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| <h3 class="section">5.5 Array Types</h3> |
| |
| <p>Arrays use the ‘<samp><span class="samp">a</span></samp>’ type descriptor. Following the type descriptor |
| is the type of the index and the type of the array elements. If the |
| index type is a range type, it ends in a semicolon; otherwise |
| (for example, if it is a type reference), there does not |
| appear to be any way to tell where the types are separated. In an |
| effort to clean up this mess, IBM documents the two types as being |
| separated by a semicolon, and a range type as not ending in a semicolon |
| (but this is not right for range types which are not array indexes, |
| see <a href="Subranges.html#Subranges">Subranges</a>). I think probably the best solution is to specify |
| that a semicolon ends a range type, and that the index type and element |
| type of an array are separated by a semicolon, but that if the index |
| type is a range type, the extra semicolon can be omitted. GDB (at least |
| through version 4.9) doesn't support any kind of index type other than a |
| range anyway; I'm not sure about dbx. |
| |
| <p>It is well established, and widely used, that the type of the index, |
| unlike most types found in the stabs, is merely a type definition, not |
| type information (see <a href="String-Field.html#String-Field">String Field</a>) (that is, it need not start with |
| ‘<samp><var>type-number</var><span class="samp">=</span></samp>’ if it is defining a new type). According to a |
| comment in GDB, this is also true of the type of the array elements; it |
| gives ‘<samp><span class="samp">ar1;1;10;ar1;1;10;4</span></samp>’ as a legitimate way to express a two |
| dimensional array. According to AIX documentation, the element type |
| must be type information. GDB accepts either. |
| |
| <p>The type of the index is often a range type, expressed as the type |
| descriptor ‘<samp><span class="samp">r</span></samp>’ and some parameters. It defines the size of the |
| array. In the example below, the range ‘<samp><span class="samp">r1;0;2;</span></samp>’ defines an index |
| type which is a subrange of type 1 (integer), with a lower bound of 0 |
| and an upper bound of 2. This defines the valid range of subscripts of |
| a three-element C array. |
| |
| <p>For example, the definition: |
| |
| <pre class="example"> char char_vec[3] = {'a','b','c'}; |
| </pre> |
| <p class="noindent">produces the output: |
| |
| <pre class="example"> .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0 |
| .global _char_vec |
| .align 4 |
| _char_vec: |
| .byte 97 |
| .byte 98 |
| .byte 99 |
| </pre> |
| <p>If an array is <dfn>packed</dfn>, the elements are spaced more |
| closely than normal, saving memory at the expense of speed. For |
| example, an array of 3-byte objects might, if unpacked, have each |
| element aligned on a 4-byte boundary, but if packed, have no padding. |
| One way to specify that something is packed is with type attributes |
| (see <a href="String-Field.html#String-Field">String Field</a>). In the case of arrays, another is to use the |
| ‘<samp><span class="samp">P</span></samp>’ type descriptor instead of ‘<samp><span class="samp">a</span></samp>’. Other than specifying a |
| packed array, ‘<samp><span class="samp">P</span></samp>’ is identical to ‘<samp><span class="samp">a</span></samp>’. |
| |
| <!-- FIXME-what is it? A pointer? --> |
| <p>An open array is represented by the ‘<samp><span class="samp">A</span></samp>’ type descriptor followed by |
| type information specifying the type of the array elements. |
| |
| <!-- FIXME: what is the format of this type? A pointer to a vector of pointers? --> |
| <p>An N-dimensional dynamic array is represented by |
| |
| <pre class="example"> D <var>dimensions</var> ; <var>type-information</var> |
| </pre> |
| <!-- Does dimensions really have this meaning? The AIX documentation --> |
| <!-- doesn't say. --> |
| <p><var>dimensions</var> is the number of dimensions; <var>type-information</var> |
| specifies the type of the array elements. |
| |
| <!-- FIXME: what is the format of this type? A pointer to some offsets in --> |
| <!-- another array? --> |
| <p>A subarray of an N-dimensional array is represented by |
| |
| <pre class="example"> E <var>dimensions</var> ; <var>type-information</var> |
| </pre> |
| <!-- Does dimensions really have this meaning? The AIX documentation --> |
| <!-- doesn't say. --> |
| <p><var>dimensions</var> is the number of dimensions; <var>type-information</var> |
| specifies the type of the array elements. |
| |
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