stdmap Questions
2
The "four basic kinds" of C++ sequence containers
(vector, forward_list, list, and deque)
all have an assign method. For example, std::vector has
(quoting cppreference.com):
void as...
2
Solved
I have two std::map<> objects a and b and would like to move (extract + insert) some elements (nodes) from one map to the other based on some predicate p.
for (auto i = a.begin(); i != a.end...
1
Solved
I just noticed that std::map and std::set have the member function equal_range() returning an iterator range of values for a certain key. How does this make sense when std::map and std::set a...
Garwin asked 1/5, 2024 at 8:36
3
Solved
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 i...
Revitalize asked 6/5, 2018 at 10:49
3
Solved
If there is a std::map<std::pair<std::string, std::string>, some_type> what is the best way to find its values?
I guess the most obvious one is to do something like this:
map.find(std::...
25
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This is one of the possible ways I come out:
struct RetrieveKey
{
template <typename T>
typename T::first_type operator()(T keyValuePair) const
{
return keyValuePair.first;
}
};
map<...
Hepburn asked 21/9, 2008 at 3:23
5
Solved
I tried to use the operator[] access the element in a const map, but this method failed. I also tried to use at() to do the same thing. It worked this time. However, I could not find any reference ...
Volkan asked 27/2, 2011 at 17:17
5
Solved
I'm trying to create a map inside a map:
typedef map<float,mytype> inner_map;
typedef map<float,inner_map> outer_map;
Will I be able to put something inside inner map, or does iterat...
5
I'm trying to use a std::string as a key in a std::map however, i'm unable to find() correctly. My code is somewhat complicated and large so this is a small program that demonstrates the problem I'...
3
Solved
I have a recurrent pattern with the use of std::map.
I want to retrieve the value only when the key is present, otherwise I don't want to insert element. Currently I'm using count(key) or find(key...
1
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The common advice is to prefer using std::map::try_emplace in preference to std::map::emplace in almost every instance.
I wrote a simple test to trace object creation/copying/moving/destruction whe...
6
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Since there is no .resize() member function in C++ std::map I was wondering, how one can get a std::map with at most n elements.
The obvious solution is to create a loop from 0 to n and use the nt...
15
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I'm trying to check if a given key is in a map and somewhat can't do it:
typedef map<string,string>::iterator mi;
map<string, string> m;
m.insert(make_pair("f","++--"));
pair<mi,mi&...
Ridgepole asked 21/12, 2009 at 12:55
6
Solved
I want to define something like
Map<int, char[5] > myMap;
The above declaration is accepted by c++ compiler and no error is thrown but when I do something like this
int main()
{
char arr...
Mcquillin asked 16/7, 2012 at 17:28
16
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Is there a way to specify the default value std::map's operator[] returns when an key does not exist?
1
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I noticed that the use of std::map::reverse_iterator in the below example doesn't work with C++20 but works with C++17 in all compilers.
Demo
Demo MSVC
#include <map>
class C; //incompl...
Snider asked 13/8, 2022 at 10:52
5
Solved
I want to inherit from std::map, but as far as I know std::map hasn't any virtual destructor.
Is it therefore possible to call std::map's destructor explicitly in my destructor to ensure proper o...
Shiksa asked 7/5, 2012 at 6:47
10
Solved
I am trying to figure out why the following code is not working, and I am assuming it is an issue with using char* as the key type, however I am not sure how I can resolve it or why it is occuring....
Bondman asked 11/11, 2010 at 18:4
6
Solved
I have the following shared_ptr to a map:
std::shared_ptr<std::map<double, std::string>>
and I would like to initialise it using braced-init. Is it possible?
I've tried:
std::strin...
Flagging asked 6/4, 2016 at 8:32
8
Solved
8
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I want to iterate through each element in the map<string, int> without knowing any of its string-int values or keys.
What I have so far:
void output(map<string, int> table)
{
map<...
Discophile asked 9/10, 2014 at 15:12
13
I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there either), but a quick search here doesn't seem to find it, so here it is:
Why does std::map...
Pharmacognosy asked 28/10, 2009 at 19:30
7
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What I mean is - we know that the std::map's elements are sorted according to the keys. So, let's say the keys are integers. If I iterate from std::map::begin() to std::map::end() using a for, does...
Vesuvian asked 4/10, 2011 at 13:35
8
I'm wondering why I can't use STL maps with user-defined classes. When I compile the code below, I get the following cryptic error message. What does it mean? Also, why is it only happening with us...
Grantinaid asked 9/7, 2009 at 7:42
5
Solved
I am looking for the highest key value (a defined by the comparison operator) of a std::map.
Is this guaranteed to be
map.rbegin()->first
?
(I am a bit shaky on reverse iterators, and how...
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