Purpose of _LINUX_EXPORT_H macro
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What is the purpose of defining _LINUX_EXPORT_H in include/linux/export.h? It seems to be defined in this file and never referenced anywhere else. Is it redundant?
Link: _LINUX_EXPORT_H in torvalds/linux on github
linux kernel c
asked Mar 3 at 1:26
MartinMartin
111
add a comment |
What is the purpose of defining _LINUX_EXPORT_H in include/linux/export.h? It seems to be defined in this file and never referenced anywhere else. Is it redundant?
Link: _LINUX_EXPORT_H in torvalds/linux on github
linux kernel c
asked Mar 3 at 1:26
MartinMartin
111
5
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
1
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04
add a comment |
What is the purpose of defining _LINUX_EXPORT_H in include/linux/export.h? It seems to be defined in this file and never referenced anywhere else. Is it redundant?
Link: _LINUX_EXPORT_H in torvalds/linux on github
linux kernel c
asked Mar 3 at 1:26
MartinMartin
111
What is the purpose of defining _LINUX_EXPORT_H in include/linux/export.h? It seems to be defined in this file and never referenced anywhere else. Is it redundant?
Link: _LINUX_EXPORT_H in torvalds/linux on github
linux kernel c
linux kernel c
asked Mar 3 at 1:26
MartinMartin
111
asked Mar 3 at 1:26
MartinMartin
111
asked Mar 3 at 1:26
MartinMartin
111
asked Mar 3 at 1:26
MartinMartin
111
asked Mar 3 at 1:26
MartinMartin
111
111
5
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
1
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04
add a comment |
5
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
1
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04
5
5
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
1
1
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04
add a comment |
1 Answer
1
active
oldest
votes
If you look carefully at the file, it starts and ends with these lines:
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
...
#endif /* _LINUX_EXPORT_H */
These lines mean that if the file is included twice (either through a mistake or through including another file that includes this file) then the second time around the value is defined, and so the whole file is effectively skipped.
These are commonly known as "header guards" or "include guards" and you'll note that many of the standard include files use this pattern; e.g pwd.h has
#ifndef _PWD_H
#define _PWD_H 1
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
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
If you look carefully at the file, it starts and ends with these lines:
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
...
#endif /* _LINUX_EXPORT_H */
These lines mean that if the file is included twice (either through a mistake or through including another file that includes this file) then the second time around the value is defined, and so the whole file is effectively skipped.
These are commonly known as "header guards" or "include guards" and you'll note that many of the standard include files use this pattern; e.g pwd.h has
#ifndef _PWD_H
#define _PWD_H 1
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
add a comment |
If you look carefully at the file, it starts and ends with these lines:
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
...
#endif /* _LINUX_EXPORT_H */
These lines mean that if the file is included twice (either through a mistake or through including another file that includes this file) then the second time around the value is defined, and so the whole file is effectively skipped.
These are commonly known as "header guards" or "include guards" and you'll note that many of the standard include files use this pattern; e.g pwd.h has
#ifndef _PWD_H
#define _PWD_H 1
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
add a comment |
If you look carefully at the file, it starts and ends with these lines:
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
...
#endif /* _LINUX_EXPORT_H */
These lines mean that if the file is included twice (either through a mistake or through including another file that includes this file) then the second time around the value is defined, and so the whole file is effectively skipped.
These are commonly known as "header guards" or "include guards" and you'll note that many of the standard include files use this pattern; e.g pwd.h has
#ifndef _PWD_H
#define _PWD_H 1
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
If you look carefully at the file, it starts and ends with these lines:
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
...
#endif /* _LINUX_EXPORT_H */
These lines mean that if the file is included twice (either through a mistake or through including another file that includes this file) then the second time around the value is defined, and so the whole file is effectively skipped.
These are commonly known as "header guards" or "include guards" and you'll note that many of the standard include files use this pattern; e.g pwd.h has
#ifndef _PWD_H
#define _PWD_H 1
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
edited Mar 3 at 14:23
Kusalananda♦
138k17258428
138k17258428
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
answered Mar 3 at 14:21
Stephen HarrisStephen Harris
27.1k35283
27.1k35283
add a comment |
add a comment |
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5
Are you asking about the purpose of include guards?
– steeldriver
Mar 3 at 1:39
1
It appears that the questioner is asking for the purpose of that macro not knowing that it is an include guard.
– JdeBP
Mar 3 at 7:04