All Questions
2,879
questions
311
votes
17
answers
389k
views
vector vs. list in STL
I noticed in Effective STL that
vector is the type of sequence that
should be used by default.
What's does it mean? It seems that ignore the efficiency vector can do anything.
Could anybody ...
- 25.5k
287
votes
15
answers
302k
views
Can you remove elements from a std::list while iterating through it?
I've got code that looks like this:
for (std::list<item*>::iterator i = items.begin(); i != items.end(); i++)
{
bool isActive = (*i)->update();
//if (!isActive)
// items.remove(*...
- 35k
139
votes
9
answers
104k
views
What's the difference between deque and list STL containers?
What is the difference between the two? I mean the methods are all the same. So, for a user, they work identically.
Is that correct??
- 92.4k
111
votes
2
answers
91k
views
how to append a list<T> object to another
in C++, I have two list<T> objects A and B and I want to add all the members of B to the end of A. I've searched a few different sources and haven't found a simple solution (e.i. A.append(B);) ...
- 76.9k
105
votes
5
answers
326k
views
How to get a certain element in a list, given the position?
So I've got a list:
list<Object> myList;
myList.push_back(Object myObject);
I'm not sure but I'm confident that this would be the "0th" element in the array.
Is there any function I can use ...
- 1,051
86
votes
5
answers
65k
views
QVector vs QList
I have a list of integers that I need to iterate over but an array is inadequate.
What are the differences between vectors and lists and is there anything I need to know before I pick a type?
Just to ...
- 57k
82
votes
6
answers
298k
views
Pointer to incomplete class type is not allowed
For some reason I cannot use functions attached to the object I want to use. I added a comment to the line that is not working. As an error I get "Error; pointer to incomplete class type is not ...
- 3,142
68
votes
8
answers
28k
views
Is list::size() really O(n)?
Recently, I noticed some people mentioning that std::list::size() has a linear complexity.
According to some sources, this is in fact implementation dependent as the standard doesn't say what the ...
- 5,619
60
votes
3
answers
54k
views
How get next (previous) element in std::list without incrementing (decrementing) iterator?
Say I have an std::list<int> lst and some std::list<int>::iterator it for iterating through the list. And depended to value of the it I want to use it + 1 or it - 1 in my code. Is there ...
- 10.9k
55
votes
8
answers
94k
views
array vs vector vs list
I am maintaining a fixed-length table of 10 entries. Each item is a structure of like 4 fields. There will be insert, update and delete operations, specified by numeric position. I am wondering which ...
- 8,876
55
votes
2
answers
110k
views
How to initialize member-struct in initializer list of C++ class?
I have the following class definitions in c++:
struct Foo {
int x;
char array[24];
short* y;
};
class Bar {
Bar();
int x;
Foo foo;
};
and would like to initialize the "foo" struct (...
- 9,787
54
votes
5
answers
96k
views
How to make the for each loop function in C++ work with a custom class
I'm new to C/C++ programming, but I've been programming in C# for 1.5 years now. I like C# and I like the List class, so I thought about making a List class in C++ as an exercise.
List<int> ls;
...
- 2,653
51
votes
15
answers
100k
views
Cleaning up an STL list/vector of pointers
What is the shortest chunk of C++ you can come up with to safely clean up a std::vector or std::list of pointers? (assuming you have to call delete on the pointers?)
list<Foo*> foo_list;
I'd ...
- 17.1k
42
votes
3
answers
30k
views
Move list element to the end in STL
I have already the list pointer of CDrawObject*
std::list<CDrawObject*> elements;
How I can move some element to the end of list.
I see STL Algorithms Reference but i don't find this ...
- 3,666
42
votes
4
answers
209k
views
How to get an element at specified index from c++ List
I have a list:
list<Student>* l;
and I would like to get an element at a specified index. Example:
l->get(4)//getting 4th element
Is there a function or method in list which enables it ...
- 451
41
votes
5
answers
61k
views
How do you iterate backwards through an STL list?
I'm writing some cross-platform code between Windows and Mac.
If list::end() "returns an iterator that addresses the location succeeding the last element in a list" and can be checked when ...
- 4,682
40
votes
4
answers
34k
views
Why isn't there an operator[] for a std::list?
