You can certainly do this if you want to, but there doesn't seem to be any logical reason. The compiler doesn't complain because this doesn't modify data
(which is a pointer) but rather the thing data
points to, which is perfectly legal to do with a const
pointer.
Operating on dynamic memory, is it meaningful to overload a const memeber function?
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20-09-2022 - |
Question
An exercise from C++ Primer 5 Edition made me stuck, which goes like
Exercise 12.3: Does this class need const versions of push_back and pop_back? If so, add them. If not, why aren’t they needed? (Page 458)
Below is the class. Definitions for members front
and back
are omitted to simplify the codes.
class StrBlob
{
public:
typedef std::vector<std::string>::size_type size_type;
StrBlob();
StrBlob(std::initializer_list<std::string> il);
size_type size() const { return data->size(); }
bool empty() const { return data->empty(); }
// add and remove elements
void push_back(const std::string &t) {data->push_back(t);}
void pop_back();
// element access
std::string& front();
std::string& back();
private:
std::shared_ptr<std::vector<std::string>> data;
// throws msg if data[i] isn't valid
void check(size_type i, const std::string &msg) const;
};
StrBlob::StrBlob(): data(make_shared<vector<string>>()) { }
StrBlob::StrBlob(initializer_list<string> il):
data(make_shared<vector<string>>(il)) { }
void StrBlob::check(size_type i, const string &msg) const
{
if (i >= data->size())
throw out_of_range(msg);
}
void StrBlob::pop_back()
{
check(0, "pop_back on empty StrBlob");
data->pop_back();
}
I tried to overload a const member void StrBlob::pop_back() const
as below.
void StrBlob::pop_back() const
{
check(0, "pop_back on empty wy_StrBlob");
data->pop_back();
}
Compiler complained nothing about this const member. wondering am I doing right? Is there any possibility that this const member can be called? Is it meaningful to add this const member? Why?
Solution
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