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<TITLE>Debugging with GDB: Sequences</TITLE>
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<A NAME="SEC229"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_20.html#SEC228"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC230"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H1> 20. Canned Sequences of Commands </H1>
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<!--docid::SEC229::-->
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<P>
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Aside from breakpoint commands (see section <A HREF="gdb_6.html#SEC39">Breakpoint Command Lists</A>), GDB provides two ways to store sequences of
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commands for execution as a unit: user-defined commands and command
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files.
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</P><P>
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<BLOCKQUOTE><TABLE BORDER=0 CELLSPACING=0>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_21.html#SEC230">20.1 User-defined Commands</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">How to define your own commands</TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_21.html#SEC231">20.2 User-defined Command Hooks</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Hooks for user-defined commands</TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_21.html#SEC232">20.3 Command Files</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">How to write scripts of commands to be stored in a file</TD></TR>
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<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="gdb_21.html#SEC233">20.4 Commands for Controlled Output</A></TD><TD> </TD><TD ALIGN="left" VALIGN="TOP">Commands for controlled output</TD></TR>
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</TABLE></BLOCKQUOTE>
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<P>
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<A NAME="Define"></A>
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<HR SIZE="6">
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<A NAME="SEC230"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 20.1 User-defined Commands </H2>
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<!--docid::SEC230::-->
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<P>
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<A NAME="IDX1183"></A>
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<A NAME="IDX1184"></A>
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A <EM>user-defined command</EM> is a sequence of GDB commands to
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which you assign a new name as a command. This is done with the
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<CODE>define</CODE> command. User commands may accept up to 10 arguments
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separated by whitespace. Arguments are accessed within the user command
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via <CODE>$arg0<small>...</small>$arg9</CODE>. A trivial example:
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>define adder
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print $arg0 + $arg1 + $arg2
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end
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</FONT></pre></td></tr></table></P><P>
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To execute the command use:
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>adder 1 2 3
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</FONT></pre></td></tr></table></P><P>
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This defines the command <CODE>adder</CODE>, which prints the sum of
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its three arguments. Note the arguments are text substitutions, so they may
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reference variables, use complex expressions, or even perform inferior
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functions calls.
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</P><P>
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<A NAME="IDX1185"></A>
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<A NAME="IDX1186"></A>
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In addition, <CODE>$argc</CODE> may be used to find out how many arguments have
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been passed. This expands to a number in the range 0<small>...</small>10.
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>define adder
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if $argc == 2
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print $arg0 + $arg1
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end
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if $argc == 3
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print $arg0 + $arg1 + $arg2
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end
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end
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</FONT></pre></td></tr></table></P><P>
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<DL COMPACT>
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<A NAME="IDX1187"></A>
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<DT><CODE>define <VAR>commandname</VAR></CODE>
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<DD>Define a command named <VAR>commandname</VAR>. If there is already a command
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by that name, you are asked to confirm that you want to redefine it.
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<P>
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The definition of the command is made up of other GDB command lines,
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which are given following the <CODE>define</CODE> command. The end of these
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commands is marked by a line containing <CODE>end</CODE>.
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</P><P>
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<A NAME="IDX1188"></A>
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<A NAME="IDX1189"></A>
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<DT><CODE>document <VAR>commandname</VAR></CODE>
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<DD>Document the user-defined command <VAR>commandname</VAR>, so that it can be
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accessed by <CODE>help</CODE>. The command <VAR>commandname</VAR> must already be
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defined. This command reads lines of documentation just as <CODE>define</CODE>
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reads the lines of the command definition, ending with <CODE>end</CODE>.
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After the <CODE>document</CODE> command is finished, <CODE>help</CODE> on command
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<VAR>commandname</VAR> displays the documentation you have written.
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<P>
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You may use the <CODE>document</CODE> command again to change the
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documentation of a command. Redefining the command with <CODE>define</CODE>
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does not change the documentation.
