mirror of
https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-28 06:13:31 +01:00
lib/cc: Define the standard C macro pasting trick in one place.
This file is a workaround for the issue that if you say `a ## b` to create a token that is the name of a macro, the C preprocessor won't expand that macro. So you can't say this: #define FOO__SQUARE(x) ((x)*(x)) #define FOO__CUBE(x) ((x)*(x)*(x)) #define FOO(func, x) FOO__##func(x) Instead, the standard C trick is to add a layer of indirection: #define PASTE(a,b) PASTE__(a,b) #define PASTE__(a,b) a ## b #define FOO__SQUARE(x) ((x)*(x)) #define FOO__CUBE(x) ((x)*(x)*(x)) #define FOO(func, x) PASTE(FOO__, func)(x) We should use this kind of trick sparingly, since it gets confusing.
This commit is contained in:
parent
45698e89ed
commit
4541a59019
@ -3,4 +3,5 @@
|
||||
noinst_HEADERS += \
|
||||
src/lib/cc/compat_compiler.h \
|
||||
src/lib/cc/ctassert.h \
|
||||
src/lib/cc/tokpaste.h \
|
||||
src/lib/cc/torint.h
|
||||
|
30
src/lib/cc/tokpaste.h
Normal file
30
src/lib/cc/tokpaste.h
Normal file
@ -0,0 +1,30 @@
|
||||
/* Copyright (c) 2001 Matej Pfajfar.
|
||||
* Copyright (c) 2001-2004, Roger Dingledine.
|
||||
* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
|
||||
* Copyright (c) 2007-2019, The Tor Project, Inc. */
|
||||
/* See LICENSE for licensing information */
|
||||
|
||||
/**
|
||||
* @file tokpaste.h
|
||||
* @brief Token-pasting macros.
|
||||
**/
|
||||
|
||||
#ifndef TOR_LIB_CC_TOKPASTE_H
|
||||
#define TOR_LIB_CC_TOKPASTE_H
|
||||
|
||||
/**
|
||||
* Concatenate `a` and `b` in a way that allows their result itself to be
|
||||
* expanded by the preprocessor.
|
||||
*
|
||||
* Ordinarily you could just say `a ## b` in a macro definition. But doing so
|
||||
* results in a symbol which the preprocessor will not then expand. If you
|
||||
* wanted to use `a ## b` to create the name of a macro and have the
|
||||
* preprocessor expand _that_ macro, you need to have another level of
|
||||
* indirection, as this macro provides.
|
||||
**/
|
||||
#define PASTE(a,b) PASTE__(a,b)
|
||||
|
||||
/** Helper for PASTE(). */
|
||||
#define PASTE__(a,b) a ## b
|
||||
|
||||
#endif /* !defined(TOR_LIB_CC_TOKPASTE_H) */
|
Loading…
Reference in New Issue
Block a user