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17.2 Slicing with Range Indexes

Slicing returns a contiguous slice of a one-dimensional array, a contiguous sub-block of a two-dimensional array, and so on. Semantically, it is just a special form of multiple indexing.

Lower and Upper Bound Indexes

For instance, consider supplying an upper and lower bound for an index.

int c[7];
...
int d[4];
d = c[3:6];  // result: d == (c[3], c[4], c[5], c[6])

The range index 3:6 behaves semantically just like the multiple index (3, 4, 5, 6). In terms of implementation, the sliced upper and/or lower bounded indices are faster and use less memory because they do not explicitly create a multiple index, but rather use a direct loop. They are also easier to read, so should be preferred over multiple indexes where applicable.

Lower or Upper Bound Indexes

It is also possible to supply just a lower bound, or just an upper bound. Writing c[3:] is just shorthand for c[3:size(c)]. Writing c[:5] is just shorthand for c[1:5].

Full Range Indexes

Finally, it is possible to write a range index that covers the entire range of an array, either by including just the range symbol (:) as the index or leaving the index position empty. In both cases, c[] and c[:] are equal to c[1:size(c)], which in turn is just equal to c.