转自 http://stackoverflow.com/questions/25951195/swift-print-vs-println-vs-nslog#

1. printlnvsprint:

   Prior to Swift 2,printlnwould add a newline at the end of the results,whereasprintwould not.

   Starting in Swift 2,241)">printlnis no longer used. One would generally useprint(either withoutappendNewlineparameter,or having that parameter set totrue) to print a line followed with a newline character. You would useprintwithappendNewlineoffalseif you want to print a string without a newline at the end.

2. NSLogvsprint/println:

   • NSLogis slower;

   • NSLogadds a timestamp and identifier to the output,241)">printlnwill not;

   • NSLogsynchronizes the log statements so that if you're issuing logs from different threads concurrently,they won't overlap with each other;printlncan result in jumbled output if performed simultaneously from separate threads without doing some synchronization (e.g. dispatching it to some serial queue,such as the main queue);

   • When performed on physical device,241)">NSLogstatements appear in the device's console whereasprintlnonly appears in the debugger console.

Generally in Swift,you'd useprintln,though you can useNSLog,when needed (e.g.,it's critical that it appears in the console or if you're doing this from multiple threads and you don't want to have to synchronize this yourself). Either of these should be able to display your dictionary without incident.

you can pass in an NSString to println,but not NSLog; you can add args for NSLog,but not println; Swift style string interpolation sometimes crashes for NSLog,but not println.