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</P><P>
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<A NAME="IDX1190"></A>
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<A NAME="IDX1191"></A>
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<DT><CODE>dont-repeat</CODE>
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<DD>Used inside a user-defined command, this tells GDB that this
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command should not be repeated when the user hits <KBD>RET</KBD>
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(see section <A HREF="gdb_4.html#SEC15">repeat last command</A>).
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<P>
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<A NAME="IDX1192"></A>
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<DT><CODE>help user-defined</CODE>
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<DD>List all user-defined commands, with the first line of the documentation
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(if any) for each.
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<P>
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<A NAME="IDX1193"></A>
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<DT><CODE>show user</CODE>
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<DD><DT><CODE>show user <VAR>commandname</VAR></CODE>
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<DD>Display the GDB commands used to define <VAR>commandname</VAR> (but
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not its documentation). If no <VAR>commandname</VAR> is given, display the
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definitions for all user-defined commands.
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<P>
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<A NAME="IDX1194"></A>
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<A NAME="IDX1195"></A>
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<A NAME="IDX1196"></A>
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<DT><CODE>show max-user-call-depth</CODE>
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<DD><DT><CODE>set max-user-call-depth</CODE>
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<DD>The value of <CODE>max-user-call-depth</CODE> controls how many recursion
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levels are allowed in user-defined commands before GDB suspects an
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infinite recursion and aborts the command.
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</DL>
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<P>
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In addition to the above commands, user-defined commands frequently
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use control flow commands, described in <A HREF="gdb_21.html#SEC232">20.3 Command Files</A>.
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</P><P>
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When user-defined commands are executed, the
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commands of the definition are not printed. An error in any command
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stops execution of the user-defined command.
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</P><P>
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If used interactively, commands that would ask for confirmation proceed
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without asking when used inside a user-defined command. Many GDB
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commands that normally print messages to say what they are doing omit the
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messages when used in a user-defined command.
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</P><P>
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<A NAME="Hooks"></A>
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<HR SIZE="6">
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<A NAME="SEC231"></A>
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC230"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC232"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC232"> << </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> Up </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
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</TR></TABLE>
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<H2> 20.2 User-defined Command Hooks </H2>
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<!--docid::SEC231::-->
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<P>
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<A NAME="IDX1197"></A>
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You may define <EM>hooks</EM>, which are a special kind of user-defined
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command. Whenever you run the command <SAMP>`foo'</SAMP>, if the user-defined
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command <SAMP>`hook-foo'</SAMP> exists, it is executed (with no arguments)
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before that command.
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</P><P>
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<A NAME="IDX1198"></A>
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<A NAME="IDX1199"></A>
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A hook may also be defined which is run after the command you executed.
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Whenever you run the command <SAMP>`foo'</SAMP>, if the user-defined command
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<SAMP>`hookpost-foo'</SAMP> exists, it is executed (with no arguments) after
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that command. Post-execution hooks may exist simultaneously with
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pre-execution hooks, for the same command.
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</P><P>
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It is valid for a hook to call the command which it hooks. If this
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occurs, the hook is not re-executed, thereby avoiding infinite recursion.
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</P><P>
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<A NAME="IDX1200"></A>
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In addition, a pseudo-command, <SAMP>`stop'</SAMP> exists. Defining
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(<SAMP>`hook-stop'</SAMP>) makes the associated commands execute every time
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execution stops in your program: before breakpoint commands are run,
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displays are printed, or the stack frame is printed.
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</P><P>
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For example, to ignore <CODE>SIGALRM</CODE> signals while
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single-stepping, but treat them normally during normal execution,
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you could define:
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>define hook-stop
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handle SIGALRM nopass
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end
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define hook-run
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handle SIGALRM pass
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end
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define hook-continue
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handle SIGALRM pass
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end
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</FONT></pre></td></tr></table></P><P>
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As a further example, to hook at the beginning and end of the <CODE>echo</CODE>
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command, and to add extra text to the beginning and end of the message,
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you could define:
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</P><P>
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>define hook-echo
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echo <<<---
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end
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define hookpost-echo
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echo --->>>\n
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end
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(gdb) echo Hello World
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<<<---Hello World--->>>
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(gdb)
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</FONT></pre></td></tr></table></P><P>
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You can define a hook for any single-word command in GDB, but
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not for command aliases; you should define a hook for the basic command
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name, e.g. <CODE>backtrace</CODE> rather than <CODE>bt</CODE>.
