CODEWITHSUNDEEP
c++for-loopc++11stliterator
Gottfried
Gottfried

Reputation: 2139

How to iterate through a list of objects in C++?

I'm very new to C++ and struggling to figure out how I should iterate through a list of objects and access their members.

I've been trying this where data is a std::list and Student a class.

std::list<Student>::iterator<Student> it;
for (it = data.begin(); it != data.end(); ++it) {
    std::cout<<(*it)->name;
}

and getting the following error:

error: base operand of ‘->’ has non-pointer type ‘Student’

Upvotes: 99

Views: 383985

Answers (5)

yoni fram
yoni fram

Reputation: 41

If you add an #include <algorithm> then you can use the for_each function and a lambda function like so:

for_each(data.begin(), data.end(), [](Student *it) 
{
    std::cout<<it->name;
});

You can read more about the algorithm library at https://en.cppreference.com/w/cpp/algorithm

and about lambda functions in cpp at https://learn.microsoft.com/en-us/cpp/cpp/lambda-expressions-in-cpp?view=vs-2019

Upvotes: 4

Guy Avraham
Guy Avraham

Reputation: 3690

It is also worth to mention, that if you DO NOT intent to modify the values of the list, it is possible (and better) to use the const_iterator, as follows:

for (std::list<Student>::const_iterator it = data.begin(); it != data.end(); ++it){
    // do whatever you wish but don't modify the list elements
    std::cout << it->name;
}

Upvotes: 4

Radek
Radek

Reputation: 329

-> it works like pointer u don't have to use *

for( list<student>::iterator iter= data.begin(); iter != data.end(); iter++ )
cout<<iter->name; //'iter' not 'it'

Upvotes: 3

jhill515
jhill515

Reputation: 943

Since C++ 11, you could do the following:

for(const auto& student : data)
{
  std::cout << student.name << std::endl;
}

Upvotes: 24

Simple
Simple

Reputation: 14390

You're close.

std::list<Student>::iterator it;
for (it = data.begin(); it != data.end(); ++it){
    std::cout << it->name;
}

Note that you can define it inside the for loop:

for (std::list<Student>::iterator it = data.begin(); it != data.end(); ++it){
    std::cout << it->name;
}

And if you are using C++11 then you can use a range-based for loop instead:

for (auto const& i : data) {
    std::cout << i.name;
}

Here auto automatically deduces the correct type. You could have written Student const& i instead.

Upvotes: 166

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