2002-09-20 Kevin Buettner <kevinb@redhat.com>
From Eli Zaretskii <eliz@is.elta.co.il>: * gdb.texinfo (Character Sets): Use @smallexample instead of @example. Use GNU/Linux instead of Linux. 2002-09-20 Jim Blandy <jimb@redhat.com> * gdb.texinfo: Add character set documentation.
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@ -1,3 +1,13 @@
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2002-09-20 Kevin Buettner <kevinb@redhat.com>
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From Eli Zaretskii <eliz@is.elta.co.il>:
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* gdb.texinfo (Character Sets): Use @smallexample instead of
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@example. Use GNU/Linux instead of Linux.
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2002-09-20 Jim Blandy <jimb@redhat.com>
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* gdb.texinfo: Add character set documentation.
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2002-09-19 Andrew Cagney <ac131313@redhat.com>
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* gdb.texinfo (Packets): Revise `z' and `Z' packet documentation.
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@ -4493,6 +4493,8 @@ Table}.
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* Vector Unit:: Vector Unit
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* Memory Region Attributes:: Memory region attributes
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* Dump/Restore Files:: Copy between memory and a file
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* Character Sets:: Debugging programs that use a different
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character set than GDB does
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@end menu
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@node Expressions
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@ -5879,6 +5881,254 @@ the @var{bias} argument is applied.
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@end table
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@node Character Sets
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@section Character Sets
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@cindex character sets
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@cindex charset
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@cindex translating between character sets
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@cindex host character set
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@cindex target character set
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If the program you are debugging uses a different character set to
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represent characters and strings than the one @value{GDBN} uses itself,
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@value{GDBN} can automatically translate between the character sets for
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you. The character set @value{GDBN} uses we call the @dfn{host
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character set}; the one the inferior program uses we call the
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@dfn{target character set}.
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For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
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uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
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remote protocol (@pxref{Remote,Remote Debugging}) to debug a program
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running on an IBM mainframe, which uses the @sc{ebcdic} character set,
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then the host character set is Latin-1, and the target character set is
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@sc{ebcdic}. If you give @value{GDBN} the command @code{set
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target-charset ebcdic-us}, then @value{GDBN} translates between
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@sc{ebcdic} and Latin 1 as you print character or string values, or use
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character and string literals in expressions.
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@value{GDBN} has no way to automatically recognize which character set
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the inferior program uses; you must tell it, using the @code{set
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target-charset} command, described below.
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Here are the commands for controlling @value{GDBN}'s character set
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support:
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@table @code
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@item set target-charset @var{charset}
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@kindex set target-charset
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Set the current target character set to @var{charset}. We list the
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character set names @value{GDBN} recognizes below, but if you invoke the
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@code{set target-charset} command with no argument, @value{GDBN} lists
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the character sets it supports.
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@end table
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@table @code
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@item set host-charset @var{charset}
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@kindex set host-charset
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Set the current host character set to @var{charset}.
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By default, @value{GDBN} uses a host character set appropriate to the
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system it is running on; you can override that default using the
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@code{set host-charset} command.
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@value{GDBN} can only use certain character sets as its host character
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set. We list the character set names @value{GDBN} recognizes below, and
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indicate which can be host character sets, but if you invoke the
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@code{set host-charset} command with no argument, @value{GDBN} lists the
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character sets it supports, placing an asterisk (@samp{*}) after those
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it can use as a host character set.
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@item set charset @var{charset}
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@kindex set charset
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Set the current host and target character sets to @var{charset}. If you
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invoke the @code{set charset} command with no argument, it lists the
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character sets it supports. @value{GDBN} can only use certain character
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sets as its host character set; it marks those in the list with an
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asterisk (@samp{*}).
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@item show charset
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@itemx show host-charset
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@itemx show target-charset
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@kindex show charset
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@kindex show host-charset
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@kindex show target-charset
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Show the current host and target charsets. The @code{show host-charset}
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and @code{show target-charset} commands are synonyms for @code{show
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charset}.
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@end table
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@value{GDBN} currently includes support for the following character
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sets:
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@table @code
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@item ASCII
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@cindex ASCII character set
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Seven-bit U.S. @sc{ascii}. @value{GDBN} can use this as its host
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character set.
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@item ISO-8859-1
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@cindex ISO 8859-1 character set
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@cindex ISO Latin 1 character set
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The ISO Latin 1 character set. This extends ASCII with accented
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characters needed for French, German, and Spanish. @value{GDBN} can use
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this as its host character set.
