Is there any difference between the following commands from std::unordered_map
For inserting a key-value pair into an unordered map, e.g., std::unordered_pair<int,int> map1, can we do it in any of these two ways:
map1[2]=5;
map1.insert({2,5});
Is there any difference between using std_unordered_insert or operator?
And if I want to find the mapped value for a given key, can I use either of the following:
mappedVal = map1.at(2);
mappedVal = map1[2];
Again, any difference between using std::unordered_map::at or operator?
c++ stl insert unordered-map
asked Nov 12 '18 at 1:07
Iamanon
967
add a comment |
For inserting a key-value pair into an unordered map, e.g., std::unordered_pair<int,int> map1, can we do it in any of these two ways:
map1[2]=5;
map1.insert({2,5});
Is there any difference between using std_unordered_insert or operator?
And if I want to find the mapped value for a given key, can I use either of the following:
mappedVal = map1.at(2);
mappedVal = map1[2];
Again, any difference between using std::unordered_map::at or operator?
c++ stl insert unordered-map
asked Nov 12 '18 at 1:07
Iamanon
967
add a comment |
For inserting a key-value pair into an unordered map, e.g., std::unordered_pair<int,int> map1, can we do it in any of these two ways:
map1[2]=5;
map1.insert({2,5});
Is there any difference between using std_unordered_insert or operator?
And if I want to find the mapped value for a given key, can I use either of the following:
mappedVal = map1.at(2);
mappedVal = map1[2];
Again, any difference between using std::unordered_map::at or operator?
c++ stl insert unordered-map
asked Nov 12 '18 at 1:07
Iamanon
967
For inserting a key-value pair into an unordered map, e.g., std::unordered_pair<int,int> map1, can we do it in any of these two ways:
map1[2]=5;
map1.insert({2,5});
Is there any difference between using std_unordered_insert or operator?
And if I want to find the mapped value for a given key, can I use either of the following:
mappedVal = map1.at(2);
mappedVal = map1[2];
Again, any difference between using std::unordered_map::at or operator?
c++ stl insert unordered-map
c++ stl insert unordered-map
asked Nov 12 '18 at 1:07
Iamanon
967
asked Nov 12 '18 at 1:07
Iamanon
967
edited Nov 12 '18 at 2:15
asked Nov 12 '18 at 1:07
Iamanon
967
asked Nov 12 '18 at 1:07
Iamanon
967
asked Nov 12 '18 at 1:07
Iamanon
967
967
add a comment |
add a comment |
2 Answers
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map1[2]=5;
If an entry with key 2 exists, set that entry's value to 5. Otherwise, create a new entry with key 2 and value 5.
map1.insert({2,5});
If no entry with key 2 exists, create a new entry with key 2 and value 5. Otherwise, do nothing.
mappedVal = map1.at(2);
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, throw an out_of_range exception.
mappedVal = map1[2];
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, create an entry for 2 using the default value and assign that default value to mappedVal.
For lookups, I usually use unordered_map::find() rather than at() or operator () (unless I know that there is an entry for the given key).
answered Nov 12 '18 at 2:05
Sid S
3,5582723
add a comment |
In contrast to operator, at() will throw a std::out_of_range exception if the key doesn't exist. operator will create the key instead.
answered Nov 12 '18 at 1:10
Swordfish
1
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to useat()?
– Iamanon
Nov 12 '18 at 1:17
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
add a comment |
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2 Answers
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2 Answers
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map1[2]=5;
If an entry with key 2 exists, set that entry's value to 5. Otherwise, create a new entry with key 2 and value 5.
map1.insert({2,5});
If no entry with key 2 exists, create a new entry with key 2 and value 5. Otherwise, do nothing.
mappedVal = map1.at(2);
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, throw an out_of_range exception.
mappedVal = map1[2];
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, create an entry for 2 using the default value and assign that default value to mappedVal.
