[英]std::find on a vector of object pointers
I have a class A
with a member which is a vector of object pointers of another class B
我有一个成员为
A
的类,该成员是另一个B
的对象指针的向量
class A
{
std::vector<B*> m_member_A
Now I want to perform a std::find
on m_member_A
. 现在我想在
m_member_A
上执行一个std::find
。 Eg if(std::find(m_member_A.begin(), m_member_A.end(), B_obj*) != m_member_A.end())
例如
if(std::find(m_member_A.begin(), m_member_A.end(), B_obj*) != m_member_A.end())
std::find doesn't make sense on such a vector. std :: find在这样的向量上没有意义。 How do I achieve such a functionality?
我如何实现这种功能?
How would it change if it were a vector of objects of B (not pointer)? 如果它是B对象(不是指针)的向量,它将如何改变?
Vector works perfectly fine with std::find
Vector与
std::find
完美配合
auto result = std::find(m_member_A.begin(), m_member_A.end(), itemToFind);
if (result != m_member_A.end()) {
// found it!
}
Or if you need to dereference the pointer: 或者,如果您需要取消引用指针:
auto result = std::find_if(m_member_A.begin(), m_member_A.end(),
[] (B* item) {
if (item == nullptr) return false; // may want to do something else here
return *item == someValue;
});
if (result != m_member_A.end()) {
// found it!
}
Demo: http://ideone.com/jKCrG5 演示: http : //ideone.com/jKCrG5
If you want to find a value pointer at by the pointer, instead of a given pointer, you can use std::find_if
with a suitable functor: 如果要在指针
std::find_if
找到一个值指针,而不是给定指针,则可以将std::find_if
与合适的函子一起使用:
struct Foo
{
int i;
};
bool operator==(const Foo& lhs, const Foo& rhs) { return lhs.i == rhs.i; }
std::vector<Foo*> v = ....;
Foo f{42};
std::find_if(v.begin(), v.end(), [&f](const Foo* p) { return *p == f; });
If you want to compare values instead of comparing pointers, you might want to use std::find_if instead: 如果要比较值而不是比较指针,则可能要使用std :: find_if代替:
bool IsFoo (B* _item) {
bool result = false;
if ( _item != nullptr && _item->value == 1 ) //Whatever is your criteria
result = true;
return result;
}
std::vector<B*> m_member_A;
B* instance = std::find_if (m_member_A.begin(), m_member_A.end(), IsFoo);
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