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If an error occurs during the execution of your hook, execution of
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GDB commands stops and GDB issues a prompt
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(before the command that you actually typed had a chance to run).
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</P><P>
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If you try to define a hook which does not match any known command, you
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get a warning from the <CODE>define</CODE> command.
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</P><P>
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<A NAME="Command Files"></A>
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<HR SIZE="6">
|
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<A NAME="SEC232"></A>
|
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<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
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<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC231"> < </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC233"> > </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC233"> << </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> Up </A>]</TD>
|
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> >> </A>]</TD>
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<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
|
</TR></TABLE>
|
|
<H2> 20.3 Command Files </H2>
|
|
<!--docid::SEC232::-->
|
|
<P>
|
|
|
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<A NAME="IDX1201"></A>
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|
<A NAME="IDX1202"></A>
|
|
A command file for GDB is a text file made of lines that are
|
|
GDB commands. Comments (lines starting with <KBD>#</KBD>) may
|
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also be included. An empty line in a command file does nothing; it
|
|
does not mean to repeat the last command, as it would from the
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terminal.
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</P><P>
|
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You can request the execution of a command file with the <CODE>source</CODE>
|
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command:
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</P><P>
|
|
|
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<DL COMPACT>
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|
<A NAME="IDX1203"></A>
|
|
<A NAME="IDX1204"></A>
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<DT><CODE>source [<CODE>-v</CODE>] <VAR>filename</VAR></CODE>
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<DD>Execute the command file <VAR>filename</VAR>.
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</DL>
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<P>
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|
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The lines in a command file are generally executed sequentially,
|
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unless the order of execution is changed by one of the
|
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<EM>flow-control commands</EM> described below. The commands are not
|
|
printed as they are executed. An error in any command terminates
|
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execution of the command file and control is returned to the console.
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</P><P>
|
|
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GDB searches for <VAR>filename</VAR> in the current directory and then
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on the search path (specified with the <SAMP>`directory'</SAMP> command).
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</P><P>
|
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If <CODE>-v</CODE>, for verbose mode, is given then GDB displays
|
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each command as it is executed. The option must be given before
|
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<VAR>filename</VAR>, and is interpreted as part of the filename anywhere else.
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</P><P>
|
|
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Commands that would ask for confirmation if used interactively proceed
|
|
without asking when used in a command file. Many GDB commands that
|
|
normally print messages to say what they are doing omit the messages
|
|
when called from command files.
|
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</P><P>
|
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GDB also accepts command input from standard input. In this
|
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mode, normal output goes to standard output and error output goes to
|
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standard error. Errors in a command file supplied on standard input do
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not terminate execution of the command file--execution continues with
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the next command.
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</P><P>
|
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<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>gdb < cmds > log 2>&1
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</FONT></pre></td></tr></table></P><P>
|
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(The syntax above will vary depending on the shell used.) This example
|
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will execute commands from the file <TT>`cmds'</TT>. All output and errors
|
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would be directed to <TT>`log'</TT>.
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</P><P>
|
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Since commands stored on command files tend to be more general than
|
|
commands typed interactively, they frequently need to deal with
|
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complicated situations, such as different or unexpected values of
|
|
variables and symbols, changes in how the program being debugged is
|
|
built, etc. GDB provides a set of flow-control commands to
|
|
deal with these complexities. Using these commands, you can write
|
|
complex scripts that loop over data structures, execute commands
|
|
conditionally, etc.
