a sizeof problem about template

[hudaiqian]

hi,all I encounter a problem with sizeof

template <typename type>
void display(type& a)
{
cout<<sizeof(type)<<":"<<a[0]<<endl;
}

int main()
{
int a[6] = {1,2,3,4,5,6};
display(a);
}

the output is 24:1, its means is sizeof(type) equals 24,but the type
here is int
24 is the sizeof array a,why?Thanks

 

[Rolf Magnus]

hi,all I encounter a problem with sizeof

template <typename type>
void display(type& a)
{
cout<<sizeof(type)<<":"<<a[0]<<endl;
}

int main()
{
int a[6] = {1,2,3,4,5,6};
display(a);
}

the output is 24:1, its means is sizeof(type) equals 24,but the type
here is int

No, it's array[6] of int.

24 is the sizeof array a,why?Thanks

You pass an array to display, which expects a reference to some type. So you
are getting a reference to the array. Within display, 'type' is the type of
that array.

 

[Frederick Gotham]

(e-mail address removed) posted:

hi,all I encounter a problem with sizeof

template <typename type>
void display(type& a)
{
cout<<sizeof(type)<<":"<<a[0]<<endl;
}

int main()
{
int a[6] = {1,2,3,4,5,6};
display(a);
}

the output is 24:1, its means is sizeof(type) equals 24,but the type
here is int
24 is the sizeof array a,why?Thanks

"type" is int[6], not int.

Two remedies:

(1) Use: sizeof *a

or:

(2) Change the template to the following:

#include <cstddef>
#include <iostream>

template<class T,std::size_t len>
void Display(T const (&arr)[len])
{
std::cout << "Size of type: " << sizeof(T)
<< " Quantity: " << len
<< " Total Size: " << sizeof arr << '\n';
}

template<class T>
void Display(T const &obj)
{
Display(reinterpret_cast<T const (&)[1]>(obj));
}

int main()
{
int obj;

int arr[5];

Display(obj);
Display(arr);
}