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@item EBCDIC-US
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@itemx IBM1047
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@cindex EBCDIC character set
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@cindex IBM1047 character set
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Variants of the @sc{ebcdic} character set, used on some of IBM's
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mainframe operating systems. (@sc{gnu}/Linux on the S/390 uses U.S. @sc{ascii}.)
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@value{GDBN} cannot use these as its host character set.
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@end table
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Note that these are all single-byte character sets. More work inside
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GDB is needed to support multi-byte or variable-width character
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encodings, like the UTF-8 and UCS-2 encodings of Unicode.
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Here is an example of @value{GDBN}'s character set support in action.
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Assume that the following source code has been placed in the file
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@file{charset-test.c}:
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@smallexample
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#include <stdio.h>
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char ascii_hello[]
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= @{72, 101, 108, 108, 111, 44, 32, 119,
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111, 114, 108, 100, 33, 10, 0@};
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char ibm1047_hello[]
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= @{200, 133, 147, 147, 150, 107, 64, 166,
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150, 153, 147, 132, 90, 37, 0@};
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main ()
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@{
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printf ("Hello, world!\n");
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@}
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@end example
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In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
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containing the string @samp{Hello, world!} followed by a newline,
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encoded in the @sc{ascii} and @sc{ibm1047} character sets.
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We compile the program, and invoke the debugger on it:
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@smallexample
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$ gcc -g charset-test.c -o charset-test
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$ gdb -nw charset-test
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GNU gdb 2001-12-19-cvs
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Copyright 2001 Free Software Foundation, Inc.
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@dots{}
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(gdb)
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@end example
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We can use the @code{show charset} command to see what character sets
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@value{GDBN} is currently using to interpret and display characters and
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strings:
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@smallexample
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(gdb) show charset
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The current host and target character set is `iso-8859-1'.
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(gdb)
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@end example
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For the sake of printing this manual, let's use @sc{ascii} as our
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initial character set:
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@smallexample
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(gdb) set charset ascii
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(gdb) show charset
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The current host and target character set is `ascii'.
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(gdb)
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@end example
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Let's assume that @sc{ascii} is indeed the correct character set for our
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host system --- in other words, let's assume that if @value{GDBN} prints
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characters using the @sc{ascii} character set, our terminal will display
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them properly. Since our current target character set is also
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@sc{ascii}, the contents of @code{ascii_hello} print legibly:
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@smallexample
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(gdb) print ascii_hello
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$1 = 0x401698 "Hello, world!\n"
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(gdb) print ascii_hello[0]
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$2 = 72 'H'
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(gdb)
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@end example
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@value{GDBN} uses the target character set for character and string
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literals you use in expressions:
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@smallexample
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(gdb) print '+'
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$3 = 43 '+'
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(gdb)
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@end example
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The @sc{ascii} character set uses the number 43 to encode the @samp{+}
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character.
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@value{GDBN} relies on the user to tell it which character set the
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target program uses. If we print @code{ibm1047_hello} while our target
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character set is still @sc{ascii}, we get jibberish:
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@smallexample
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(gdb) print ibm1047_hello
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$4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
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(gdb) print ibm1047_hello[0]
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$5 = 200 '\310'
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(gdb)
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@end example
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If we invoke the @code{set target-charset} command without an argument,
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@value{GDBN} tells us the character sets it supports:
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@smallexample
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(gdb) set target-charset
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Valid character sets are:
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ascii *
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iso-8859-1 *
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ebcdic-us
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ibm1047
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* - can be used as a host character set
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@end example
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We can select @sc{ibm1047} as our target character set, and examine the
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program's strings again. Now the @sc{ascii} string is wrong, but
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@value{GDBN} translates the contents of @code{ibm1047_hello} from the
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target character set, @sc{ibm1047}, to the host character set,
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@sc{ascii}, and they display correctly:
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@smallexample
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(gdb) set target-charset ibm1047
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(gdb) show charset
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The current host character set is `ascii'.
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The current target character set is `ibm1047'.
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(gdb) print ascii_hello
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$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
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(gdb) print ascii_hello[0]
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$7 = 72 '\110'
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(gdb) print ibm1047_hello
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$8 = 0x4016a8 "Hello, world!\n"
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(gdb) print ibm1047_hello[0]
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$9 = 200 'H'
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(gdb)
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@end example
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As above, @value{GDBN} uses the target character set for character and
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string literals you use in expressions:
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@smallexample
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(gdb) print '+'
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$10 = 78 '+'
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(gdb)
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@end example
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The IBM1047 character set uses the number 78 to encode the @samp{+}
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character.
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@node Macros
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@chapter C Preprocessor Macros
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