Why can't I explicitly `-I /usr/include`?
Both gcc and clang seem to silently discard /usr/include from the list of include directories when explicitly included via -I.
Is there a specific reason as to why common compilers apparently don't allow to include the system's include dir?
background:
Suppose you depend on a header file located in /usr/include while having inherited a directory containing an incompatible version of the same header from your build system via the CPATH environment variable (effectively appending that directory to the -I list from the right).
gcc include clang
asked Nov 22 at 20:40
vega8
5071320
add a comment |
Both gcc and clang seem to silently discard /usr/include from the list of include directories when explicitly included via -I.
Is there a specific reason as to why common compilers apparently don't allow to include the system's include dir?
background:
Suppose you depend on a header file located in /usr/include while having inherited a directory containing an incompatible version of the same header from your build system via the CPATH environment variable (effectively appending that directory to the -I list from the right).
gcc include clang
asked Nov 22 at 20:40
vega8
5071320
1
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36
add a comment |
Both gcc and clang seem to silently discard /usr/include from the list of include directories when explicitly included via -I.
Is there a specific reason as to why common compilers apparently don't allow to include the system's include dir?
background:
Suppose you depend on a header file located in /usr/include while having inherited a directory containing an incompatible version of the same header from your build system via the CPATH environment variable (effectively appending that directory to the -I list from the right).
gcc include clang
asked Nov 22 at 20:40
vega8
5071320
Both gcc and clang seem to silently discard /usr/include from the list of include directories when explicitly included via -I.
Is there a specific reason as to why common compilers apparently don't allow to include the system's include dir?
background:
Suppose you depend on a header file located in /usr/include while having inherited a directory containing an incompatible version of the same header from your build system via the CPATH environment variable (effectively appending that directory to the -I list from the right).
gcc include clang
gcc include clang
asked Nov 22 at 20:40
vega8
5071320
asked Nov 22 at 20:40
vega8
5071320
asked Nov 22 at 20:40
vega8
5071320
asked Nov 22 at 20:40
vega8
5071320
asked Nov 22 at 20:40
vega8
5071320
5071320
1
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36
add a comment |
1
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36
1
1
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36
add a comment |
1 Answer
1
active
oldest
votes
GCC ignores -I/usr/include because it is a system header directory by default, and using -I would turn it into non-system header, leading to confusing behavior, particularly with system headers that are not entirely aligned with language standards. (GCC gives system headers more latitude and suppresses warnings, for example.)
If you use -isystem /usr/include, then /usr/include moves to the front of the search list. However, you will likely have to move the other default search path entries as well, to avoid breaking too many things. gcc -v will print the entire search path.
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
But please don't use-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.
– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystemwouldn't be able to overrideCPATHanyway since it has lower precedence thanCPATH(which effectively is equivalent to-I).
– vega8
Nov 23 at 14:56
-nostdinccould help, though that's going to be a fragile hack.
– Marc Glisse
Nov 24 at 22:25
add a comment |
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1 Answer
1
active
oldest
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
GCC ignores -I/usr/include because it is a system header directory by default, and using -I would turn it into non-system header, leading to confusing behavior, particularly with system headers that are not entirely aligned with language standards. (GCC gives system headers more latitude and suppresses warnings, for example.)
If you use -isystem /usr/include, then /usr/include moves to the front of the search list. However, you will likely have to move the other default search path entries as well, to avoid breaking too many things. gcc -v will print the entire search path.
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
But please don't use-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.
– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystemwouldn't be able to overrideCPATHanyway since it has lower precedence thanCPATH(which effectively is equivalent to-I).
– vega8
Nov 23 at 14:56
-nostdinccould help, though that's going to be a fragile hack.
– Marc Glisse
Nov 24 at 22:25
add a comment |
GCC ignores -I/usr/include because it is a system header directory by default, and using -I would turn it into non-system header, leading to confusing behavior, particularly with system headers that are not entirely aligned with language standards. (GCC gives system headers more latitude and suppresses warnings, for example.)
If you use -isystem /usr/include, then /usr/include moves to the front of the search list. However, you will likely have to move the other default search path entries as well, to avoid breaking too many things. gcc -v will print the entire search path.
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
But please don't use-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.
– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystemwouldn't be able to overrideCPATHanyway since it has lower precedence thanCPATH(which effectively is equivalent to-I).
– vega8
Nov 23 at 14:56
-nostdinccould help, though that's going to be a fragile hack.
– Marc Glisse
Nov 24 at 22:25
add a comment |
GCC ignores -I/usr/include because it is a system header directory by default, and using -I would turn it into non-system header, leading to confusing behavior, particularly with system headers that are not entirely aligned with language standards. (GCC gives system headers more latitude and suppresses warnings, for example.)
If you use -isystem /usr/include, then /usr/include moves to the front of the search list. However, you will likely have to move the other default search path entries as well, to avoid breaking too many things. gcc -v will print the entire search path.
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
GCC ignores -I/usr/include because it is a system header directory by default, and using -I would turn it into non-system header, leading to confusing behavior, particularly with system headers that are not entirely aligned with language standards. (GCC gives system headers more latitude and suppresses warnings, for example.)
If you use -isystem /usr/include, then /usr/include moves to the front of the search list. However, you will likely have to move the other default search path entries as well, to avoid breaking too many things. gcc -v will print the entire search path.
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
edited Nov 22 at 21:39
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
answered Nov 22 at 20:55
Florian Weimer
14.5k2943
14.5k2943
But please don't use-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.
– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystemwouldn't be able to overrideCPATHanyway since it has lower precedence thanCPATH(which effectively is equivalent to-I).
– vega8
Nov 23 at 14:56
-nostdinccould help, though that's going to be a fragile hack.
– Marc Glisse
Nov 24 at 22:25
add a comment |
But please don't use-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.
– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystemwouldn't be able to overrideCPATHanyway since it has lower precedence thanCPATH(which effectively is equivalent to-I).
– vega8
Nov 23 at 14:56
-nostdinccould help, though that's going to be a fragile hack.
– Marc Glisse
Nov 24 at 22:25
But please don't use
-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.– Marc Glisse
Nov 22 at 21:34
But please don't use
-isystem /usr/include. The system headers are searched in a very specific order, and changing that order will break things.– Marc Glisse
Nov 22 at 21:34
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
Good point, it will likely be necessary to move the other default search paths as well.
– Florian Weimer
Nov 22 at 21:38
-isystem wouldn't be able to override CPATH anyway since it has lower precedence than CPATH (which effectively is equivalent to -I).– vega8
Nov 23 at 14:56
-isystem wouldn't be able to override CPATH anyway since it has lower precedence than CPATH (which effectively is equivalent to -I).– vega8
Nov 23 at 14:56
-nostdinc could help, though that's going to be a fragile hack.– Marc Glisse
Nov 24 at 22:25
-nostdinc could help, though that's going to be a fragile hack.– Marc Glisse
Nov 24 at 22:25
add a comment |
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1
Create a new directory, symlink the files you want there, and point -I at that new directory. This avoids side effects that you do not control.
– Marc Glisse
Nov 22 at 21:36