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Some problems with the template

template<class TypeIterator>
void Generate(const TypeIterator& first, const TypeIterator& last)
{
    //do something
}

When I tried to call the generate function like this:

PhanSo arr[10];
Generate(arr, arr+10);

I got the error: void Generate (const TypeIterator &, const TypeIterator &) ': template parameter' TypeIterator 'is ambiguous

When I used:

PhanSo arr[10];
Generate(&arr[0], &arr[10]);

Then my program was executed successfully.

I tried to fix this by removing the "&" in the function parameter

template<class TypeIterator>
void Generate(const TypeIterator first, const TypeIterator last);

Then there is no mistake. Can anyone explain this to me?

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2 answers


The array is not a pointer. The array name used as a pointer to the first element of the array is just syntactic sugar .

If the template parameter is a reference , there will be no conversion between arrays and pointers.

When you called void Generate(const TypeIterator& first, const TypeIterator& last)

with Generate(arr, arr+10);

, it arr

resolves to PhanSo[10]

, and arr+10

goes to PhanSo*

, which has actually been pointed out by both the g ++ compilers and Microsoft as an ambiguity.



When you called void Generate(const TypeIterator& first, const TypeIterator& last)

with Generate(&arr[0], &arr[10]);

, things became much clearer to the compiler because you are specifically supplying the element with the address of the elements, so the TypeIterator allows PhanSo*

.

Finally, when you called void Generate(const TypeIterator first, const TypeIterator last)

with Generate(arr, arr+10);

, since the template parameter is no longer a reference , the normal array to pointer conversion takes place and TypeIterator

resolved PhanSo*

.

Thanks for reading.

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When you call Generate(arr, arr+10);

  • first

    will be const PhanSo (&)[10]

    .
  • but second

    decomposes into a pointer: const PhanSo *

    .

and hence the type mismatch.



Since an array cannot be passed by arr

fading value too much for a pointer if you have

template<class TypeIterator>
void Generate(const TypeIterator first, const TypeIterator last);

without reference.

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