...during the call to swap_arrays the name of the array decays to a
pointer to its first element and that pointer is a temporary variable
and you cant bind a non-const reference to a temporary. Correct
analysis?
The code (that only compiles if you comment out the call to
swap_arrays()):
#include <iostream>
#include <iterator>
using namespace std;
void swap_arrays(int *&a1, int *&a2)
{
int *ptr = a1;
a1 = a2;
a2 = ptr;
}
int main()
{
int array1[] = {1, 2, 3};
int array2[] = {4, 5, 6};
swap_arrays(arr ay1[0], array2[0]);
cout << "array1 after swap:" << endl;
copy(array1, array1 + sizeof(array1) / sizeof(array1[0]),
ostream_iterato r<int>(cout, " "));
cout << endl << "array2 after swap:" << endl;
copy(array2, array2 + sizeof(array2) / sizeof(array2[0]),
ostream_iterato r<int>(cout, " "));
cout << endl;
} 2 3567
Eric Lilja wrote:
..during the call to swap_arrays the name of the array decays to a
pointer to its first element and that pointer is a temporary variable
and you cant bind a non-const reference to a temporary. Correct
analysis?
I don't think so.
The code (that only compiles if you comment out the call to
swap_arrays()):
#include <iostream>
#include <iterator>
using namespace std;
void swap_arrays(int *&a1, int *&a2)
{
int *ptr = a1;
a1 = a2;
a2 = ptr;
}
That function will not swap arrays. It swaps objects of type pointer-to-int.
>
int main()
{
int array1[] = {1, 2, 3};
int array2[] = {4, 5, 6};
swap_arrays(arr ay1[0], array2[0]);
You promised int*& as the parameter. What you pass is int&.
cout << "array1 after swap:" << endl;
copy(array1, array1 + sizeof(array1) / sizeof(array1[0]),
ostream_iterato r<int>(cout, " "));
cout << endl << "array2 after swap:" << endl;
copy(array2, array2 + sizeof(array2) / sizeof(array2[0]),
ostream_iterato r<int>(cout, " "));
cout << endl;
}
Try this:
#include <cstddef>
#include <algorithm>
using namespace std;
template < typename T, std::size_t N >
void swap ( T (&lhs) [N], T (&rhs) [N] ) {
for ( std::size_t i = 0; i < N; ++i ) {
swap( lhs[i], rhs[i] );
}
}
#include <iostream>
#include <iterator>
using namespace std;
int main ( void ) {
int array1[] = {1, 2, 3};
int array2[] = {4, 5, 6};
swap( array1, array2 );
cout << "array1 after swap:" << endl;
copy(array1, array1 + sizeof(array1) / sizeof(array1[0]),
ostream_iterato r<int>(cout, " "));
cout << endl << "array2 after swap:" << endl;
copy(array2, array2 + sizeof(array2) / sizeof(array2[0]),
ostream_iterato r<int>(cout, " "));
cout << endl;
}
Best
Kai-Uwe Bux
Eric Lilja wrote:
...during the call to swap_arrays the name of the array decays to a
pointer to its first element and that pointer is a temporary variable
and you cant bind a non-const reference to a temporary. Correct
analysis?
Yes and no.
....
void swap_arrays(int *&a1, int *&a2)
....
int array1[] = {1, 2, 3};
int array2[] = {4, 5, 6};
swap_arrays(arr ay1[0], array2[0]);
As it is, you are passing two (int) objects where to (int*) objects are
expected. Though, even if you change this to what I *assume* you
actually meant:
swap_arrays(arr ay1, array2);
then your above analysis is correct, and the code still won't work. You
would have the same problem with:
void swap_double(dou ble &d1, double &d2)
{
double temp = d1;
d1 = d2;
d2 = temp;
}
....
float f1 = 1, f2 = 2;
swap_double(f1, f2);
--
Clark S. Cox III cl*******@gmail .com This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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