The debugger can print parts of your program's source, since the debugging information recorded in the program tells the debugger what source files were used to build it. When your program stops, the debugger spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see Selecting a frame: Selection.), the debugger prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use the debugger through its GNU Emacs interface, you may prefer to use Emacs facilities to view source.
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:
Print lines centered around line number linenum in the current source file.
Print lines centered around the beginning of function function.
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 (see Chapter 12: Stack.), this prints lines centered around that line.
Print lines just before the lines last printed.
By default, the debugger prints ten source lines with any of these forms of the list command. You can change this using set listsize:
Make the list command display count source lines (unless the list argument explicitly specifies some other number).
Display the number of lines that list prints.
Repeating a list command with Enter 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:
Print lines centered around the line specified by linespec.
Print lines from first to last. Both arguments are linespecs.
Print lines ending with last.
Print lines starting with first.
Print lines just after the lines last printed.
Print lines just before the lines last printed.
As described in the preceding table.
Here are the ways of specifying a single source line — all the kinds of linespec.
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.
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.
Specifies the line offset lines before the last line printed.
Specifies line number in the source file filename.
Specifies the line that begins the body of the function function. For example: in C, this is the line with the open brace.
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.
Specifies the line containing the program address address. address may be any expression.