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Include header file if it exists to redefine macros in C
What is the difference between #include <filename> and #include “filename”?Why use apparently meaningless do-while and if-else statements in macros?What is the common header format of Python files?In Node.js, how do I “include” functions from my other files?Concatenate multiple files but include filename as section headersHow to fix “Headers already sent” error in PHPHow to pre-compile a C source file without expand the included header file?How to define a macro in a header file from the makefileC includes of includes in headersHow to check if a file exists in Makefile
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I have two header files, one that is a library with a number of default macros defined
i.e:
libraryheader.h:
#define ANAME 1
#define BNAME 2
.
.
.
and I want to be able to have another optional header that the user can supply to redefine these macros in the project
optional.h:
#define ANAME 5
#define BNAME 15
.
.
.
The header optional.h doesn't always exist and I only want to include it if it does exist. Is there a way in the makefile or library header to check if this header exists and redefine the macros.
I'm thinking to check if the file exists in the makefile and set a flag by putting the following in the makefile
ifdef $(test -f optional.h && echo "present")
and then somehow check the flag macro in the library header.
But I haven't had any success yet. Thank you
c makefile header preprocessor
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
add a comment |
I have two header files, one that is a library with a number of default macros defined
i.e:
libraryheader.h:
#define ANAME 1
#define BNAME 2
.
.
.
and I want to be able to have another optional header that the user can supply to redefine these macros in the project
optional.h:
#define ANAME 5
#define BNAME 15
.
.
.
The header optional.h doesn't always exist and I only want to include it if it does exist. Is there a way in the makefile or library header to check if this header exists and redefine the macros.
I'm thinking to check if the file exists in the makefile and set a flag by putting the following in the makefile
ifdef $(test -f optional.h && echo "present")
and then somehow check the flag macro in the library header.
But I haven't had any success yet. Thank you
c makefile header preprocessor
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
1
Well, you could have your makefile update the compile flags to defineHAS_OPTIONAL_Hmacro, and then you can wrap your#includeline in a#ifdef.
– paddy
Mar 26 at 3:46
2
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)
– Matt
Mar 26 at 3:49
add a comment |
I have two header files, one that is a library with a number of default macros defined
i.e:
libraryheader.h:
#define ANAME 1
#define BNAME 2
.
.
.
and I want to be able to have another optional header that the user can supply to redefine these macros in the project
optional.h:
#define ANAME 5
#define BNAME 15
.
.
.
The header optional.h doesn't always exist and I only want to include it if it does exist. Is there a way in the makefile or library header to check if this header exists and redefine the macros.
I'm thinking to check if the file exists in the makefile and set a flag by putting the following in the makefile
ifdef $(test -f optional.h && echo "present")
and then somehow check the flag macro in the library header.
But I haven't had any success yet. Thank you
c makefile header preprocessor
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
I have two header files, one that is a library with a number of default macros defined
i.e:
libraryheader.h:
#define ANAME 1
#define BNAME 2
.
.
.
and I want to be able to have another optional header that the user can supply to redefine these macros in the project
optional.h:
#define ANAME 5
#define BNAME 15
.
.
.
The header optional.h doesn't always exist and I only want to include it if it does exist. Is there a way in the makefile or library header to check if this header exists and redefine the macros.
I'm thinking to check if the file exists in the makefile and set a flag by putting the following in the makefile
ifdef $(test -f optional.h && echo "present")
and then somehow check the flag macro in the library header.
But I haven't had any success yet. Thank you
c makefile header preprocessor
c makefile header preprocessor
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
asked Mar 26 at 3:21
rotalcomorotalcomo
314 bronze badges
314 bronze badges
1
Well, you could have your makefile update the compile flags to defineHAS_OPTIONAL_Hmacro, and then you can wrap your#includeline in a#ifdef.
– paddy
Mar 26 at 3:46
2
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)
– Matt
Mar 26 at 3:49
add a comment |
1
Well, you could have your makefile update the compile flags to defineHAS_OPTIONAL_Hmacro, and then you can wrap your#includeline in a#ifdef.
– paddy
Mar 26 at 3:46
2
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)
– Matt
Mar 26 at 3:49
1
1
Well, you could have your makefile update the compile flags to define
HAS_OPTIONAL_H macro, and then you can wrap your #include line in a #ifdef.– paddy
Mar 26 at 3:46
Well, you could have your makefile update the compile flags to define
HAS_OPTIONAL_H macro, and then you can wrap your #include line in a #ifdef.– paddy
Mar 26 at 3:46
2
2
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)– Matt
Mar 26 at 3:49
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)– Matt
Mar 26 at 3:49
add a comment |
1 Answer
1
active
oldest
votes
As @Matt mentioned in comment "wildcard" can be used.
