What does an empty # mean in a macro definition?
I have the following macro:
#define F(Args, ...)
// macro definition
#
F(()) // looks like usage?
#undef F
What does the line containing only # mean? Is F(()) a usage of the macro?
c++ c macros
edited Feb 2 at 14:02
Boann
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
add a comment |
I have the following macro:
#define F(Args, ...)
// macro definition
#
F(()) // looks like usage?
#undef F
What does the line containing only # mean? Is F(()) a usage of the macro?
c++ c macros
edited Feb 2 at 14:02
Boann
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
add a comment |
I have the following macro:
#define F(Args, ...)
// macro definition
#
F(()) // looks like usage?
#undef F
What does the line containing only # mean? Is F(()) a usage of the macro?
c++ c macros
edited Feb 2 at 14:02
Boann
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
I have the following macro:
#define F(Args, ...)
// macro definition
#
F(()) // looks like usage?
#undef F
What does the line containing only # mean? Is F(()) a usage of the macro?
c++ c macros
c++ c macros
edited Feb 2 at 14:02
Boann
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
edited Feb 2 at 14:02
Boann
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
edited Feb 2 at 14:02
Boann
37.3k1290121
edited Feb 2 at 14:02
Boann
37.3k1290121
edited Feb 2 at 14:02
Boann
37.3k1290121
37.3k1290121
asked Feb 2 at 10:03
embedcembedc
35910
asked Feb 2 at 10:03
embedcembedc
35910
asked Feb 2 at 10:03
embedcembedc
35910
35910
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Technically, that's not part of the macro (no continuation line before it).
It's a directive that comes after the #define directive.
# on its own line is called a null directive and it does nothing (as good as a comment).
It's no longer practically useful (except as a visual marker) but in prehistoric C, the preprocessor only got invoked if a C source file started with a directive and the null directive placed at the very beginning of a C file was a good way to make sure the file was preprocessed (i.e., that later directives worked) without starting with a concrete directive.
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Technically, that's not part of the macro (no continuation line before it).
It's a directive that comes after the #define directive.
# on its own line is called a null directive and it does nothing (as good as a comment).
It's no longer practically useful (except as a visual marker) but in prehistoric C, the preprocessor only got invoked if a C source file started with a directive and the null directive placed at the very beginning of a C file was a good way to make sure the file was preprocessed (i.e., that later directives worked) without starting with a concrete directive.
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
add a comment |
Technically, that's not part of the macro (no continuation line before it).
It's a directive that comes after the #define directive.
# on its own line is called a null directive and it does nothing (as good as a comment).
It's no longer practically useful (except as a visual marker) but in prehistoric C, the preprocessor only got invoked if a C source file started with a directive and the null directive placed at the very beginning of a C file was a good way to make sure the file was preprocessed (i.e., that later directives worked) without starting with a concrete directive.
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
add a comment |
Technically, that's not part of the macro (no continuation line before it).
It's a directive that comes after the #define directive.
# on its own line is called a null directive and it does nothing (as good as a comment).
It's no longer practically useful (except as a visual marker) but in prehistoric C, the preprocessor only got invoked if a C source file started with a directive and the null directive placed at the very beginning of a C file was a good way to make sure the file was preprocessed (i.e., that later directives worked) without starting with a concrete directive.
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
Technically, that's not part of the macro (no continuation line before it).
It's a directive that comes after the #define directive.
# on its own line is called a null directive and it does nothing (as good as a comment).
It's no longer practically useful (except as a visual marker) but in prehistoric C, the preprocessor only got invoked if a C source file started with a directive and the null directive placed at the very beginning of a C file was a good way to make sure the file was preprocessed (i.e., that later directives worked) without starting with a concrete directive.
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
edited Feb 2 at 10:22
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
answered Feb 2 at 10:10
PSkocikPSkocik
34.5k65578
34.5k65578
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
add a comment |
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
I suppose it can be used to obfuscade code even further
– Stack Danny
Feb 2 at 12:01
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
@StackDanny Yeah, it could be seen as unnecessarily obfuscating.
– PSkocik
Feb 2 at 12:08
2
2
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
I knew that preprocessing was not always an automatic part of C compilation, but I didn't know that this was how the preprocessor was engaged. Nice.
– John Bollinger
Feb 2 at 14:54
add a comment |
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