For lookups, I usually use unordered_map::find() rather than at() or operator () (unless I know that there is an entry for the given key).
answered Nov 12 '18 at 2:05
Sid S
3,5582723
add a comment |
map1[2]=5;
If an entry with key 2 exists, set that entry's value to 5. Otherwise, create a new entry with key 2 and value 5.
map1.insert({2,5});
If no entry with key 2 exists, create a new entry with key 2 and value 5. Otherwise, do nothing.
mappedVal = map1.at(2);
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, throw an out_of_range exception.
mappedVal = map1[2];
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, create an entry for 2 using the default value and assign that default value to mappedVal.
For lookups, I usually use unordered_map::find() rather than at() or operator () (unless I know that there is an entry for the given key).
answered Nov 12 '18 at 2:05
Sid S
3,5582723
add a comment |
map1[2]=5;
If an entry with key 2 exists, set that entry's value to 5. Otherwise, create a new entry with key 2 and value 5.
map1.insert({2,5});
If no entry with key 2 exists, create a new entry with key 2 and value 5. Otherwise, do nothing.
mappedVal = map1.at(2);
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, throw an out_of_range exception.
mappedVal = map1[2];
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, create an entry for 2 using the default value and assign that default value to mappedVal.
For lookups, I usually use unordered_map::find() rather than at() or operator () (unless I know that there is an entry for the given key).
answered Nov 12 '18 at 2:05
Sid S
3,5582723
map1[2]=5;
If an entry with key 2 exists, set that entry's value to 5. Otherwise, create a new entry with key 2 and value 5.
map1.insert({2,5});
If no entry with key 2 exists, create a new entry with key 2 and value 5. Otherwise, do nothing.
mappedVal = map1.at(2);
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, throw an out_of_range exception.
mappedVal = map1[2];
If an entry with key 2 exists, assign its value to mappedVal. Otherwise, create an entry for 2 using the default value and assign that default value to mappedVal.
For lookups, I usually use unordered_map::find() rather than at() or operator () (unless I know that there is an entry for the given key).
answered Nov 12 '18 at 2:05
Sid S
3,5582723
edited Nov 12 '18 at 2:34
answered Nov 12 '18 at 2:05
Sid S
3,5582723
answered Nov 12 '18 at 2:05
Sid S
3,5582723
answered Nov 12 '18 at 2:05
Sid S
3,5582723
3,5582723
add a comment |
add a comment |
In contrast to operator, at() will throw a std::out_of_range exception if the key doesn't exist. operator will create the key instead.
answered Nov 12 '18 at 1:10
Swordfish
1
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to useat()?
– Iamanon
Nov 12 '18 at 1:17
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
add a comment |
In contrast to operator, at() will throw a std::out_of_range exception if the key doesn't exist. operator will create the key instead.
answered Nov 12 '18 at 1:10
Swordfish
1
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to useat()?
– Iamanon
Nov 12 '18 at 1:17
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
add a comment |
In contrast to operator, at() will throw a std::out_of_range exception if the key doesn't exist. operator will create the key instead.
answered Nov 12 '18 at 1:10
Swordfish
1
In contrast to operator, at() will throw a std::out_of_range exception if the key doesn't exist. operator will create the key instead.
answered Nov 12 '18 at 1:10
Swordfish
1
answered Nov 12 '18 at 1:10
Swordfish
1
answered Nov 12 '18 at 1:10
Swordfish
1
answered Nov 12 '18 at 1:10
Swordfish
1
1
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to useat()?
– Iamanon
Nov 12 '18 at 1:17
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
add a comment |
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to useat()?
– Iamanon
Nov 12 '18 at 1:17
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to use
at()?– Iamanon
Nov 12 '18 at 1:17
Thanks. So I take this to mean that if I want to find the value at what I "think" is an existing key, then it would be safer to use
at()?– Iamanon
Nov 12 '18 at 1:17
1
1
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
@lamanon Sir, yes, Sir!
– Swordfish
Nov 12 '18 at 1:20
add a comment |
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