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| <h3 class="section">8.9 Protections</h3> |
| |
| <p>In the simple class definition shown above all member data and |
| functions were publicly accessible. The example that follows |
| contrasts public, protected and privately accessible fields and shows |
| how these protections are encoded in C<tt>++</tt> stabs. |
| |
| <p>If the character following the ‘<samp><var>field-name</var><span class="samp">:</span></samp>’ part of the |
| string is ‘<samp><span class="samp">/</span></samp>’, then the next character is the visibility. ‘<samp><span class="samp">0</span></samp>’ |
| means private, ‘<samp><span class="samp">1</span></samp>’ means protected, and ‘<samp><span class="samp">2</span></samp>’ means public. |
| Debuggers should ignore visibility characters they do not recognize, and |
| assume a reasonable default (such as public) (GDB 4.11 does not, but |
| this should be fixed in the next GDB release). If no visibility is |
| specified the field is public. The visibility ‘<samp><span class="samp">9</span></samp>’ means that the |
| field has been optimized out and is public (there is no way to specify |
| an optimized out field with a private or protected visibility). |
| Visibility ‘<samp><span class="samp">9</span></samp>’ is not supported by GDB 4.11; this should be fixed |
| in the next GDB release. |
| |
| <p>The following C<tt>++</tt> source: |
| |
| <pre class="example"> class vis { |
| private: |
| int priv; |
| protected: |
| char prot; |
| public: |
| float pub; |
| }; |
| </pre> |
| <p class="noindent">generates the following stab: |
| |
| <pre class="example"> # <span class="roman">128 is N_LSYM</span> |
| .stabs "vis:T19=s12priv:/01,0,32;prot:/12,32,8;pub:12,64,32;;",128,0,0,0 |
| </pre> |
| <p>‘<samp><span class="samp">vis:T19=s12</span></samp>’ indicates that type number 19 is a 12 byte structure |
| named <code>vis</code> The <code>priv</code> field has public visibility |
| (‘<samp><span class="samp">/0</span></samp>’), type int (‘<samp><span class="samp">1</span></samp>’), and offset and size ‘<samp><span class="samp">,0,32;</span></samp>’. |
| The <code>prot</code> field has protected visibility (‘<samp><span class="samp">/1</span></samp>’), type char |
| (‘<samp><span class="samp">2</span></samp>’) and offset and size ‘<samp><span class="samp">,32,8;</span></samp>’. The <code>pub</code> field has |
| type float (‘<samp><span class="samp">12</span></samp>’), and offset and size ‘<samp><span class="samp">,64,32;</span></samp>’. |
| |
| <p>Protections for member functions are signified by one digit embedded in |
| the field part of the stab describing the method. The digit is 0 if |
| private, 1 if protected and 2 if public. Consider the C<tt>++</tt> class |
| definition below: |
| |
| <pre class="example"> class all_methods { |
| private: |
| int priv_meth(int in){return in;}; |
| protected: |
| char protMeth(char in){return in;}; |
| public: |
| float pubMeth(float in){return in;}; |
| }; |
| </pre> |
| <p>It generates the following stab. The digit in question is to the left |
| of an ‘<samp><span class="samp">A</span></samp>’ in each case. Notice also that in this case two symbol |
| descriptors apply to the class name struct tag and struct type. |
| |
| <pre class="display"> .stabs "class_name:sym_desc(struct tag&type)type_def(21)= |
| sym_desc(struct)struct_bytes(1) |
| meth_name::type_def(22)=sym_desc(method)returning(int); |
| :args(int);protection(private)modifier(normal)virtual(no); |
| meth_name::type_def(23)=sym_desc(method)returning(char); |
| :args(char);protection(protected)modifier(normal)virtual(no); |
| meth_name::type_def(24)=sym_desc(method)returning(float); |
| :args(float);protection(public)modifier(normal)virtual(no);;", |
| N_LSYM,NIL,NIL,NIL |
| </pre> |
| <pre class="smallexample"> .stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.; |
| pubMeth::24=##12;:f;2A.;;",128,0,0,0 |
| </pre> |
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