The PCH file for iOS learning

1. pch File overview

• PCH file is a precompiled header file (a generic extension of. PCH) is a project in which the more stable code is pre-compiled and placed in a file (. PCH). These pre-compiled code can be any C/s code--or even an inline function--that is more stable throughout the project, i.e. code that is not often modified during engineering development.

• In the previous version of Xcode6.0, the PCH file was automatically present in the generated single View application project, and the PCH was removed afterXcode6.0 , which accelerated the compilation speed for some trivial header file references!

• Works for the XCODE5:

2. pch File Creation (Previous versions of Xcode6.0）

In Project Command + n-> in iOS other-> PCH file-> next-> Create

PCH files are compiled in advance, so we're going to tell the project. Specific operations such as:

Of course, if you want to fill in, you can use $ (srcroot) to get the path of your project file, complete can be written as:$ (srcroot)/pchtest/header.pch

3. The role of PCH files

• Store some of the common macros

• Store some common header files , general development of the Chinese tool class header files or classification header files.

• Managing log Output

custom log: #define ZFLOG (...) NSLog (__va__args__)

Variable parameters inside the macro:...

Variable parameters in the function :__va__args__

　　Log output is very performance-intensive, generally released when the log file is not required, only when debugging.

We have two simple ways to eliminate all log output in the project when it comes to the launch.

① we can comment directly behind #define ZFLOG (...) //NSLog (__va__args__)

②   You can also conditionally compile with a macro, and in the debugging phase, Xcode automatically defines a debug macro , using this macro, you can make conditional compilation.

#ifdef // Commissioning Phase #define Zflog (...) NSLog (__va__args__) #else//  release phase #define zflog (...) #endif

4. pch File Usage considerationsInPchwritten about OC , preferably in #ifdef __objc__ ,Xcode defines this macro in each OC file, which means that only oc Files in the file to have these macros, to avoid the project has a C file when the error. such as inCfile, use the#import,you will get an error, becauseCFile not recognized#import, onlyOC file to be recognized. In pch c file share #import error.

#ifdef // the correct notation    for OC files #import <UIKit/UIKit.h>    #import <Foundation/Foundation.h>#endif# Import"ZFTool.h"//  write here may error, so do not write here

The PCH file for iOS learning