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<h3 class="section">17.1 Assignment to Variables</h3>

<p><a name="index-assignment-1164"></a><a name="index-setting-variables-1165"></a>To alter the value of a variable, evaluate an assignment expression. 
See <a href="Expressions.html#Expressions">Expressions</a>.  For example,

<pre class="smallexample">     print x=4
</pre>
   <p class="noindent">stores the value 4 into the variable <code>x</code>, and then prints the
value of the assignment expression (which is 4). 
See <a href="Languages.html#Languages">Using <span class="sc">gdb</span> with Different Languages</a>, for more
information on operators in supported languages.

   <p><a name="index-set-variable-1166"></a><a name="index-variables_002c-setting-1167"></a>If you are not interested in seeing the value of the assignment, use the
<code>set</code> command instead of the <code>print</code> command.  <code>set</code> is
really the same as <code>print</code> except that the expression's value is
not printed and is not put in the value history (see <a href="Value-History.html#Value-History">Value History</a>).  The expression is evaluated only for its effects.

   <p>If the beginning of the argument string of the <code>set</code> command
appears identical to a <code>set</code> subcommand, use the <code>set
variable</code> command instead of just <code>set</code>.  This command is identical
to <code>set</code> except for its lack of subcommands.  For example, if your
program has a variable <code>width</code>, you get an error if you try to set
a new value with just &lsquo;<samp><span class="samp">set width=13</span></samp>&rsquo;, because <span class="sc">gdb</span> has the
command <code>set width</code>:

<pre class="smallexample">     (gdb) whatis width
     type = double
     (gdb) p width
     $4 = 13
     (gdb) set width=47
     Invalid syntax in expression.
</pre>
   <p class="noindent">The invalid expression, of course, is &lsquo;<samp><span class="samp">=47</span></samp>&rsquo;.  In
order to actually set the program's variable <code>width</code>, use

<pre class="smallexample">     (gdb) set var width=47
</pre>
   <p>Because the <code>set</code> command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the
<code>set variable</code> command instead of just <code>set</code>.  For example, if
your program has a variable <code>g</code>, you run into problems if you try
to set a new value with just &lsquo;<samp><span class="samp">set g=4</span></samp>&rsquo;, because <span class="sc">gdb</span> has
the command <code>set gnutarget</code>, abbreviated <code>set g</code>:

<pre class="smallexample">     (gdb) whatis g
     type = double
     (gdb) p g
     $1 = 1
     (gdb) set g=4
     (gdb) p g
     $2 = 1
     (gdb) r
     The program being debugged has been started already.
     Start it from the beginning? (y or n) y
     Starting program: /home/smith/cc_progs/a.out
     "/home/smith/cc_progs/a.out": can't open to read symbols:
                                      Invalid bfd target.
     (gdb) show g
     The current BFD target is "=4".
</pre>
   <p class="noindent">The program variable <code>g</code> did not change, and you silently set the
<code>gnutarget</code> to an invalid value.  In order to set the variable
<code>g</code>, use

<pre class="smallexample">     (gdb) set var g=4
</pre>
   <p><span class="sc">gdb</span> allows more implicit conversions in assignments than C; you can
freely store an integer value into a pointer variable or vice versa,
and you can convert any structure to any other structure that is the
same length or shorter. 
<!-- FIXME: how do structs align/pad in these conversions? -->
<!-- /doc@cygnus.com 18dec1990 -->

   <p>To store values into arbitrary places in memory, use the &lsquo;<samp><span class="samp">{...}</span></samp>&rsquo;
construct to generate a value of specified type at a specified address
(see <a href="Expressions.html#Expressions">Expressions</a>).  For example, <code>{int}0x83040</code> refers
to memory location <code>0x83040</code> as an integer (which implies a certain size
and representation in memory), and

<pre class="smallexample">     set {int}0x83040 = 4
</pre>
   <p class="noindent">stores the value 4 into that memory location.

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