However, when I tested it using a small program I had to do the following things.
If I include the "optional.h" in my .c file always, then it will give build error when the .h file is not present. Similarly, if I dont include, even if the file is present I will not be able to update the macros. So I did the following in my makefile.
CFLAGS += $(if $(wildcard ./optional.h),-include ./optional.h -DINCLUDE_OPTIONAL_H)
In my .c file I used INCLUDE_OPTIONAL_H for including the optional.h as below.
#ifdef INCLUDE_OPTIONAL_H
#include "optional.h"
#endif
In optional.h, I checked if a macro is already defined and undefined it and then updated it.
#ifdef ANAME
#undef ANAME
#endif
#define ANAME <new_value>
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
add a comment |
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1 Answer
1
active
oldest
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active
oldest
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active
oldest
votes
As @Matt mentioned in comment "wildcard" can be used.
However, when I tested it using a small program I had to do the following things.
If I include the "optional.h" in my .c file always, then it will give build error when the .h file is not present. Similarly, if I dont include, even if the file is present I will not be able to update the macros. So I did the following in my makefile.
CFLAGS += $(if $(wildcard ./optional.h),-include ./optional.h -DINCLUDE_OPTIONAL_H)
In my .c file I used INCLUDE_OPTIONAL_H for including the optional.h as below.
#ifdef INCLUDE_OPTIONAL_H
#include "optional.h"
#endif
In optional.h, I checked if a macro is already defined and undefined it and then updated it.
#ifdef ANAME
#undef ANAME
#endif
#define ANAME <new_value>
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
add a comment |
As @Matt mentioned in comment "wildcard" can be used.
However, when I tested it using a small program I had to do the following things.
If I include the "optional.h" in my .c file always, then it will give build error when the .h file is not present. Similarly, if I dont include, even if the file is present I will not be able to update the macros. So I did the following in my makefile.
CFLAGS += $(if $(wildcard ./optional.h),-include ./optional.h -DINCLUDE_OPTIONAL_H)
In my .c file I used INCLUDE_OPTIONAL_H for including the optional.h as below.
#ifdef INCLUDE_OPTIONAL_H
#include "optional.h"
#endif
In optional.h, I checked if a macro is already defined and undefined it and then updated it.
#ifdef ANAME
#undef ANAME
#endif
#define ANAME <new_value>
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
add a comment |
As @Matt mentioned in comment "wildcard" can be used.
However, when I tested it using a small program I had to do the following things.
If I include the "optional.h" in my .c file always, then it will give build error when the .h file is not present. Similarly, if I dont include, even if the file is present I will not be able to update the macros. So I did the following in my makefile.
CFLAGS += $(if $(wildcard ./optional.h),-include ./optional.h -DINCLUDE_OPTIONAL_H)
In my .c file I used INCLUDE_OPTIONAL_H for including the optional.h as below.
#ifdef INCLUDE_OPTIONAL_H
#include "optional.h"
#endif
In optional.h, I checked if a macro is already defined and undefined it and then updated it.
#ifdef ANAME
#undef ANAME
#endif
#define ANAME <new_value>
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
As @Matt mentioned in comment "wildcard" can be used.
However, when I tested it using a small program I had to do the following things.
If I include the "optional.h" in my .c file always, then it will give build error when the .h file is not present. Similarly, if I dont include, even if the file is present I will not be able to update the macros. So I did the following in my makefile.
CFLAGS += $(if $(wildcard ./optional.h),-include ./optional.h -DINCLUDE_OPTIONAL_H)
In my .c file I used INCLUDE_OPTIONAL_H for including the optional.h as below.
#ifdef INCLUDE_OPTIONAL_H
#include "optional.h"
#endif
In optional.h, I checked if a macro is already defined and undefined it and then updated it.
#ifdef ANAME
#undef ANAME
#endif
#define ANAME <new_value>
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
answered Mar 26 at 4:23
MayurKMayurK
1,4318 silver badges19 bronze badges
1,4318 silver badges19 bronze badges
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
add a comment |
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
Thanks! I wasn't checking the INCLUDE_OPTIONAL_H flag in the right spot.
– rotalcomo
Mar 26 at 4:42
add a comment |
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1
Well, you could have your makefile update the compile flags to define
HAS_OPTIONAL_Hmacro, and then you can wrap your#includeline in a#ifdef.– paddy
Mar 26 at 3:46
2
myprog:CPPFLAGS += $(if $(wildcard optional.h),-include optional.h)– Matt
Mar 26 at 3:49