You should define these macros by using `#define' preprocessor
directives at the top of your source code files. These directives
-*must* come before any `#include' of a system header file. It is best
+_must_ come before any `#include' of a system header file. It is best
to make them the very first thing in the file, preceded only by
comments. You could also use the `-D' option to GCC, but it's better
if you make the source files indicate their own meaning in a
self-contained way.
+ This system exists to allow the library to conform to multiple
+standards. Although the different standards are often described as
+supersets of each other, they are usually incompatible because larger
+standards require functions with names that smaller ones reserve to the
+user program. This is not mere pedantry -- it has been a problem in
+practice. For instance, some non-GNU programs define functions named
+`getline' that have nothing to do with this library's `getline'. They
+would not be compilable if all features were enabled indiscriminately.
+
+ This should not be used to verify that a program conforms to a
+limited standard. It is insufficient for this purpose, as it will not
+protect you from including header files outside the standard, or
+relying on semantics undefined within the standard.
+
- Macro: _POSIX_SOURCE
If you define this macro, then the functionality from the POSIX.1
standard (IEEE Standard 1003.1) is available, as well as all of the
ISO C facilities.
+ The state of `_POSIX_SOURCE' is irrelevant if you define the macro
+ `_POSIX_C_SOURCE' to a positive integer.
+
- Macro: _POSIX_C_SOURCE
- If you define this macro with a value of `1', then the
- functionality from the POSIX.1 standard (IEEE Standard 1003.1) is
- made available. If you define this macro with a value of `2',
- then both the functionality from the POSIX.1 standard and the
- functionality from the POSIX.2 standard (IEEE Standard 1003.2) are
- made available. This is in addition to the ISO C facilities.
+ Define this macro to a positive integer to control which POSIX
+ functionality is made available. The greater the value of this
+ macro, the more functionality is made available.
+
+ If you define this macro to a value greater than or equal to `1',
+ then the functionality from the 1990 edition of the POSIX.1
+ standard (IEEE Standard 1003.1-1990) is made available.
+
+ If you define this macro to a value greater than or equal to `2',
+ then the functionality from the 1992 edition of the POSIX.2
+ standard (IEEE Standard 1003.2-1992) is made available.
+
+ If you define this macro to a value greater than or equal to
+ `199309L', then the functionality from the 1993 edition of the
+ POSIX.1b standard (IEEE Standard 1003.1b-1993) is made available.
+
+ Greater values for `_POSIX_C_SOURCE' will enable future extensions.
+ The POSIX standards process will define these values as necessary,
+ and the GNU C Library should support them some time after they
+ become standardized. The 1996 edition of POSIX.1 (ISO/IEC 9945-1:
+ 1996) states that if you define `_POSIX_C_SOURCE' to a value
+ greater than or equal to `199506L', then the functionality from
+ the 1996 edition is made available.
+
+ The Single Unix Specification specify that setting this macro to
+ the value `199506L' selects all the values specified by the POSIX
+ standards plus those of the Single Unix Specification, i.e., is the
+ same as if `_XOPEN_SOURCE' is set to `500' (see below).
- Macro: _BSD_SOURCE
If you define this macro, functionality derived from 4.3 BSD Unix
If the macro `_XOPEN_SOURCE' has the value 500 this includes all
functionality described so far plus some new definitions from the
- Single Unix specification, version 2.
+ Single Unix Specification, version 2.
- Macro: _LARGEFILE_SOURCE
If this macro is defined some extra functions are available which
rectify a few shortcomings in all previous standards. More
- concreten the functions `fseeko' and `ftello' are available.
+ concrete the functions `fseeko' and `ftello' are available.
Without these functions the difference between the ISO C interface
(`fseek', `ftell') and the low-level POSIX interface (`lseek')
would lead to problems.
This macro was introduced as part of the Large File Support
extension (LFS).
