vector resize doesn't work? [closed] - c++

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I have 3 maps with a string as key and a vector as value.
std::map<std::string, std::vector<int> > m_attri; ///< Attributes of type int
std::map<std::string, std::vector<double> > m_attrd; ///< Attributes of type double
std::map<std::string, std::vector<std::string> > m_attrs; ///< Attributes of type std::string
I have a function that resizes them all, calles SetNum()
void SetNum(size_t n)
{
std::cout << "setting num: " << n << std::endl;
m_num = n;
for (auto attr : m_attri) {
attr.second.resize(n, 0);
std::cout<<attr.second.size();
}
for (auto attr : m_attrd) {
attr.second.resize(n, 0.0);
std::cout<<attr.second.size();
}
for (auto attr : m_attrs) {
attr.second.resize(n, "");
std::cout<<attr.second.size();
}
std::cout<<std::endl;
}
this all seems to work, when is say setnum(1), I get a bunch of 1s as output.
Now the problem lies here, I have another function called Set
template<typename T>
inline void AttributeContainer::Set(size_t node_idx, const std::string& name, T value)
{
std::cout << GetNum() << node_idx << ',' << std::endl;
if( node_idx >= GetNum()){
SetNum(node_idx+1);
}
auto attr_kv = Attributes<T>().find(name);
if (attr_kv != Attributes<T>().end()) {
std::cout<<"Containersize: " << attr_kv->second.size() << ',' << "id:"<< node_idx<< std::endl;
attr_kv->second.at(node_idx) = value;
std::cout<<"ContainersizeDone: " << attr_kv->second.size() << std::endl;
} else {
throw std::runtime_error("AttributeContainer::Set(): attribute not found: " + name);
}
}
node_idx is 0 and the vector is found. But it seems that the resize didn't work, because, altough I get output that confirms it is resized, i get a out_of_range exception from at and the line above shows that the size is 0. Now this is weird, as I thought that I succesfully resized them?

Answer 1

In SetNum, you are iterating over your map by value (see this post)
Consequently, you are applying resize on copies of your stored vectors.
What you want is to use auto& :
void SetNum(size_t n)
{
std::cout << "setting num: " << n << std::endl;
m_num = n;
for (auto& attr : m_attri) {
attr.second.resize(n, 0);
std::cout<<attr.second.size();
}
for (auto& attr : m_attrd) {
attr.second.resize(n, 0.0);
std::cout<<attr.second.size();
}
for (auto& attr : m_attrs) {
attr.second.resize(n, "");
std::cout<<attr.second.size();
}
std::cout<<std::endl;
}