Repeating index - Indirect arrays - valarray

[suresh]

Namasivayah,

Stroustrup says when indirect array is used for reordering a valarray
the index cannot be repeated twice(page 679). But Nicolai Josuttis in
his book on C++ standard library, page 567, says, index may occur
twice.

g++ version 3.3.5 compiles code with repeated index without any
complaint.

My questions are

1. Can we repeat the index in the index array for reordering a
valarray?
2. Can I get a reordered array which is larger than the original array
by repeating indices. (It works in g++, but I am not sure of
portability)

Thank you,
suresh


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[Carl Barron]

Namasivayah,

Stroustrup says when indirect array is used for reordering a valarray
the index cannot be repeated twice(page 679). But Nicolai Josuttis in
his book on C++ standard library, page 567, says, index may occur
twice.

g++ version 3.3.5 compiles code with repeated index without any
complaint.

My questions are

1. Can we repeat the index in the index array for reordering a
valarray?
2. Can I get a reordered array which is larger than the original array
by repeating indices. (It works in g++, but I am not sure of
portability)

section 26.3.9.2 states its undefined behavior in the example in par
3:
[ Example:
int addr [] = {2 , 3 , 1 , 4 , 4};
valarray <size_t > indirect (addr , 5);
valarray <double > a (0. , 10) , b (1. , 5);
a[ indirect ] = b;
results in undefined behavior since element 4 is specified twice in the
indirection. ‹end example ]

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