Logging Messages

You use the NSLog and NSLogv functions to log error and informational messages. These messages are written to stderr.

The message consists of a timestamp and the process ID prefixed to the string you pass in. You compose this string with a format string and one or more arguments to be inserted into the string. The format specification allowed by these functions is that which is understood by NSString’s formatting capabilities (which is not necessarily the set of format escapes and flags understood by printf). For example, the following code fragment, outputs a string constructed from NSString and int arguments.

int recNum;

NSString *recName;

/* ... */

NSLog( @"Record %d is %@", recNum, recName );

See Formatting String Objects for a description of the various format specifiers.

In general, you should use the NSLog function instead of calling NSLogv directly. If you do call NSLogv directly, you must have prepared the required variable argument list by calling the standard C macro va_start. Upon completion, you must similarly call the standard C macro va_end for this list.