|
|
</P><P>
|
|
|
|
<DL COMPACT>
|
|
<A NAME="IDX1205"></A>
|
|
<A NAME="IDX1206"></A>
|
|
<DT><CODE>if</CODE>
|
|
<DD><DT><CODE>else</CODE>
|
|
<DD>This command allows to include in your script conditionally executed
|
|
commands. The <CODE>if</CODE> command takes a single argument, which is an
|
|
expression to evaluate. It is followed by a series of commands that
|
|
are executed only if the expression is true (its value is nonzero).
|
|
There can then optionally be an <CODE>else</CODE> line, followed by a series
|
|
of commands that are only executed if the expression was false. The
|
|
end of the list is marked by a line containing <CODE>end</CODE>.
|
|
<P>
|
|
|
|
<A NAME="IDX1207"></A>
|
|
<DT><CODE>while</CODE>
|
|
<DD>This command allows to write loops. Its syntax is similar to
|
|
<CODE>if</CODE>: the command takes a single argument, which is an expression
|
|
to evaluate, and must be followed by the commands to execute, one per
|
|
line, terminated by an <CODE>end</CODE>. These commands are called the
|
|
<EM>body</EM> of the loop. The commands in the body of <CODE>while</CODE> are
|
|
executed repeatedly as long as the expression evaluates to true.
|
|
<P>
|
|
|
|
<A NAME="IDX1208"></A>
|
|
<DT><CODE>loop_break</CODE>
|
|
<DD>This command exits the <CODE>while</CODE> loop in whose body it is included.
|
|
Execution of the script continues after that <CODE>while</CODE>s <CODE>end</CODE>
|
|
line.
|
|
<P>
|
|
|
|
<A NAME="IDX1209"></A>
|
|
<DT><CODE>loop_continue</CODE>
|
|
<DD>This command skips the execution of the rest of the body of commands
|
|
in the <CODE>while</CODE> loop in whose body it is included. Execution
|
|
branches to the beginning of the <CODE>while</CODE> loop, where it evaluates
|
|
the controlling expression.
|
|
<P>
|
|
|
|
<A NAME="IDX1210"></A>
|
|
<DT><CODE>end</CODE>
|
|
<DD>Terminate the block of commands that are the body of <CODE>if</CODE>,
|
|
<CODE>else</CODE>, or <CODE>while</CODE> flow-control commands.
|
|
</DL>
|
|
<P>
|
|
|
|
<A NAME="Output"></A>
|
|
<HR SIZE="6">
|
|
<A NAME="SEC233"></A>
|
|
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
|
|
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC232"> < </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> > </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> << </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> Up </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> >> </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
|
</TR></TABLE>
|
|
<H2> 20.4 Commands for Controlled Output </H2>
|
|
<!--docid::SEC233::-->
|
|
<P>
|
|
|
|
During the execution of a command file or a user-defined command, normal
|
|
GDB output is suppressed; the only output that appears is what is
|
|
explicitly printed by the commands in the definition. This section
|
|
describes three commands useful for generating exactly the output you
|
|
want.
|
|
</P><P>
|
|
|
|
<DL COMPACT>
|
|
<A NAME="IDX1211"></A>
|
|
<DT><CODE>echo <VAR>text</VAR></CODE>
|
|
<DD>Print <VAR>text</VAR>. Nonprinting characters can be included in
|
|
<VAR>text</VAR> using C escape sequences, such as <SAMP>`\n'</SAMP> to print a
|
|
newline. <STRONG>No newline is printed unless you specify one.</STRONG>
|
|
In addition to the standard C escape sequences, a backslash followed
|
|
by a space stands for a space. This is useful for displaying a
|
|
string with spaces at the beginning or the end, since leading and
|
|
trailing spaces are otherwise trimmed from all arguments.
|
|
To print <SAMP>` and foo = '</SAMP>, use the command
|
|
<SAMP>`echo \ and foo = \ '</SAMP>.
