using lstat st_mode flags and masks

smoking81 · 10-03-2008, 01:11 AM

hello everybody!
i am a bit confused about the way the flags and masks defined for st_mode have to be used..
Suppose that I lstat-ed a file and want to retrieve first is permission in numeric format (eg 755) and then simply check if the owner has execute permission..
In the second simplier case, I shall write something like:

Code:

if( (statbuff.st_mode & S_IRWXU) && S_IXUSR )

or would something like

Code:

if (statbuff.st_mode && S_IXUSR)

suffice?

in the second case,isn't there a faster way to get the numbers 7 5 5 than making all the comparisons possible?

thanks! Bye

dmail · 10-03-2008, 05:17 AM

Code:

if( (statbuff.st_mode & S_IRWXU) && S_IXUSR )

You are mixing the logical and bitwise operators here. Checking that the user has read permissions is correct but then you use a logical and with S_IXUSR as this is none zero then it will always be true.

Code:

if (statbuff.st_mode && S_IXUSR)

Again here you have mixed your operators up.

Check for read and execute access
if( statbuff.st_mode & S_IRWXU && statbuff.st_mode & S_IXUSR )