j].weight); //compiler error
   } 
}

error: 

no match for ‘operator[]’ (operand types are ‘__gnu_cxx::__alloc_traits<std::allocator<std::__cxx11::list<Edge> > >::value_type {aka std::__cxx11::list<Edge>}’ and ‘uint {aka unsigned int}’)
       weights.push_back(adjA[i][j].weight);

Thanks in advance

Upvotes: 0

Views: 338

Answers (3)

Sid S
Sid S

Reputation: 6125

std::list doesn't have an operator [] ()

You can use range-based for loops:

for (const auto &edges : adjA)
{
    for (const auto &edge : edges)
    {
        weights.push_back(edge.weight);
    }
}

Or iterators:

for (auto it = adjA.begin(); it != adjA.end(); it++)
{
    for (auto jt = it->begin(); jt != it->end(); jt++)
    {
        weights.push_back(jt->weight);
    }
}

Upvotes: 3

Woody1193
Woody1193

Reputation: 7980

According to this somewhat dated reference, list doesn't have a [] operator. Instead, try using an iterator:

for(std::list<Edge>::iterator it = adjA[i].begin(); it != adjA[i].end(); ++it)
{
    weights.push_back(it->weight);
}

Upvotes: 0

unlut
unlut

Reputation: 3775

You can not access elements of stl list with [] operator, however you can use iterators to iterate list: 

vector<int>weights;
for(uint i = 0; i < adjA.size(); i++) //iterating through vector
{  
    for (std::list<Edge>::iterator it = adjA[i].begin(); it != adjA[i].end(); ++it)
    {
        weights.push_back(it->weight);
    }
}

Upvotes: 2

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