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Alessandro

C++: std::find and erase in vector struct

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Hi, I have a std::vector that points to a structure, like this:


std::vector<myObjects::myObjectLib> myObject;



typedef struct {
float X,Y,Z;
int objID;
} myObjectLib ;


The myObject vector is already filled with data, and now I'd like to find and erase all the items where objID=1 (to make an example).
I know how to do it with a standard vector, but I don't know how to do it when the vector, like in this case, addresses a struct.
Thanks

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In this case you wouldn't use std::find(), you'd use std::find_if(). Create a predicate that will check the objID and pass it to the function.

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Thanks.
I created the predicate function like this:


bool checkObj (myObjects::myObjectLib temp) {
if (temp.objID==1) return true;
else return false;
}

and later


std::vector<int>::const_iterator it;
it = std::find_if (myObject.begin(), myObject.end(), checkObj(myObject)); //<- how do I pass the myObject vector?


I don't know how to pass the myObject vector to the predicate. And not sure if I made some more mistakes...

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Two small things:
1. Your predicate should take a constant reference (Although in this case the compiler would probably optimise both to the same assembly), so your function signature would be:
bool checkObj (const myObjects::myObjectLib& temp)

2. You don't pass the vector to the predicate directly, find_if() does that. So your find_if() call looks like:

it = std::find_if(myObject.begin(), myObject.end(), checkObj);

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You don't have to pass it yourself, find_if will do that automatically. Also you probably should use remove_if for "removal" operations since that will reduce copy operations.

[source lang="c++"]
struct HasId {
HasId(int i) : id(i) { }
bool operator()(const myObjects::myObjectLib &obj) { return obj.objID==id; }
int id;
};

//...

iterator new_end = remove_if(myObject.begin(), myObject.end(), HasId(1));
myObject.erase(new_end, myObject.end());
[/source]

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