- - Variable: Macro _LARGEFILE64_SOURCE
- If you define this macro an additional set of function gets
- available which enables to use on 32 bit systems to use files of
- sizes beyond the usual limit of 2GB. This interface is not
- available if the system does not support files that large. On
- systems where the natural file size limit is greater than 2GB
- (i.e., on 64 bit systems) the new functions are identical to the
- replaced functions.
+ - Macro: _LARGEFILE64_SOURCE
+ If you define this macro an additional set of function is made
+ available which enables 32 bit systems to use files of sizes beyond
+ the usual limit of 2GB. This interface is not available if the
+ system does not support files that large. On systems where the
+ natural file size limit is greater than 2GB (i.e., on 64 bit
+ systems) the new functions are identical to the replaced functions.
The new functionality is made available by a new set of types and
- functions which replace existing. The names of these new objects
- contain `64' to indicate the intention, e.g., `off_t' vs.
+ functions which replace the existing ones. The names of these new
+ objects contain `64' to indicate the intention, e.g., `off_t' vs.
`off64_t' and `fseeko' vs. `fseeko64'.
This macro was introduced as part of the Large File Support
extension (LFS). It is a transition interface for the time 64 bit
offsets are not generally used (see `_FILE_OFFSET_BITS'.
- - Variable: _FILE_OFFSET_BITS
- This macro lets decide which file system interface shall be used,
+ - Macro: _FILE_OFFSET_BITS
+ This macro determines which file system interface shall be used,
one replacing the other. While `_LARGEFILE64_SOURCE' makes the
64 bit interface available as an additional interface
- `_FILE_OFFSET_BITS' allows to use the 64 bit interface to replace
- the old interface.
+ `_FILE_OFFSET_BITS' allows the 64 bit interface to replace the old
+ interface.
- If `_FILE_OFFSET_BITS' is undefined or if it is defined to the
- value `32' nothing changes. The 32 bit interface is used and
+ If `_FILE_OFFSET_BITS' is undefined, or if it is defined to the
+ value `32', nothing changes. The 32 bit interface is used and
types like `off_t' have a size of 32 bits on 32 bit systems.
- If the macro is defined to the value `64' the large file interface
+ If the macro is defined to the value `64', the large file interface
replaces the old interface. I.e., the functions are not made
available under different names as `_LARGEFILE64_SOURCE' does.
Instead the old function names now reference the new functions,
This macro was introduced as part of the Large File Support
extension (LFS).
+ - Macro: _ISOC99_SOURCE
+ Until the revised ISO C standard is widely adopted the new features
+ are not automatically enabled. The GNU libc nevertheless has a
+ complete implementation of the new standard and to enable the new
+ features the macro `_ISOC99_SOURCE' should be defined.
+
- Macro: _GNU_SOURCE
- If you define this macro, everything is included: ISO C, POSIX.1,
- POSIX.2, BSD, SVID, X/Open, LFS, and GNU extensions. In the cases
- where POSIX.1 conflicts with BSD, the POSIX definitions take
- precedence.
+ If you define this macro, everything is included: ISO C89,
+ ISO C99, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU
+ extensions. In the cases where POSIX.1 conflicts with BSD, the
+ POSIX definitions take precedence.
If you want to get the full effect of `_GNU_SOURCE' but make the
BSD definitions take precedence over the POSIX definitions, use
If you define one of these macros, reentrant versions of several
functions get declared. Some of the functions are specified in
POSIX.1c but many others are only available on a few other systems
- or are unique to GNU libc. The problem is that the
- standardization of the thread safe C library interface still is
- behind.
+ or are unique to GNU libc. The problem is the delay in the
+ standardization of the thread safe C library interface.
- Unlike on some other systems no special version of the C library
+ Unlike on some other systems, no special version of the C library
must be used for linking. There is only one version but while
compiling this it must have been specified to compile as thread
safe.
git.samba.org / jlayton / glibc.git / blobdiff