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| Next: <a href="Typedefs.html#Typedefs" accesskey="n" rel="next">Typedefs</a>, Previous: <a href="Enumerations.html#Enumerations" accesskey="p" rel="prev">Enumerations</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Structures-1"></a> |
| <h3 class="section">5.8 Structures</h3> |
| |
| <p>The encoding of structures in stabs can be shown with an example. |
| </p> |
| <p>The following source code declares a structure tag and defines an |
| instance of the structure in global scope. Then a <code>typedef</code> equates the |
| structure tag with a new type. Separate stabs are generated for the |
| structure tag, the structure <code>typedef</code>, and the structure instance. The |
| stabs for the tag and the <code>typedef</code> are emitted when the definitions are |
| encountered. Since the structure elements are not initialized, the |
| stab and code for the structure variable itself is located at the end |
| of the program in the bss section. |
| </p> |
| <div class="example"> |
| <pre class="example">struct s_tag { |
| int s_int; |
| float s_float; |
| char s_char_vec[8]; |
| struct s_tag* s_next; |
| } g_an_s; |
| |
| typedef struct s_tag s_typedef; |
| </pre></div> |
| |
| <p>The structure tag has an <code>N_LSYM</code> stab type because, like the |
| enumeration, the symbol has file scope. Like the enumeration, the |
| symbol descriptor is ‘<samp>T</samp>’, for enumeration, structure, or tag type. |
| The type descriptor ‘<samp>s</samp>’ following the ‘<samp>16=</samp>’ of the type |
| definition narrows the symbol type to structure. |
| </p> |
| <p>Following the ‘<samp>s</samp>’ type descriptor is the number of bytes the |
| structure occupies, followed by a description of each structure element. |
| The structure element descriptions are of the form |
| ‘<samp><var>name</var>:<var>type</var>, <var>bit offset from the start of the |
| struct</var>, <var>number of bits in the element</var></samp>’. |
| </p> |
| <div class="example"> |
| <pre class="example"># <span class="roman">128 is N_LSYM</span> |
| .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32; |
| s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0 |
| </pre></div> |
| |
| <p>In this example, the first two structure elements are previously defined |
| types. For these, the type following the ‘<samp><var>name</var>:</samp>’ part of the |
| element description is a simple type reference. The other two structure |
| elements are new types. In this case there is a type definition |
| embedded after the ‘<samp><var>name</var>:</samp>’. The type definition for the |
| array element looks just like a type definition for a stand-alone array. |
| The <code>s_next</code> field is a pointer to the same kind of structure that |
| the field is an element of. So the definition of structure type 16 |
| contains a type definition for an element which is a pointer to type 16. |
| </p> |
| <p>If a field is a static member (this is a C<tt>++</tt> feature in which a single |
| variable appears to be a field of every structure of a given type) it |
| still starts out with the field name, a colon, and the type, but then |
| instead of a comma, bit position, comma, and bit size, there is a colon |
| followed by the name of the variable which each such field refers to. |
| </p> |
| <p>If the structure has methods (a C<tt>++</tt> feature), they follow the non-method |
| fields; see <a href="Cplusplus.html#Cplusplus">Cplusplus</a>. |
| </p> |
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