Can anyone explain why isn't the operator[] implemented for a std::list? I've searched around a bit but haven't found an answer. It wouldn't be too hard to implement or am I missing something?
- 9,667
39
votes
8
answers
55k
views
is there in C# a method for List<T> like resize in c++ for vector<T>
When I use resize(int newsize) in C++ for vector<T>, it means that the size of this vector are set to newsize and the indexes run in range [0..newsize). How to do the same in C# for List<T>...
- 1,549
35
votes
2
answers
36k
views
Using hierarchy in findContours () in OpenCV?
When finding contours, I used the CV_RETR_CCOMP argument. This is supposed to create a two level hierarchy - the the first level are for outer contours, the second level are for boundaries of the ...
- 5,316
32
votes
1
answer
6k
views
Complexity of std::list::splice and other list containers
I have some code which deals with various std::list objects, and I am currently using a very inefficient method of transferring content between them (I'm iterating through arbitrary sections of one ...
- 6,159
29
votes
8
answers
190k
views
How could I create a list in c++?
How can I create a list in C++? I need it to create a linked list. How would I go about doing that? Are there good tutorials or examples I could follow?
- 373
29
votes
6
answers
26k
views
Does std::list::remove method call destructor of each removed element?
I have the code:
std::list<Node *> lst;
//....
Node * node = /* get from somewhere pointer on my node */;
lst.remove(node);
Does the std::list::remove method call the destructor (and free ...
- 1,863
29
votes
3
answers
19k
views
Sort list using STL sort function
I'm trying to sort a list (part of a class) in descending order containing items of a struct, but it doesn't compile:
error: no match for 'operator-' in '__last - __first'
sort(Result.poly.begin(),...
- 618
27
votes
4
answers
18k
views
Pass, return and convert to vectors list of lists over JNI
I need to pass from Java
List< List<MyPoint> > points;
over jni to C++ and convert to
std::vector< std::vector<MyPoint> >
Process this vectors and return
List< List&...
- 949
25
votes
6
answers
40k
views
C++ STL list vs set
Which of those two is faster for random insertions and deletions?
My guess is list.
Though having the values as the keys as in the case of sets is attractive too.
Is performance similar for iterating ...
- 703
25
votes
6
answers
35k
views
How to access the 'previous' element in a C++ list iterator loop?
I'm trying to access the previously iterated element in a loop going through all the elements of a list.
To be more specific, my loop looks like this:
for (iter=list_object.begin(); iter!= ...
- 1,443
24
votes
3
answers
37k
views
Erasing while iterating an std::list
If I'm using an iterator in a for loop and I use erase on a current iteration of iterator, the for loop should continue fine and access the rest of the list elements?
From what I have read, this ...
- 24.4k
23
votes
2
answers
3k
views
Sorting a std::list using iterators
Is it possible to sort portion of a list (subset of a list) defined by iterators like std::sort does?
i.e with a std::list the only sort available is via a method (http://en.cppreference.com/w/cpp/...
- 1,047
22
votes
6
answers
45k
views
Python equivalent for C++ STL vector/list containers
Is there something similar in Python that I would use for a container that's like a vector and a list?
Any links would be helpful too.
- 5,495
22
votes
7
answers
5k
views
How to initialise a STL vector/list with a class without invoking the copy constructor
I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then ...
- 3,345
21
votes
5
answers
15k
views
How do I parallelize a for loop through a C++ std::list using OpenMP?
I would like to iterate through all elements in an std::list in parallel fashion using OpenMP. The loop should be able to alter the elements of the list. Is there a simple solution for this? It seems ...
- 965
20
votes
1
answer
14k
views
invalid operator < while sorting std::list
I have a std::list graph edges and i want to sort the edges based on their destination outdegree and then their indegree. But i am getting getting exception of invalid operator < during my ...
- 5,838
20
votes
5
answers
17k
views
Is there an equivalent of vector::reserve() for an std::list?
I have a class that looks like this:
typedef std::list<char*> PtrList;
class Foo
{
public:
void DoStuff();
private:
PtrList m_list;
PtrList::iterator m_it;
};
The function DoStuff() ...
- 32.8k
19
votes
2
answers
28k
views
sorting std::lists using std::sort [duplicate]
Possible Duplicate:
Sort list using stl sort function
My question is can we sort two std::lists using std::sort function? I have 2 string lists
std::list<std::string>list1, list2;
.....//...
