If you've ever looked under the hood at a Mac OS X application for controlling fans or reading sensor data, then you will undoubtedly have seen two files - smc.c and smc.h. Used in just about every project that relies upon reading SMC values.

The problem is, these files have become something of a dark magic - with no real comments or explanations anywhere, no bindings for NS* classes and a lack of any OOP implementation.

To combat that I've done the following;

• Wrapped the functionality up in to a convenient class
• Wrote some fairly extensive comments
• Included the ability to read values in to NSNumber and NSString objects.

If people do want this then I will add it in, at some point. Alternatively, fork this and give me a pull request!

Well, this is actually a lie - as this supports more data types than some of the older copies of smc.c that are still dotted around the internet. However, don't go expecting every possible SMC key to return a valid value. If you find a key that doesn't, please fill in an "Issue" here on Github and I'll have a look at it. (Or, once again, fork it!)

I haven't used Objective C since the days of the iPhone SDK (that's before the iPad came along and it was renamed the iOS SDK for you newcomers! ;)) - so I'm very much rusty!

SMCWrapper *smc = [SMCWrapper sharedWrapper];

NSNumber *CPUTemp;
[smc readKey:"TC0P" intoNumber:&CPUTemp];

NSString *fanRPM;
[smc readKey:"F0Ac" asString:&fanRPM]; 

int main(int argc, const char * argv[])
{
    SMCWrapper *smc = [SMCWrapper sharedWrapper];

    // TC0P => CPU Temperature
    NSNumber *temp;
    if ( [smc readKey:"TC0P" intoNumber:&temp] ){
        NSLog(@"CPU Temperature:\t %@C", [temp stringValue]);
    }
    
    // F0Ac => Fan0 Actual RPM
    NSNumber *fanRPM;
    if ( [smc readKey:"F0Ac" intoNumber:&fanRPM] ){
        NSLog(@"Fan #0 RPM:\t %@", [fanRPM stringValue]);
    }

    // F0Mn => Min RPM
    NSString *minRPM;
    if ( [smc readKey:"F0Mn" asString:&minRPM] ){
        NSLog(@"Fan #0 Min RPM:\t %@", minRPM);
    }

    // F0Mx => Max RPM
    NSString *maxRPM;
    if ( [smc readKey:"F0Mx" asString:&maxRPM] ){
        NSLog(@"Fan #0 Max RPM:\t %@", maxRPM);
    }
    
    return 0;
}

On my 13" Early 2004 MacBook Air, this currently produces..

2014-09-30 02:48:22.485 SMCInfo[56428:386055] CPU Temperature: 42.75C
2014-09-30 02:48:22.487 SMCInfo[56428:386055] Fan #0 RPM: 1203
2014-09-30 02:48:22.487 SMCInfo[56428:386055] Fan #0 Min RPM: 1200.00
2014-09-30 02:48:22.488 SMCInfo[56428:386055] Fan #0 Max RPM: 6500.00

I'm fairly certain that the original files were wrote by a guy named devnull, but released under the GNU General Public License all the same. As such, this class itself is also released under the GNU General Public License.

Special mentions are deserved for @HHoltmann - Hendrik Holtmann, for his smcFanControl repository which provided some good reading, @stny - Naoya SATO for his Thermo repository - which included an smc.c version which supported a good number of data types.