A std::pair is an ordered, heterogeneous sequence of exactly two objects (it is a special case of std::tuple).
std::pair is a part of the C++ Standard Library, defined in the header <utility>.
Questions tagged [std-pair]
776 questions
11
votes
1 answer
c++ - How to get first and second element of pair if used as key in map?
I was trying to get first and second element of pair when i am using pair as key in map.For better clarification please see code below.This is what i have tried
#include
using namespace std;
int main()
{
// your code goes…
chota bheem
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11
votes
4 answers
Accessing a pair after moving it into a map
If I move a pair into a map, but the insert failed because the key already exists, can I safely use the pair afterwards?
//objects available: map, pair
auto insert_pair = map.insert(std::move(pair));
if (!insert_pair.second)
{
//can I safely…
roger.james
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- 1
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10
votes
6 answers
Is there a standard C++ function object for taking apart a std::pair?
Does anyone know if there's a de-facto standard (i.e., TR1 or Boost) C++ function object for accessing the elements of a std::pair? Twice in the past 24 hours I've wished I had something like the keys function for Perl hashes. For example, it…
Michael Kristofik
- 34,290
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10
votes
4 answers
C++ Error Handling - downside of using std::pair or std::tuple for returning error codes and function returns
Without getting into the general exceptions vs error codes discussion, what do you think are the downsides of using std::pair or std:tuple for returning multiple values, namely the function's return value AND the error/success code, similar to how…
CodeSalad
- 1,375
- 2
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9
votes
5 answers
Is it possible to cast a pair to a pair?
So I have a smart iterator that emulates a map const_iterator, and it needs to build the return type internally. Obviously, I'd like to store a pair in my iterator class (since I need to modify it), but at the same time I'd like the…
masaers
- 697
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- 21
9
votes
3 answers
Correct friend definition to give std::map access to private default constructor
I am working on a library which uses a struct which should not have the default constructor accessible by users of the lib.
struct Example
{
Example(int x);
private:
Example();
};
Inside the library the the default constructor is…
Beginner
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9
votes
1 answer
Do std::tuple and std::pair support aggregate initialization?
Aggregate initialization requires among other things no user-provided constructors. But std::tuple and std::pair pair have a large set of overloaded constructors. From the point of the core language, are these constructors user-provided or even…
Johan Lundberg
- 26,184
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9
votes
2 answers
Changing value in a pair from foreach doesn't show change out of loop
I have an object outside of the for-each loops that contains a static vector of pair.
I want to increment the second parameter of the pair, as the code below shows. However, when I print the second parameter from within another for-each loop, it…
user3812584
- 103
- 1
- 5
9
votes
1 answer
How to std::hash an unordered std::pair
I want to be able to use a std::pair as a key in an unordered_container. I know that I could do this the following way:
template
void
hash_combine(std::size_t &seed, T const &key) {
std::hash hasher;
seed ^= hasher(key) +…
101010
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9
votes
3 answers
Problem with std::map and std::pair
I have a small program I want to execute to test something
#include
Tom
- 43,810
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9
votes
1 answer
Why can't you assign a pair from a tuple, but tuple can be assigned from a pair?
I'm not clear why it is legal to assign tuple=pair
But it is illegal to assign pair=tuple
std::pair x { 1 , 5.5};
std::tuple y { 1 , 5.5};
int a;
double b;
std::tie(a,b) = x;
…
Glenn Teitelbaum
- 10,108
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- 80
9
votes
4 answers
Will RVO happen when returning std::pair?
A function needs to return two values to the caller. What is the best way to implement?
Option 1:
pair myfunc()
{
...
return make_pair(getU(),getV());
}
pair mypair = myfunc();
Option 1.1:
// Same defn
U u; V v;
tie(u,v) =…
balki
- 26,394
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9
votes
4 answers
ISO C++ forbids declaration of ‘tuple’ with no type
When trying to compile a simple class (g++ myclass.cpp), I get the following error:
ISO C++ forbids declaration of ‘tuple’ with no type
I searched for this problem, and in most cases people seemed to forget std:: or including in the…
Jawap
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9
votes
1 answer
c2664 in Visual Studio 2012 when using make_pair
I dig up an old project and wanted to compile it, but received several errors, a few of those being a c2664:
error C2664: 'std::make_pair' : cannot convert parameter 1 from 'CUser *' to 'CUser *&&'
error C2664: 'std::make_pair' : cannot convert…
Juarrow
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- 61
8
votes
6 answers
How to declare a static lookup table using C++11
I have C++11 program which needs to pick a value from a range of values. Each of the ranges have an assigned value to pick a value from.
Following is my range of values with assigned values for each.
1-10 = 5
11-14 = 13
15-20 = 17
21-28 = 24
29-36 =…
AdeleGoldberg
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