Adding empty element to declared container without declaring type of element

When we use a complicated container in C++, like

std::vector<std::map<std::string, std::set<std::string>>> table;

The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with

table.push_back(std::map<std::string, std::set<std::string>>());

Is there any way to avoid redeclaring the type, and just adding the correct typed element?

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

add a comment |

When we use a complicated container in C++, like

std::vector<std::map<std::string, std::set<std::string>>> table;

The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with

table.push_back(std::map<std::string, std::set<std::string>>());

Is there any way to avoid redeclaring the type, and just adding the correct typed element?

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

add a comment |

When we use a complicated container in C++, like

std::vector<std::map<std::string, std::set<std::string>>> table;

The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with

table.push_back(std::map<std::string, std::set<std::string>>());

Is there any way to avoid redeclaring the type, and just adding the correct typed element?

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

When we use a complicated container in C++, like

std::vector<std::map<std::string, std::set<std::string>>> table;

The only way to add an empty map (which may represent a row or column) is to initialize a new element and push it back. For example with

table.push_back(std::map<std::string, std::set<std::string>>());

Is there any way to avoid redeclaring the type, and just adding the correct typed element?

c++ c++11

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

edited Mar 25 at 10:41

Mohammad Usman

21.4k134758

asked Mar 25 at 6:35

Vineet

354411

asked Mar 25 at 6:35

Vineet

354411

asked Mar 25 at 6:35

Vineet

354411

add a comment |

5 Answers
5

active

oldest

votes

From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.

table.emplace_back();

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

add a comment |

You can take advantage of copy-list-initialization (since C++11) and just write

table.push_back({});

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

add a comment |

Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).

answered Mar 25 at 6:49

6502

87.6k13115218

add a comment |

Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.

I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!

 using PhilosopherNameType = std::string;

 using NeighboursType      = std::set<PhilosopherNameType>;

 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;



 std::vector<NeighbourMapType> table;

 table.push_back(NeighbourMapType());

I mention this because you can likely still benefit from this in other places.

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

2

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

add a comment |

As a example:

    vector<int> arr;

    arr.push_back(1);

    arr.push_back(2);

To use it, you should:

include

and also, either use std::vector in your code or add

using std::vector;

using namespace std;

after the #include line.

answered yesterday

Mr. Semicolon

5301422

add a comment |

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5 Answers
5

active

oldest

votes

5 Answers
5

active

oldest

votes

From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.

table.emplace_back();

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

add a comment |

From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.

table.emplace_back();

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

add a comment |

From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.

table.emplace_back();

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

From CLion's IntelliSense, I later found that one useful method is emplace_back(). This constructs a new object of correct type and adds it to the end of the vector.

table.emplace_back();

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

edited Mar 25 at 7:12

answered Mar 25 at 6:51

Vineet

354411

answered Mar 25 at 6:51

Vineet

354411

answered Mar 25 at 6:51

Vineet

354411

add a comment |

You can take advantage of copy-list-initialization (since C++11) and just write

table.push_back({});

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

add a comment |

You can take advantage of copy-list-initialization (since C++11) and just write

table.push_back({});

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

add a comment |

You can take advantage of copy-list-initialization (since C++11) and just write

table.push_back({});

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

You can take advantage of copy-list-initialization (since C++11) and just write

table.push_back({});

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

edited Mar 25 at 6:46

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

answered Mar 25 at 6:37

songyuanyao

93.8k11182249

add a comment |

Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).

answered Mar 25 at 6:49

6502

87.6k13115218

add a comment |

Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).

answered Mar 25 at 6:49

6502

87.6k13115218

add a comment |

Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).

answered Mar 25 at 6:49

6502

87.6k13115218

Before C++11 sometimes I use x.resize(x.size()+1), in C++11 or later you can use x.push_back({}).

answered Mar 25 at 6:49

6502

87.6k13115218

answered Mar 25 at 6:49

6502

87.6k13115218

answered Mar 25 at 6:49

6502

87.6k13115218

answered Mar 25 at 6:49

6502

87.6k13115218

add a comment |

Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.

I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!

 using PhilosopherNameType = std::string;

 using NeighboursType      = std::set<PhilosopherNameType>;

 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;



 std::vector<NeighbourMapType> table;

 table.push_back(NeighbourMapType());

I mention this because you can likely still benefit from this in other places.

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

2

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

add a comment |

Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.

I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!

 using PhilosopherNameType = std::string;

 using NeighboursType      = std::set<PhilosopherNameType>;

 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;



 std::vector<NeighbourMapType> table;

 table.push_back(NeighbourMapType());

I mention this because you can likely still benefit from this in other places.

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

2

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

add a comment |

Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.

I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!

 using PhilosopherNameType = std::string;

 using NeighboursType      = std::set<PhilosopherNameType>;

 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;



 std::vector<NeighbourMapType> table;

 table.push_back(NeighbourMapType());

I mention this because you can likely still benefit from this in other places.

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

Though the other answers are correct, I will add that if you couldn't take that approach, you could have benefitted from declaring some type aliases to shorten that container type name.

I can of course only guess at the logical meaning of your containers, which is another thing that this fixes!

 using PhilosopherNameType = std::string;

 using NeighboursType      = std::set<PhilosopherNameType>;

 using NeighbourMapType    = std::map<PhilosopherNameType, NeighboursType>;



 std::vector<NeighbourMapType> table;

 table.push_back(NeighbourMapType());

I mention this because you can likely still benefit from this in other places.

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

answered Mar 25 at 17:12

Lightness Races in Orbit

294k54477811

2

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

add a comment |

2

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

agreed. Along the same lines are the types that the STL gives you (vector::value_type iirc)

– sudo rm -rf slash
Mar 26 at 8:01

add a comment |

As a example:

    vector<int> arr;

    arr.push_back(1);

    arr.push_back(2);

To use it, you should:

include

and also, either use std::vector in your code or add

using std::vector;

using namespace std;

after the #include line.

answered yesterday

Mr. Semicolon

5301422

add a comment |

As a example:

    vector<int> arr;

    arr.push_back(1);

    arr.push_back(2);

To use it, you should:

include

and also, either use std::vector in your code or add

using std::vector;

using namespace std;

after the #include line.

answered yesterday

Mr. Semicolon

5301422

add a comment |

As a example:

    vector<int> arr;

    arr.push_back(1);

    arr.push_back(2);

To use it, you should:

include

and also, either use std::vector in your code or add

using std::vector;

using namespace std;

after the #include line.

answered yesterday

Mr. Semicolon

5301422

As a example:

    vector<int> arr;

    arr.push_back(1);

    arr.push_back(2);

To use it, you should:

include

and also, either use std::vector in your code or add

using std::vector;

using namespace std;

after the #include line.

answered yesterday

Mr. Semicolon

5301422

answered yesterday

Mr. Semicolon

5301422

answered yesterday

Mr. Semicolon

5301422

answered yesterday

Mr. Semicolon

5301422

add a comment |

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