In C++, `std::set`s are a kind of associative container that stores unique elements, and in which the elements themselves are the keys.
Questions tagged [stdset]
294 questions
8
votes
3 answers
C++ std::set Find function overloading == operator
I am using sets. I use a custom struct as the key. I am inserting a value and trying to find the inserted value. But it never seems to find the element.
I have overridden both the == operator and the < operator.
Here is the code of the…
The Flying Dutchman
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7
votes
3 answers
C++ set search for pair element?
So I have a set of pairs
And I want to use find() to search for a single string which would be in the "first" of the pair, then if I find that string in first I want to return second from that function.
My current attempt…
user1288735
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7
votes
1 answer
How does std:set check if there is an equivalent element in set during the insertion?
Let's use the following code as an example.
auto cmp = [](ll a, ll b) {
return gcd(12, a) < gcd(12, b);
};
set s(cmp);
for(ll i = 0; i < 2; i++){
ll x;
cin >> x;
s.insert(x);
cout << "Success! \n";
}
I defined…
Shynggys Saparbek
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7
votes
5 answers
C++ equivalent of Python difference_update?
s1 and s2 are sets (Python set or C++ std::set)
To add the elements of s2 to s1 (set union), you can do
Python: s1.update(s2)
C++: s1.insert(s2.begin(), s2.end());
To remove the elements of s2 from s1 (set difference), you can do
Python:…
Johan Råde
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7
votes
2 answers
How to count the number of distinct values in a C++ std::map
I have a c++ map declared as follows
std::map wordMap= {
{ "is", 6 },
{ "the", 5 },
{ "hat", 9 },
{ "at", 6 }
};
I would like to know how to find the number of distinct values of int existing in wordMap.
In…
Pat. ANDRIA
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7
votes
2 answers
Storing in std::map/std::set vs sorting a vector after storing all data
Language: C++
One thing I can do is allocate a vector of size n and store all data
and then sort it using sort(begin(),end()). Else, I can keep putting
the data in a map or set which are ordered itself so I don't have to
sort afterwards. But in…
Indrajit Banerjee
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7
votes
3 answers
std::set find behavior with char * type
I have below code line:
const char *values[] = { "I", "We", "You", "We"};
std::set setValues;
for( int i = 0; i < 3; i++ ) {
const char *val = values[i];
std::set::iterator it = setValues.find( val );
if( it…
user987316
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7
votes
1 answer
For how long the iterator returned by std::set.find() lives?
I need to keep track of std::set element by saving the iterator returned by set.find().
My questions is does insertion and removing other elements invalidates the obtained iterator? From a simple test I did I can see it is not, but I'd like to…
jackhab
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7
votes
3 answers
How to elegantly put all enums into a std::set
I have an enum and I want to put them all in the set( and then remove some with set_intersection algorithm, but that is offtopic).
All works great except Im stuck on step 1. :)
If I have(real class has enum with higher cardinality)
class…
NoSenseEtAl
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6
votes
2 answers
How to use a std::set as a data member with an explicit comparator member function?
I am using C++17.
std::set is a template type:
template<
class Key,
class Compare = std::less,
class Allocator = std::allocator
> class set;
One can have a std::set as a data member. For example:
#include
class Foo
{
…
user1387866
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6
votes
3 answers
std::set won't compile
The const here is the cause of the compilation problem. However, having implemented an AVL tree myself, I can't understand why.
Here's the code:
#include
int main ()
{
int a;
// I want the set to carry the "promise"
// to…
Elliott
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6
votes
2 answers
Why cant items from std::set be 'popped'?
I know that std::set does not allow non-const access to it's items. I know that it's impossible to move items out of a the set – because any sort of non-const access might break the ordering of the set.
However, we CAN erase an item from the set.…
Thor Correia
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6
votes
2 answers
with custom struct contains duplicates
I've been learning c++. I am stuck with this problem.
I have set that contains a custom struct that contains two long int's a & b. I have a custom comparer struct that compares the numbers and returns true if either a or b is different.
typedef long…
Srikanth R
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6
votes
5 answers
How can I get a std::set of characters in a string, as strings?
I have a std::string. I want the set of unique characters in it, with each character represented as a std::string.
I can get the set of characters easily:
std::string some_string = ...
std::set char_set(some_string.begin(),…
EMBLEM
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6
votes
4 answers
Is it possible to use elements of a different type than contained in a std::set to perform search and deletion?
Let's say I have the following:
struct MetadataThingy {
void *actual_thingy;
int some_metadata;
int more_metadata;
bool operator<(MetadataThingy const& other) const {
return actual_thingy < other.actual_thingy;
…
jaymmer - Reinstate Monica
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