dbx.1

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quotation marks, as shown:
.EX
(dbx) trace "source_file.c":17 
.EE
The example specifies tracing line 17 in 
.PN source_file.c.
.IP 
If you specify an expression at a source line number, 
.PN dbx
displays the value of the expression when it executes the source line.
.IP 
Specifying a variable name causes
.PN dbx
to display the name and value of the variable each time it changes.
Program execution is substantially slower during this form of tracing.
.IP 
The \fIcondition\fP argument is a Boolean expression 
that
.PN dbx
evaluates prior to displaying any tracing information;
if the condition is false,
.PN dbx
does not display the information.  
.IP
If you omit the arguments to the
.B trace
command, 
.PN dbx
displays each source line before executing it.
Program execution is substantially slower during this form of tracing.
.SS Printing Variables and Expressions
.NXR "variable" "displaying the value of with dbx"
The
.PN dbx
debugger allows you to display the value of your program's variables and
expressions.  This section describes how the debugger resolves ambiguous
names, how you specify expressions, and the commands that you use to
display the value of variables and expressions.
.PP
The debugger resolves names by first searching for the name in the
static scope of the current procedure or function.  If no name is defined in the
static scope, the debugger searches the dynamic scope. If neither scope
yields a defined name, the debugger chooses an arbitrary symbol and
displays the following message:
.EX
[using\ \fIqualified\.name\fP]
.EE
The debugger substitutes the qualified name of the arbitrary symbol for
\fIqualified.name\fP in the message.
.PP
You can override this name resolution procedure by qualifying 
identifiers with a block name, as in \fImodule\fP.\fIvariable\fP. 
For the C language, the debugger treats a source file as a module named
for the filename without the
.PN .c 
suffix.
.PP
You specify
.PN dbx
expressions using the C or Pascal syntax for expressions. The debugger
supports a subset of the expression syntax for both languages; that is,
the debugger supports the syntax that is common between the two
languages.
.PP
In some cases, the debugger supports the syntax of either C or Pascal.
For example, you can denote indirection using either an asterisk (*)
as a prefix or a circumflex (^) as a suffix.
You can use the field reference operator (.) with pointers
as well as records or structures, making the C operator (->) unnecessary
(although it is supported). To specify a hexadecimal value, precede the
value with the "0x" characters.
.PP
You must enclose array expressions in brackets ([ ]). 
.PP
The debugger checks the type of each expression;
you can override the type of an expression 
by using (\fIexpression\fR)\\\fItype-name\fP. 
.PP 
You can also specify a register name in an expression.
.NX R "vector register" 
You denote registers by \fB$r\fIN\fR where \fIN\fR is the number of the register.
You denote vector registers as follows:
.IP "\fB$v\fIN\fR[\fIK\fR]"
Denotes a vector data register where \fIN\fR is the register number and 
\fIK\fR is an index. The debugger treats each data register as a
double-precision floating point array of 64
elements, indexed from 0 to 63.
.IP "\fB$vaer\fR"
Denotes the vector arithmetic error register, which 
.PN dbx
treats as a longword.
.IP "\fB$vcr\fR"
Denotes the longword vector count register.
.IP "\fB$vlr\fR"
Denotes the longword vector length register
.IP "\fB$vmr\fR"
Denotes the vector mask register. The debugger treats the \fB$vmr\fR as a Boolean
array of 64 elements, indexed from 0 to 63.
.PP
For more information about VAX registers, see the \fIVAX Architecture
Manual\fP.
.PP
The following list describes the debugger commands for printing
variables and expressions:
.IP "\fBassign\fP \fIvariable\fP \fB=\fP \fIexpression\fP" 
.ns
.IP "\fBassign\fP \fIvector-register\fP \fB= ""\fIvalue\fP [\fB,\fIvalue\fP]"""
.NX R "assign command (dbx)"
Assigns the value of the expression to the variable or stores the
specified value in the specified vector register.
.IP
The
.B assign
command allows you to assign a value to one element of a vector
register. (You cannot use the command to assign a value to a nonvector
register.) You can change only one element in a register in a single
command. If you omit the second \fIvalue\fP, 
.PN dbx
decodes the first \fIvalue\fP into the first half of the register. If you
specify both values, the debugger decodes the first \fIvalue\fP into the first
half of the register and the second \fIvalue\fP into the second half of the
register.
