IOS development-log printing (common)

IOS development-log printing (common)

Q: How do I print the current function and row number?

A: Some pre-compiled macros can be used as printing parameters to print the current function and row number. For example:

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

NSLog (@ "% s: % d obj = % @", _ func __, _ LINE __, self); // output style: // 17:13:17. 852 justTest [15079: 613] //-[ViewController viewDidLoad]: 38 obj =
 

Both func and line are pre-compiled macros, which are replaced with the current function and the current row number respectively during compilation. The following are some macros that are commonly used to print logs.

Macro	Description
_ Func __	Print the current function or method, c string
_ LINE __	Print the current row number, an integer
_ FILE __	Print the current file path, c string
_ PRETTY_FUNCTION __	Print the current function or method (including the parameter type in C ++), c string

Q: How do I print a class name, message name, and current stack information?

A: You can use the following methods to dynamically obtain the information at runtime.

Code	Description
NSStringFromSelector (SEL)	Obtain the selector name
NSStringFromSelector (_ cmd)	Get the current method name
NSStringFromClass ([object class])	Obtains the class name of an object.
[NSThread callStackSymbols]	Gets the stack of the current thread, which is an NSArry that contains all function names in the stack.

Q: How to print logs to a file?

A: You can use the freopen function to redirect standard output and standard error files. Because the printf function prints to the standard output (stdout), and The NSLog function prints to the standard error (stderr. Redirecting stdout and stderr to a file will make them print logs to a file.

freopen("/tmp/log.txt", "a+", stdout);freopen("/tmp/log.txt", "a+", stderr);