|
|
<P>
|
|
|
|
A backslash at the end of <VAR>text</VAR> can be used, as in C, to continue
|
|
the command onto subsequent lines. For example,
|
|
</P><P>
|
|
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>echo This is some text\n\
|
|
which is continued\n\
|
|
onto several lines.\n
|
|
</FONT></pre></td></tr></table></P><P>
|
|
|
|
produces the same output as
|
|
</P><P>
|
|
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>echo This is some text\n
|
|
echo which is continued\n
|
|
echo onto several lines.\n
|
|
</FONT></pre></td></tr></table></P><P>
|
|
|
|
<A NAME="IDX1212"></A>
|
|
<DT><CODE>output <VAR>expression</VAR></CODE>
|
|
<DD>Print the value of <VAR>expression</VAR> and nothing but that value: no
|
|
newlines, no <SAMP>`$<VAR>nn</VAR> = '</SAMP>. The value is not entered in the
|
|
value history either. See section <A HREF="gdb_9.html#SEC60">Expressions</A>, for more information
|
|
on expressions.
|
|
<P>
|
|
|
|
<DT><CODE>output/<VAR>fmt</VAR> <VAR>expression</VAR></CODE>
|
|
<DD>Print the value of <VAR>expression</VAR> in format <VAR>fmt</VAR>. You can use
|
|
the same formats as for <CODE>print</CODE>. See section <A HREF="gdb_9.html#SEC63">Output Formats</A>, for more information.
|
|
<P>
|
|
|
|
<A NAME="IDX1213"></A>
|
|
<DT><CODE>printf <VAR>template</VAR>, <VAR>expressions</VAR><small>...</small></CODE>
|
|
<DD>Print the values of one or more <VAR>expressions</VAR> under the control of
|
|
the string <VAR>template</VAR>. To print several values, make
|
|
<VAR>expressions</VAR> be a comma-separated list of individual expressions,
|
|
which may be either numbers or pointers. Their values are printed as
|
|
specified by <VAR>template</VAR>, exactly as a C program would do by
|
|
executing the code below:
|
|
<P>
|
|
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>printf (<VAR>template</VAR>, <VAR>expressions</VAR><small>...</small>);
|
|
</FONT></pre></td></tr></table></P><P>
|
|
|
|
As in <CODE>C</CODE> <CODE>printf</CODE>, ordinary characters in <VAR>template</VAR>
|
|
are printed verbatim, while <EM>conversion specification</EM> introduced
|
|
by the <SAMP>`%'</SAMP> character cause subsequent <VAR>expressions</VAR> to be
|
|
evaluated, their values converted and formatted according to type and
|
|
style information encoded in the conversion specifications, and then
|
|
printed.
|
|
</P><P>
|
|
|
|
For example, you can print two values in hex like this:
|
|
</P><P>
|
|
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
|
|
</FONT></pre></td></tr></table></P><P>
|
|
|
|
<CODE>printf</CODE> supports all the standard <CODE>C</CODE> conversion
|
|
specifications, including the flags and modifiers between the <SAMP>`%'</SAMP>
|
|
character and the conversion letter, with the following exceptions:
|
|
</P><P>
|
|
|
|
<UL>
|
|
<LI>
|
|
The argument-ordering modifiers, such as <SAMP>`2$'</SAMP>, are not supported.
|
|
<P>
|
|
|
|
<LI>
|
|
The modifier <SAMP>`*'</SAMP> is not supported for specifying precision or
|
|
width.
|
|
<P>
|
|
|
|
<LI>
|
|
The <SAMP>`''</SAMP> flag (for separation of digits into groups according to
|
|
<CODE>LC_NUMERIC'</CODE>) is not supported.
|
|
<P>
|
|
|
|
<LI>
|
|
The type modifiers <SAMP>`hh'</SAMP>, <SAMP>`j'</SAMP>, <SAMP>`t'</SAMP>, and <SAMP>`z'</SAMP> are not
|
|
supported.
|
|
<P>
|
|
|
|
<LI>
|
|
The conversion letter <SAMP>`n'</SAMP> (as in <SAMP>`%n'</SAMP>) is not supported.
