Object initialization in C++
I am looking at someone's code, I don't understand how the object getting initialized here:
template <typename String>
void test_numbers()
{
SampleClass<String> compare;
String lhs = "abc";
String rhs = "efg";
check_equality(compare(lhs, rhs), true);
}
The object compare is created of class type SampleClass and then assigned 2 strings when passed on as a parameter. How this initialization works? Any comments? suggestions?
c++ class templates object
edited Nov 21 at 2:40
Cœur
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
add a comment |
I am looking at someone's code, I don't understand how the object getting initialized here:
template <typename String>
void test_numbers()
{
SampleClass<String> compare;
String lhs = "abc";
String rhs = "efg";
check_equality(compare(lhs, rhs), true);
}
The object compare is created of class type SampleClass and then assigned 2 strings when passed on as a parameter. How this initialization works? Any comments? suggestions?
c++ class templates object
edited Nov 21 at 2:40
Cœur
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
Which initialization?
– kennytm
Feb 23 '12 at 19:32
4
That depends on the definition ofSampleClasswhich you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.
– AJG85
Feb 23 '12 at 19:33
add a comment |
I am looking at someone's code, I don't understand how the object getting initialized here:
template <typename String>
void test_numbers()
{
SampleClass<String> compare;
String lhs = "abc";
String rhs = "efg";
check_equality(compare(lhs, rhs), true);
}
The object compare is created of class type SampleClass and then assigned 2 strings when passed on as a parameter. How this initialization works? Any comments? suggestions?
c++ class templates object
edited Nov 21 at 2:40
Cœur
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
I am looking at someone's code, I don't understand how the object getting initialized here:
template <typename String>
void test_numbers()
{
SampleClass<String> compare;
String lhs = "abc";
String rhs = "efg";
check_equality(compare(lhs, rhs), true);
}
The object compare is created of class type SampleClass and then assigned 2 strings when passed on as a parameter. How this initialization works? Any comments? suggestions?
c++ class templates object
c++ class templates object
edited Nov 21 at 2:40
Cœur
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
edited Nov 21 at 2:40
Cœur
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
edited Nov 21 at 2:40
Cœur
17.4k9102143
edited Nov 21 at 2:40
Cœur
17.4k9102143
edited Nov 21 at 2:40
Cœur
17.4k9102143
17.4k9102143
asked Feb 23 '12 at 19:29
RAB
409
asked Feb 23 '12 at 19:29
RAB
409
asked Feb 23 '12 at 19:29
RAB
409
409
Which initialization?
– kennytm
Feb 23 '12 at 19:32
4
That depends on the definition ofSampleClasswhich you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.
– AJG85
Feb 23 '12 at 19:33
add a comment |
Which initialization?
– kennytm
Feb 23 '12 at 19:32
4
That depends on the definition ofSampleClasswhich you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.
– AJG85
Feb 23 '12 at 19:33
Which initialization?
– kennytm
Feb 23 '12 at 19:32
Which initialization?
– kennytm
Feb 23 '12 at 19:32
4
4
That depends on the definition of
SampleClass which you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.– AJG85
Feb 23 '12 at 19:33
That depends on the definition of
SampleClass which you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.– AJG85
Feb 23 '12 at 19:33
add a comment |
2 Answers
2
active
oldest
votes
//I am initialised with my default constructor (no args)
SampleClass<String> compare;
//I am initialised with my `const char*` constructor (and assignment operator)
String lhs = "abc";
String rhs = "efg";
//Compare (already initialised) is being invoked by it's `operator()`
check_equality(compare(lhs, rhs), true);
compare is already constructed. It has an operator() implemented that allows it to appear as a function, accepting arguments.
you can make your own easily.
struct op_test{
int i;
op_test(int i_) : i(i_){}
int operator()(int j)const { return j*i; }
};
:::
op_test ot(5);
ot(6); //5*6
The reason this is useful is because we can do thing like this.
std::vector<int> a(700); //700 ints
std::transform(a.begin(), a.end(), b.begin(), op_test(5));
//or
std::transform(a.begin(), a.end(), b.begin(), &my_func); //calls a function
std::transform(a.begin(), a.end(), b.begin(), (int i){ return i*5; }); //lambda
see here:
http://msdn.microsoft.com/en-us/library/5tk49fh2(v=vs.80).aspx
useful with
http://en.cppreference.com/w/cpp/algorithm
answered Feb 23 '12 at 19:32
111111
11.8k43153
"//Compare (already initialised) is being invoked by it'soperator()" Can you please elaborate on this? thanks!
– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
add a comment |
It simply creates an automatic variable of type SampleClass<String>. Then its operator() is called with two String arguments.
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
//I am initialised with my default constructor (no args)
SampleClass<String> compare;
//I am initialised with my `const char*` constructor (and assignment operator)
String lhs = "abc";
String rhs = "efg";
//Compare (already initialised) is being invoked by it's `operator()`
check_equality(compare(lhs, rhs), true);
compare is already constructed. It has an operator() implemented that allows it to appear as a function, accepting arguments.
you can make your own easily.
struct op_test{
int i;
op_test(int i_) : i(i_){}
int operator()(int j)const { return j*i; }
};
:::
op_test ot(5);
ot(6); //5*6
The reason this is useful is because we can do thing like this.
std::vector<int> a(700); //700 ints
std::transform(a.begin(), a.end(), b.begin(), op_test(5));
//or
std::transform(a.begin(), a.end(), b.begin(), &my_func); //calls a function
std::transform(a.begin(), a.end(), b.begin(), (int i){ return i*5; }); //lambda
see here:
http://msdn.microsoft.com/en-us/library/5tk49fh2(v=vs.80).aspx
useful with
http://en.cppreference.com/w/cpp/algorithm
answered Feb 23 '12 at 19:32
111111
11.8k43153
"//Compare (already initialised) is being invoked by it'soperator()" Can you please elaborate on this? thanks!
– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
add a comment |
//I am initialised with my default constructor (no args)
SampleClass<String> compare;
//I am initialised with my `const char*` constructor (and assignment operator)
String lhs = "abc";
String rhs = "efg";
//Compare (already initialised) is being invoked by it's `operator()`
check_equality(compare(lhs, rhs), true);
compare is already constructed. It has an operator() implemented that allows it to appear as a function, accepting arguments.
you can make your own easily.
struct op_test{
int i;
op_test(int i_) : i(i_){}
int operator()(int j)const { return j*i; }
};
:::
op_test ot(5);
ot(6); //5*6
The reason this is useful is because we can do thing like this.
std::vector<int> a(700); //700 ints
std::transform(a.begin(), a.end(), b.begin(), op_test(5));
//or
std::transform(a.begin(), a.end(), b.begin(), &my_func); //calls a function
std::transform(a.begin(), a.end(), b.begin(), (int i){ return i*5; }); //lambda
see here:
http://msdn.microsoft.com/en-us/library/5tk49fh2(v=vs.80).aspx
useful with
http://en.cppreference.com/w/cpp/algorithm
answered Feb 23 '12 at 19:32
111111
11.8k43153
"//Compare (already initialised) is being invoked by it'soperator()" Can you please elaborate on this? thanks!
– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
add a comment |
//I am initialised with my default constructor (no args)
SampleClass<String> compare;
//I am initialised with my `const char*` constructor (and assignment operator)
String lhs = "abc";
String rhs = "efg";
//Compare (already initialised) is being invoked by it's `operator()`
check_equality(compare(lhs, rhs), true);
compare is already constructed. It has an operator() implemented that allows it to appear as a function, accepting arguments.
you can make your own easily.
struct op_test{
int i;
op_test(int i_) : i(i_){}
int operator()(int j)const { return j*i; }
};
:::
op_test ot(5);
ot(6); //5*6
The reason this is useful is because we can do thing like this.
std::vector<int> a(700); //700 ints
std::transform(a.begin(), a.end(), b.begin(), op_test(5));
//or
std::transform(a.begin(), a.end(), b.begin(), &my_func); //calls a function
std::transform(a.begin(), a.end(), b.begin(), (int i){ return i*5; }); //lambda
see here:
http://msdn.microsoft.com/en-us/library/5tk49fh2(v=vs.80).aspx
useful with
http://en.cppreference.com/w/cpp/algorithm
answered Feb 23 '12 at 19:32
111111
11.8k43153
//I am initialised with my default constructor (no args)
SampleClass<String> compare;
//I am initialised with my `const char*` constructor (and assignment operator)
String lhs = "abc";
String rhs = "efg";
//Compare (already initialised) is being invoked by it's `operator()`
check_equality(compare(lhs, rhs), true);
compare is already constructed. It has an operator() implemented that allows it to appear as a function, accepting arguments.
you can make your own easily.
struct op_test{
int i;
op_test(int i_) : i(i_){}
int operator()(int j)const { return j*i; }
};
:::
op_test ot(5);
ot(6); //5*6
The reason this is useful is because we can do thing like this.
std::vector<int> a(700); //700 ints
std::transform(a.begin(), a.end(), b.begin(), op_test(5));
//or
std::transform(a.begin(), a.end(), b.begin(), &my_func); //calls a function
std::transform(a.begin(), a.end(), b.begin(), (int i){ return i*5; }); //lambda
see here:
http://msdn.microsoft.com/en-us/library/5tk49fh2(v=vs.80).aspx
useful with
http://en.cppreference.com/w/cpp/algorithm
answered Feb 23 '12 at 19:32
111111
11.8k43153
edited Feb 23 '12 at 19:37
answered Feb 23 '12 at 19:32
111111
11.8k43153
answered Feb 23 '12 at 19:32
111111
11.8k43153
answered Feb 23 '12 at 19:32
111111
11.8k43153
11.8k43153
"//Compare (already initialised) is being invoked by it'soperator()" Can you please elaborate on this? thanks!
– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
add a comment |
"//Compare (already initialised) is being invoked by it'soperator()" Can you please elaborate on this? thanks!
– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
"//Compare (already initialised) is being invoked by it's
operator()" Can you please elaborate on this? thanks!– RAB
Feb 23 '12 at 19:34
"//Compare (already initialised) is being invoked by it's
operator()" Can you please elaborate on this? thanks!– RAB
Feb 23 '12 at 19:34
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
thank you very much, it solved my headache :)
– RAB
Feb 23 '12 at 19:39
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
I am glad I could be of service.
– 111111
Feb 23 '12 at 19:40
add a comment |
It simply creates an automatic variable of type SampleClass<String>. Then its operator() is called with two String arguments.
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
add a comment |
It simply creates an automatic variable of type SampleClass<String>. Then its operator() is called with two String arguments.
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
add a comment |
It simply creates an automatic variable of type SampleClass<String>. Then its operator() is called with two String arguments.
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
It simply creates an automatic variable of type SampleClass<String>. Then its operator() is called with two String arguments.
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
answered Feb 23 '12 at 19:33
Cat Plus Plus
89.8k22166201
89.8k22166201
add a comment |
add a comment |
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Which initialization?
– kennytm
Feb 23 '12 at 19:32
4
That depends on the definition of
SampleClasswhich you haven't shown. I suspect it is a function object which is poorly named or this is not the actual code you are looking at.– AJG85
Feb 23 '12 at 19:33