Question

I’m working on a Objective-C program where I’m getting bitfields over the network, and need to set boolean variables based on those bits.

Currently I’m representing the bitfields as int‘s, and then using bit shifting, similar to this (all the self properties are BOOL):

typedef enum {
    deleteFlagIndex = 0,
    uploadFlagIndex = 1,
    moveFlagIndex = 2,
    renameFlagIndex = 3
} PrivilegeFlagIndex;

int userFlag = 5; //for example

// this would be YES
self.delete = ((userFlag & (1 << deleteFlagIndex)) == (1 << deleteFlagIndex));
// this would be NO
self.upload = ((userFlag & (1 << uploadFlagIndex)) == (1 << uploadFlagIndex));

And this works (to the best of my knowledge) but I’m wondering – is there a more efficient concise way to code all the bit twiddling using a fancy trick/hack? I ask because I’ll be doing this for a lot of flags (more than 30).

I did realize I could use this method this as well:

self.move = ((userFlag & (1 << moveFlagIndex)) > 0)

…which does reduce the amount of typing, but I don’t know if there’s a good reason to not do it that way.

Edit: Revised to say concise rather than efficient – I wasn’t worried about execution performance, but rather tips and best practices for doing this in a smart way.

Answer 1

Try:

typedef enum {
    deleteFlag = 1 << 0,
    uploadFlag = 1 << 1,
    moveFlag = 1 << 2,
    renameFlag = 1 << 3
} PrivilegeFlags;

Now you can combine them using | directly.

Usually, it suffices to check against 0:

if (userFlag & deleteFlag) {
    // delete...
}