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| <h3 class="section">10.10 Value History</h3> |
| |
| <p><a name="index-value-history-717"></a><a name="index-history-of-values-printed-by-_0040value_007bGDBN_007d-718"></a>Values printed by the <code>print</code> command are saved in the <span class="sc">gdb</span> |
| <dfn>value history</dfn>. This allows you to refer to them in other expressions. |
| Values are kept until the symbol table is re-read or discarded |
| (for example with the <code>file</code> or <code>symbol-file</code> commands). |
| When the symbol table changes, the value history is discarded, |
| since the values may contain pointers back to the types defined in the |
| symbol table. |
| |
| <p><a name="index-g_t_0040code_007b_0024_007d-719"></a><a name="index-g_t_0040code_007b_0024_0024_007d-720"></a><a name="index-history-number-721"></a>The values printed are given <dfn>history numbers</dfn> by which you can |
| refer to them. These are successive integers starting with one. |
| <code>print</code> shows you the history number assigned to a value by |
| printing ‘<samp><span class="samp">$</span><var>num</var><span class="samp"> = </span></samp>’ before the value; here <var>num</var> is the |
| history number. |
| |
| <p>To refer to any previous value, use ‘<samp><span class="samp">$</span></samp>’ followed by the value's |
| history number. The way <code>print</code> labels its output is designed to |
| remind you of this. Just <code>$</code> refers to the most recent value in |
| the history, and <code>$$</code> refers to the value before that. |
| <code>$$</code><var>n</var> refers to the <var>n</var>th value from the end; <code>$$2</code> |
| is the value just prior to <code>$$</code>, <code>$$1</code> is equivalent to |
| <code>$$</code>, and <code>$$0</code> is equivalent to <code>$</code>. |
| |
| <p>For example, suppose you have just printed a pointer to a structure and |
| want to see the contents of the structure. It suffices to type |
| |
| <pre class="smallexample"> p *$ |
| </pre> |
| <p>If you have a chain of structures where the component <code>next</code> points |
| to the next one, you can print the contents of the next one with this: |
| |
| <pre class="smallexample"> p *$.next |
| </pre> |
| <p class="noindent">You can print successive links in the chain by repeating this |
| command—which you can do by just typing <RET>. |
| |
| <p>Note that the history records values, not expressions. If the value of |
| <code>x</code> is 4 and you type these commands: |
| |
| <pre class="smallexample"> print x |
| set x=5 |
| </pre> |
| <p class="noindent">then the value recorded in the value history by the <code>print</code> command |
| remains 4 even though the value of <code>x</code> has changed. |
| |
| |
| <a name="index-show-values-722"></a> |
| <dl><dt><code>show values</code><dd>Print the last ten values in the value history, with their item numbers. |
| This is like ‘<samp><span class="samp">p $$9</span></samp>’ repeated ten times, except that <code>show |
| values</code> does not change the history. |
| |
| <br><dt><code>show values </code><var>n</var><dd>Print ten history values centered on history item number <var>n</var>. |
| |
| <br><dt><code>show values +</code><dd>Print ten history values just after the values last printed. If no more |
| values are available, <code>show values +</code> produces no display. |
| </dl> |
| |
| <p>Pressing <RET> to repeat <code>show values </code><var>n</var> has exactly the |
| same effect as ‘<samp><span class="samp">show values +</span></samp>’. |
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