- 3,344
19
votes
5
answers
24k
views
Memory leak with std::string when using std::list<std::string>
I'm working with std::list<std::string> in my current project. But there is a memory leak somewhere connected with this. So I've tested the problematic code separately:
#include <iostream>...
- 1,216
19
votes
6
answers
15k
views
Is returning a std::list costly?
I was wondering if returning a list, instead of returning a pointer to one, was costly in term of performance because if I recall, a list doesn't have a lot of attributes (isn't it something like 3 ...
- 9,667
19
votes
5
answers
28k
views
Python list equivalent in C++?
Could you please tell me what is the closest data type in C++ to python list? If there is nothing similar, how would you build it in C++?
- 9,740
19
votes
4
answers
67k
views
C++ pass list as a parameter to a function
I'm trying to build a very simple address book. I created a Contact class and the address book is a simple list. I'm trying to build a function to allow the user to add contacts to the address book. ...
- 609
18
votes
7
answers
43k
views
C++ STL: list with Pointers - Iterator cannot access?
I am struggeling with an STL list that holds Pointers of my "Object" object.
I declared:
list<Object*> objectlist;
and inserted via:
this->objectlist.push_back(new Object(address,value,...
- 2,593
17
votes
2
answers
2k
views
Why isn't std::list.size() constant-time? [duplicate]
This code ran for 0.012 seconds:
std::list<int> list;
list.resize(100);
int size;
for(int i = 0 ; i < 10000; i++)
size = list.size();
This one for 9.378 seconds:
std::list<int&...
- 193
16
votes
4
answers
45k
views
List Iterator Remove()
I have a list iterator that goes through a list and removes all the even numbers. I can use the list iterator to print out the numbers fine but I cannot use the list's remove() and pass in the ...
- 12.1k
16
votes
2
answers
1k
views
Use std::experimental::optional to implement a list
I was wondering if it is possible to implement a single (and possible double) linked list using std::experimental::optional.
template <typename T>
struct node {
std::experimental::optional&...
- 1,183
16
votes
6
answers
38k
views
Getting a list of values from a map
Is there an stl way to get a list of values from a map?
i.e, I have:
std::map<A,B> myMap;
and I would like a function that will return just the list of values, i.e, std::list<B> (or set ...
- 78k
16
votes
2
answers
35k
views
How to access the first element of std::list?
I have a list std::list<T *> *l;. this list is not null and has some values. My problem is how to access items properly? i do not need to iterate over the list. i just want the first item only.
...
- 1,164
15
votes
2
answers
26k
views
c++11 sorting list using lambda
While practicing the use of lambdas, I wrote this program which is supposed to sort a list of pairs by their second element (an int).
#include <iostream>
#include <algorithm>
#include <...
- 2,788
15
votes
1
answer
18k
views
Use nlohmann json to unpack list of integers to a std::vector<int>
I'm using nlohman::json.
It's awesome, but is there any way to unpack:
{
"my_list" : [1,2,3]
}
into a std:vector<int> ?
I can't find any mention in the docs, and std::vector<...
- 29.8k
15
votes
1
answer
1k
views
Using MMU to implement resizable arrays
Usually, lists are implemented either as linked lists, which are slow to traverse, or as array lists, which are slow when inserting elements.
I was wondering if it would be possible to use the ...
- 153
15
votes
1
answer
11k
views
Iterator equivalent to null pointer?
In an algorithm I'm currently implementing, I need to manipulate a std::list of struct T.
T holds a reference to another instance of T, but this reference can also be "unassigned".
At first, I wanted ...
- 893
15
votes
6
answers
4k
views
Cache-friendliness std::list vs std::vector
With CPU caches becoming better and better std::vector usually outperforms std::list even when it comes to testing the strengths of a std::list. For this reason, even for situations where I need to ...
- 36.1k
14
votes
1
answer
11k
views
How to handle list in R to Rcpp
I have a list in R that x<-list(c(1,2,3), c(4,5), c(5,5), c(6)). I want to input the list to Rcpp and return them as an average vector, c(2, 4.5, 5, 6).
I am not sure how to handle the list in ...
- 303