Red Hat ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE, Руководство пользователя

Страница: 99 / 410

Chapter 11.
C Preprocessor Macros
Some languages, such as C and C++, provide a way to define and invoke "preprocessor macros" which
expand into strings of tokens. gdb can evaluate expressions containing macro invocations, show the
result of macro expansion, and show a macro’s definition, including where it was defined.
You may need to compile your program specially to provide gdb with information about preproces-
sor macros. Most compilers do not include macros in their debugging information, even when you
compile with the
-g
flag. Refer to Section 6.1 Compiling for debugging .
A program may define a macro at one point, remove that definition later, and then provide a different
definition after that. Thus, at different points in the program, a macro may have different definitions, or
have no definition at all. If there is a current stack frame, gdb uses the macros in scope at that frame’s
source code line. Otherwise, gdb uses the macros in scope at the current listing location; (refer to
Section 9.1 Printing source lines .
At the moment, gdb does not support the
##
token-splicing operator, the
#
stringification operator, or
variable-arity macros.
Whenever gdb evaluates an expression, it always expands any macro invocations present in the ex-
pression. gdb also provides the following commands for working with macros explicitly.
macro expand
expression
macro exp
expression
Show the results of expanding all preprocessor macro invocations in
expression
. Since gdb
simply expands macros, but does not parse the result,
expression
need not be a valid expres-
sion; it can be any string of tokens.
macro expand-once
expression
macro exp1
expression
(This command is not yet implemented.) Show the results of expanding those preprocessor macro
invocations that appear explicitly in
expression
. Macro invocations appearing in that expan-
sion are left unchanged. This command allows you to see the effect of a particular macro more
clearly, without being confused by further expansions. Since gdb simply expands macros, but
does not parse the result,
expression
need not be a valid expression; it can be any string of
tokens.
info macro
macro
Show the definition of the macro named
macro
, and describe the source location where that
definition was established.
macro define
macro replacement-list
macro define
macro
(
arglist
)
replacement-list
(This command is not yet implemented.) Introduce a definition for a preprocessor macro named
macro
, invocations of which are replaced by the tokens given in
replacement-list
. The first
form of this command defines an "object-like" macro, which takes no arguments; the second
form defines a "function-like" macro, which takes the arguments given in
arglist
.
A definition introduced by this command is in scope in every expression evaluated in gdb, until
it is removed with the
macro undef
command, described below. The definition overrides all