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Chapter 9. Examining Source Files

gdb can print parts of your program's source, since the debugging information recorded in the program tells gdb what source files were used to build it. When your program stops, gdb spontaneously prints the line where it stopped. Likewise, when you select a stack frame (refer to Section 8.3 Selecting a frame), gdb prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.

If you use gdb through its gnu Emacs interface, you may prefer to use Emacs facilities to view source; refer to Chapter 25 Using gdb under gnu Emacs.

9.1. Printing source lines

To print lines from a source file, use the list command (abbreviated l). By default, ten lines are printed. There are several ways to specify what part of the file you want to print.

Here are the forms of the list command most commonly used:

list linenum

Print lines centered around line number linenum in the current source file.

list function

Print lines centered around the beginning of function function.

list

Print more lines. If the last lines printed were printed with a list command, this prints lines following the last lines printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (refer to Chapter 8 Examining the Stack), this prints lines centered around that line.

list -

Print lines just before the lines last printed.

By default, gdb prints ten source lines with any of these forms of the list command. You can change this using set listsize:

set listsize count

Make the list command display count source lines (unless the list argument explicitly specifies some other number).

show listsize

Display the number of lines that list prints.

Repeating a list command with [RET] discards the argument, so it is equivalent to typing just list. This is more useful than listing the same lines again. An exception is made for an argument of -; that argument is preserved in repetition so that each repetition moves up in the source file.

In general, the list command expects you to supply zero, one or two linespecs. Linespecs specify source lines; there are several ways of writing them, but the effect is always to specify some source line. Here is a complete description of the possible arguments for list:

list linespec

Print lines centered around the line specified by linespec.

list first,last

Print lines from first to last. Both arguments are linespecs.

list ,last

Print lines ending with last.

list first,

Print lines starting with first.

list +

Print lines just after the lines last printed.

list -

Print lines just before the lines last printed.

list

As described in the preceding table.

Here are the ways of specifying a single source line--all the kinds of linespec.

number

Specifies line number of the current source file. When a list command has two linespecs, this refers to the same source file as the first linespec.

+offset

Specifies the line offset lines after the last line printed. When used as the second linespec in a list command that has two, this specifies the line offset lines down from the first linespec.

-offset

Specifies the line offset lines before the last line printed.

filename:number

Specifies line number in the source file filename.

function

Specifies the line that begins the body of the function function. For example: in C, this is the line with the open brace.

filename:function

Specifies the line of the open-brace that begins the body of the function function in the file filename. You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files.

*address

Specifies the line containing the program address address. address may be any expression.

 
 
  Published under the terms of the GNU General Public License Design by Interspire