CODEWITHSUNDEEP
c++vector
user997112
user997112

Reputation: 30615

C++ std::vector remove MyClass object

If I have a std::vector and at some point through the code I add an instance of a MyClass object, later on how can I remove THAT particular object from the vector?

(I found a question on SO which explained how to remove ints, but they are primitive and I dont know if the same technique would work with user-defined classes)

std::vector<MyClass> v;
MyClass m;
v.push_back(m);
.
.
.
//Wish to remove m from v??

EDIT: You do not know the position of m in the vector.

Upvotes: 0

Views: 1314

Answers (3)

111111
111111

Reputation: 16148

if you know it is still the last element:

v.pop_back();

Else

auto it=std::find(begin(v),end(v),m);
if(it!=end(v)) v.erase(it);

Note, that push_back duplicates m via it's copy ctor, it is not the same m as in the code that calls push_back it just has the same value (unlike say Java semantics).

EDIT:

op== and op< can be implemented like so.

struct s {
    std::string name;
    int id;
};

bool operator==(const s& l, const s& r) {
    return l.id   == r.id
    &&     l.name == r.name
    ;
}

bool operator<(const s& l, const s& r) {
     return std::make_tuple(l.id, l.name)
     <      std::make_tuple(r.id, r.name)
     ;
}

Upvotes: 3

Eugene
Eugene

Reputation: 9474

C++11:

std::vector<int> v = {1,2,3,4,5};
auto end = std::remove(v.begin(), v.end(), 3);
v.resize(end - v.begin());

Upvotes: 0

juanchopanza
juanchopanza

Reputation: 227390

You have to be aware that the vector stores its own copy of m. So you need to define a criteria for something that is equivalent to m. Then you can use std::find or std::find_if to get an iterator to the first equivalent instance, and call std::vector::erase to remove it.

Assuming equivalenve is defined via an operator==(const MyClass&, const MyClass&), then

auto it = std::find(v.begin(), v.end(), m);
if(it != v.end()) 
  v.erase(it);

To use other criteria:

bool eq(const MyClass& lhs, const MyClass& rhs) { .... }
auto it = std::find_if(v.begin(), v.end(), eq);
if(it != v.end()) 
  v.erase(it);

Here, eq could be replaced by a functor instance or a lambda expression.

Upvotes: 2

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