DEBUG时的一些小技巧（随便写写）

Technical Q&A QA1669

Improved logging in Objective-C

Q:  How can I add context information - such as the current method or line number - to my logging statements?

A: The C preprocessor provides a number of standard macros that give you information about the current file, line number, or function. Additionally, Objective-C has the _cmd implicit argument which gives the selector of the current method, and functions for converting selectors and classes to strings. You can use these in your NSLog statements to provide useful context during debugging or error handling. 

Listing 1  Example of logging the current method and line number. Paste it into your project, and see what it prints!

NSMutableArray *someObject = [NSMutableArray array];

NSLog(@"%s:%d someObject=%@", __func__, __LINE__, someObject);

[someObject addObject:@"foo"];

NSLog(@"%s:%d someObject=%@", __func__, __LINE__, someObject);

The following tables list the most popular macros and expressions which might be useful in your logging statements.

Table 1  Preprocessor macros and for logging in C/C++/Objective-C.

Macro	Format Specifier	Description
__func__	%s	Current function signature.
__LINE__	%d	Current line number in the source code file.
__FILE__	%s	Full path to the source code file.
__PRETTY_FUNCTION__	%s	Like __func__, but includes verbose type information in C++ code.

Table 2  Expressions for logging in Objective-C.

Expression	Format Specifier	Description
NSStringFromSelector(_cmd)	%@	Name of the current selector.
NSStringFromClass([self class])	%@	Name of the current object's class.
[[NSString stringWithUTF8String:__FILE__] lastPathComponent]	%@	Name of the source code file.
[NSThread callStackSymbols]	%@	NSArray of the current stack trace as programmer-readable strings. For debugging only, do not present it to end users or use to do any logic in your program.

原样的吧官方API文档介绍拷了过来，我们可以看到上面有C的方法名、行号、文件名的输出

我们在DEBugLog的时候，可以输出一些信息，帮助我们监控程序的执行，出错的时候也可以尽快的发现问题所在。

NSLog在输出C的字符串的时候，不能输出汉字，如果有汉字的话我们可以使用printf进行打印