|
|
<P>
|
|
|
|
<LI>
|
|
The conversion letters <SAMP>`a'</SAMP> and <SAMP>`A'</SAMP> are not supported.
|
|
</UL>
|
|
<P>
|
|
|
|
Note that the <SAMP>`ll'</SAMP> type modifier is supported only if the
|
|
underlying <CODE>C</CODE> implementation used to build GDB supports
|
|
the <CODE>long long int</CODE> type, and the <SAMP>`L'</SAMP> type modifier is
|
|
supported only if <CODE>long double</CODE> type is available.
|
|
</P><P>
|
|
|
|
As in <CODE>C</CODE>, <CODE>printf</CODE> supports simple backslash-escape
|
|
sequences, such as <CODE>\n</CODE>, <SAMP>`\t'</SAMP>, <SAMP>`\\'</SAMP>, <SAMP>`\"'</SAMP>,
|
|
<SAMP>`\a'</SAMP>, and <SAMP>`\f'</SAMP>, that consist of backslash followed by a
|
|
single character. Octal and hexadecimal escape sequences are not
|
|
supported.
|
|
</P><P>
|
|
|
|
Additionally, <CODE>printf</CODE> supports conversion specifications for DFP
|
|
(<EM>Decimal Floating Point</EM>) types using the following length modifiers
|
|
together with a floating point specifier.
|
|
letters:
|
|
</P><P>
|
|
|
|
<UL>
|
|
<LI>
|
|
<SAMP>`H'</SAMP> for printing <CODE>Decimal32</CODE> types.
|
|
<P>
|
|
|
|
<LI>
|
|
<SAMP>`D'</SAMP> for printing <CODE>Decimal64</CODE> types.
|
|
<P>
|
|
|
|
<LI>
|
|
<SAMP>`DD'</SAMP> for printing <CODE>Decimal128</CODE> types.
|
|
</UL>
|
|
<P>
|
|
|
|
If the underlying <CODE>C</CODE> implementation used to build GDB has
|
|
support for the three length modifiers for DFP types, other modifiers
|
|
such as width and precision will also be available for GDB to use.
|
|
</P><P>
|
|
|
|
In case there is no such <CODE>C</CODE> support, no additional modifiers will be
|
|
available and the value will be printed in the standard way.
|
|
</P><P>
|
|
|
|
Here's an example of printing DFP types using the above conversion letters:
|
|
<TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
|
|
</FONT></pre></td></tr></table></P><P>
|
|
|
|
</DL>
|
|
<P>
|
|
|
|
<A NAME="Interpreters"></A>
|
|
<HR SIZE="6">
|
|
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
|
|
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_21.html#SEC229"> << </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_22.html#SEC234"> >> </A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb.html#SEC_Top">Top</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_toc.html#SEC_Contents">Contents</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_38.html#SEC764">Index</A>]</TD>
|
|
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="gdb_abt.html#SEC_About"> ? </A>]</TD>
|
|
</TR></TABLE>
|
|
<BR>
|
|
<FONT SIZE="-1">
|
|
|
|
<address>
|
|
|
|
<p>Please send FSF & GNU inquiries & questions to <a
|
|
href="mailto:gnu@gnu.org">gnu@gnu.org</a>. There are also <a
|
|
href="http://www.gnu.org/home.html#ContactInfo">other ways to
|
|
contact</a> the FSF.</p>
|
|
|
|
<p>These pages are maintained by <a
|
|
href="http://www.gnu.org/software/gdb/">the GDB developers</a>.</p>
|
|
|
|
<p>Copyright Free Software Foundation, Inc., 59 Temple Place - Suite
|
|
330, Boston, MA 02111, USA.</p>
|
|
|
|
<p>Verbatim copying and distribution of this entire article is
|
|
permitted in any medium, provided this notice is preserved.</p>
|
|
|
|
</address>
|
|
|
|
This document was generated
|
|
by <I>GDB Administrator</I> on <I>March, 27 2008</I>
|
|
using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html
|
|
"><I>texi2html</I></A>
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|