.IP
The \fIvalue\fP can be an integer, floating point, or hexadecimal
value.
.IP "\fBdump\fP [\fIprocedure\fR] [\fB>\fP \fIfilename\fP]"
.NX R "dump command (dbx)"
Displays the names and values of variables in the given procedure
or the current one if none is specified.
If you specify the dot (.),
the debugger prints the values of all active variables.
.IP "\fBprint\fP \fIexpression\fP [\fB,\fP \fIexpression\fP ...]"
.NX R "print command (dbx)"
Displays the values of the specified expressions.
.IP "\fBwhatis\fP \fIname\fP"
.NX R "whatis command (dbx)"
Displays the declaration of the given name, which you can qualify 
using a block name. 
.IP "\fBup\fP [\fIcount\fP]"
.ns
.IP "\fBdown\fP [\fIcount\fP]"
.NX R "up command (dbx)"
.NX R "down command (dbx)"
Moves the current procedure or function, which is used for resolving names,
up or down the stack \fIcount\fP levels.
The default for \fIcount\fP is 1.
.IP \fBwhere\fP
.NX R "where command (dbx)"
Displays a list of the active procedures and functions.
.IP "\fBwhereis\fP \fIidentifier\fP"
.NX R "whereis command (dbx)"
Displays the full qualification of all the symbols whose
name matches the given identifier.
The order in which 
.PN dbx
displays the symbols is not meaningful.
.IP "\fBwhich\fP \fIidentifier\fP"
.NX R "which command (dbx)"
Displays the full qualification of the given identifier; that is, display
the outer blocks that are associated with the identifier.
.SS Accessing Source Files
You can use the following
.PN dbx
commands to access source files during a debugging session:
.IP "/\fIregular\ expression\fP[/]" 
.ns
.IP "?\fIregular\ expression\fP[?]"
Searches forward or backward in the current source file
for the given pattern. For information on specifying a regular
expression, see \fIThe Big Gray Book: The Next Step with ULTRIX\fP.
.IP "\fBcd\fP [\fIdirname\fP]"
.NX R "cd command (dbx)"
Changes the current directory to the directory you specify. If you omit
the \fIdirname\fP argument,
.PN dbx
uses the directory specified in the HOME environment variable as the
current directory.
.IP "\fBedit\fP [\fIfilename\fP]"
.ns
.IP "\fBedit\fP \fIprocedure/function\fP"
.NX R "edit command (dbx)"
Invokes an editor on \fIfilename\fP or the current source file if none
is specified.
If you specify a procedure or function name,
the editor reads in the file that contains that procedure or function.
Which editor is invoked by default depends on the installation.
You can override the default setting by modifying the EDITOR environment
variable.
.IP "\fBfile\fP [\fIfilename\fP]"
.NX R "file command (dbx)"
Changes the current source file name to \fIfilename\fP.
If you omit \fIfilename\fP, 
.PN dbx
displays the name of the current source file.
.IP "\fBfunc\fP [\fIprocedure/function\fP]"
Changes the current procedure or function.
If you omit \fIprocedure/function\fP, 
.PN dbx
displays the current procedure or function.
Changing the current procedure or function implicitly changes the current source file
to the one that contains the procedure or function; it also changes the current scope
used for name resolution.
.IP "\fBlist\fP [\fIsource-line-number\fP [\fB,\fP \fIsource-line-number\fP]]"
.ns
.IP "\fBlist\fP [\fIsource-line-number\fP : \fIinteger\fP]
.ns
.IP "\fBlist\fP [\fIprocedure/function\fP]"
.NX R "list command (dbx)"
Lists the lines in the current source file from the first line number you
specify to the second one you specify, inclusive.
If you omit the second \fIsource-line-number\fP argument, 
.PN dbx
begins at the first line number and displays the next 10 lines. If you omit both arguments, 
.PN dbx
begins the display at the current source line and displays 10 lines.
