Objectice-C log information

NSLog is used in Objectice-C to output log information. The biggest difference between Objectice-C and C is that "fox" and @ "fox ", a c string is a pointer to a byte string, and an NSString (starting with @) is an object. The method for operating the C string is to modify the value saved in each byte. NSString strings are unchangeable. You cannot access each byte and edit them. In addition, the actual string data is not stored in the object.

NSString * fox = @ "fox ";
Printf ("Hello: % s \ n", [fox UTF8String]);
NSLog ("Hello: % @", fox); // introduce the object descriptor % @ in NSLog for output objects.

Common string formats:

% @ Object

% "%" Text character
% D, % I integer
% U unsigned integer
% F floating point/double-Character
% X, % X binary integer
% O octal integer
% Zu size_t
% P pointer
% E floating point/double-character (Scientific Computing)
% G floating point/double-Character
% S C string
%. * S Pascal string
% C characters
% C unichar
% Lld 64-bit long integer (long)
% Llu unsigned 64-bit long integer
% Lf 64-bit dual-Character

Another useful logging function is CFShow (). It uses an object as a parameter to output the snapshot description of the object to stderr.

CFShow (fox );