Let's say I have following templated C class
#include <cstdint>
template <uint32_t NO_POINTS>
class A
{
public:
struct Point
{
float x;
float y;
};
A(const Point (&points)[NO_POINTS])
{
for (uint32_t point = 0; point < NO_POINTS; point ) {
table[point] = points[point];
}
}
private:
Point table[NO_POINTS];
};
and I would like to use an instance of this class as a private member of the following class:
#include "A.h"
template <uint32_t NO_LUT_POINTS>
class B
{
public:
B(A<NO_LUT_POINTS>::Point (&table)[NO_LUT_POINTS]) : lut(table){}
private:
A<NO_LUT_POINTS> lut;
};
#include "B.h"
int main(int argc, char** argv) {
B<4> foo({{1326.0, 25.0}, {1601.0, 30.0}, {1922.0, 35.0}, {2293.0, 40.0}});
return 0;
}
I have attempted to compile this code but the compiler reports following error
A<NO_LUT_POINTS>::Point is not a type
. I don't understand what the reason for this error is. Can anybody explain to me why the compiler reports this error?
CodePudding user response:
This is a common mistake with types nested in template classes. You need to add typename
to tell the compiler that Point
is a type.
...
public:
B(typename A<NO_LUT_POINTS>::Point const (&table)[NO_LUT_POINTS]) : lut(table){}
...
Beyond solving your problem, however, please notice that Point
doesn't depend on the template parameters of A
, so you should not nest it in that class. This would remove the necessity for adding typename
.