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| -rw-r--r-- | hurd/porting/guidelines.mdwn | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/hurd/porting/guidelines.mdwn b/hurd/porting/guidelines.mdwn index bcfc8dd5..8dd27a52 100644 --- a/hurd/porting/guidelines.mdwn +++ b/hurd/porting/guidelines.mdwn @@ -232,3 +232,40 @@ Not implemented, not POSIX. Try to disable the feature in the package. ## <a name="parport"> <linux/parport.h> <linux/ppdev.h> </a> There is no programming interface for the parallel port on GNU/Hurd yet. + +## <a name="errno"> `errno` values </a> + +When dealing with `errno`, you should always use the predefined error codes defined with the `E*` constants, instead of manually comparing/assigning/etc with their values. + +For example (C/C++): + + /* check whether it does not exist */ + if (errno == 2) + ... + +or Python: + + # check whether it does not exist + try: + ... + except OSError, err: + err.errno == 2: + ... + +This is wrong, as [the actual values of the `E*` are unspecified (per POSIX)](http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_03.html#tag_02_03). You must always use the predefined constants for the possible errors. + +For example (C/C++): + + /* check whether it does not exist */ + if (errno == ENOENT) + ... + +With Python, you can use the [`errno` module](http://docs.python.org/library/errno.html) for the various constants: + + # check whether it does not exist + try: + ... + except OSError, err: + import errno + err.errno == errno.ENOENT: + ... |