UNIX for Dummies Questions & Answers

Hi I was wondering if it would be possible to get the full octal permissions of a file by using something in the stat() system call. Can this be done without going through all of the seperate permissions (e.g. read for user, write for user .... etc.)? also how can this octal permission be changed to accomadate new permissions? (can i simply store the octal permission and then perform normal computations on it according to the permission im adding or taking away? Thanks in advance for anyone who could explain this.

You don't have to "go through" them individually. stat() returns them all at once. They're all different bits of one binary integer.

You change them with chmod(). So you'd get the bits you want with stat(), alter them, then chmod() it to the new one.

To add bits, | them.

Code:

// Add read and write permissions.
// This is harmless if they're already set.
int new_perms=old_perms | 0006;

To remove bits, & their opposite. ~ is the bitwise opposite, so:

Code:

// Remove read and write permissions.  This is harmless
// if they're already missing.
int new_perms=old_perms & ~0006;

so i could do something like int old_perms = stat() to set the old perms is what your saying and simply perform the operations you specified?or do i need to use st_mode and further??sorry if im kinda slow when it comes to this stuff.

No, stat() doesn't return them in that way. It reads into an entire structure with various members, only one of which contains file permissions. See man 2 stat for details.

ok i figured it all out thanks alot i really appreciate your help

---------- Post updated at 07:01 PM ---------- Previous update was at 06:14 PM ----------

Hi the newPerm = oldPerm | ####; is working in my code but for some reason each case of newPerm = oldPerm & ~####; is returning an error that reads "parameter names without types in function declaration, i think when this is being called...
chmod(file, newPerm); what could be the problem?

Without seeing your code I couldn't say. Please post it.