Improved logging in Objective-C …

最新推荐文章于 2021-03-12 06:06:18 发布

shjborage

最新推荐文章于 2021-03-12 06:06:18 发布

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本文介绍了如何在Objective-C中通过使用预处理器宏和Objective-C特有的隐含参数来添加日志中的上下文信息，如当前方法名和行号。详细解释了如何在`NSLog`语句中利用这些信息进行调试或错误处理，提供了实用的示例代码。

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.

Document Revision History

Date	Notes
2011-10-04	Expanded logging examples.
2009-10-27	New document that describes use of preprocessor macros and Objective-C language features to provide better context in log statements.