.IP 
If you specify a source line number, a colon, and an integer, 
.PN dbx 
lists lines in the current source file starting from \fIsource-line-number\fP
and continuing for \fIinteger\fP number of lines.
.IP
If you specify the name of a procedure or function,
lines \fIn-k\fP to \fIn+k\fP are listed, where \fIn\fP is the first statement
in the procedure or function and \fIk\fP is equal to the 
.B $listwindow
variable. The default value of 
.B $listwindow 
is 10.
.IP "\fBpwd\fP"
.NX R "pwd command (dbx)"
Displays the pathname of the current directory.
.IP "\fBuse\fP \fIpathname pathname...\fP"
.NX R "use command (dbx)"
Sets the list of directories that 
.PN dbx
searches when looking for source files. You can specify either a full or
relative pathname for \fIpathname\fR.
.SS Command Aliases and Variables
The debugger allows you to define aliases and set variables to make your
debugging sessions more efficient. The following list describes the commands
you use to perform these tasks:
.IP "\fBalias\fP \fIname\fP \fIcommand\fP"
.ns
.IP "\fBalias\fP \fIname\fP \fR[\fB(\fIparameters\fB)\fR] \fIstring\fP"
.NX R "alias command (dbx)"
Lists existing aliases or defines an alias for a 
.PN dbx
command or a string. Specify the alias name in the \fIname\fR argument
and the 
.PN dbx
command or string in the \fIcommand\fR or \fIstring\fR argument. You can
define an alias that accepts parameters by specifying the
\fIparameters\fR argument.
For example,
to define an alias rr for the command 
.BR rerun ,
enter the following command:
.EX 
(dbx) alias rr rerun
.EE 
To define halt as an alias that sets a stop at a particular line,
issue the following command:
.EX 
(dbx) alias halt(x) "stop at x"
.EE 
Once you issue this command,
.PN dbx
interprets the following commands as equivalent:
.EX
(dbx) halt(12)
(dbx) stop at 12
.EE
Both commands create a stop event at line 12.
.IP "\fBgetenv \fIname\fP"
.NX R "getenv command (dbx)"
Displays the value of the environment variable, \fIname\fP.
.IP "\fBsetenv \fIname value\fP"
.NX R "setenv command (dbx)"
Sets the environment variable \fIname\fP to \fIvalue\fP by changing the
value of an existing environment variable or creating a new one.
.IP "\fBset\fP \fR[\fIname\fP [= \fIexpression\fP]\fR]"
.NX R "set command (dbx)"
Lists existing debugger variables and their values or defines a value
for the named variable. 
.IP
Some debugger variables contain either a zero or nonzero value that
controls
.PN dbx
behavior. For example, when set to a nonzero value, the 
.B $hexstrings
variable causes the debugger to display all strings in hexadecimal
format. When set to zero, the variable causes the debugger to display
strings in character format. You can set a variable like the 
.B $hexstrings
variable to a nonzero value as shown:
.EX
(dbx) set $hexstrings 
.EE
You can disable the variable using the
.B unset
command, as shown:
.EX
(dbx) unset $hexstrings
.EE
.IP
You can use the 
.B set
command to create 
variables using a name of your own. Variables you create must
not begin with a dollar sign ($), and the name of the variable must not
conflict with names in the program
you are debugging. When you create a variable, the
.B set
command
treats \fIexpression\fR as an address and creates a variable at the
specified address. You can use the variable name in 
.B trace
and
.B stop
commands to control program execution.
.IP
The following list describes the debugger variables: 
.RS
.IP "$frame" 
If you set this variable to an address, 
.PN dbx
uses the stack frame at that address 
for stack traces and for accessing local variables.
This variable is particularly useful for kernel debugging.
.IP "$hexchars" 
.ns
.IP "$hexints"
.ns
.IP "$hexoffsets"
.ns
.IP "$hexstrings"
You can set these variables to cause 
.PN dbx
to display 
character strings, integers, offsets from registers, or character pointers,
respectively, in hexadecimal format.
.IP "$historywindow"
The value of this variable determines the number of commands 
.PN dbx
stores in the history list.  By default, the history list contains 20
commands.
.IP "$listwindow"
The value of this variable determines the number