The creation of PCH precompiled files for iOS development

This article turns from

Http://www.cnblogs.com/496668219long/p/4568265.html

Before Xcode6, create a new project Xcode automatically creates a "project name-prefix.pch" file under the supporting Files folder, which is also a header file, and the contents of the PCH header file can be shared and accessed by all other source files in the project. is a precompiled file.

First, let's talk about the role of PCH:

1. Store some global macros (macros that are used throughout the project)

2. Used to include all header files (header files that are used throughout the project)

3. Can automatically turn on or off the log output function

Although it took a long time to Xcode6 but the project was created before XCODE5, the PCH file was not found to be missing from the beginning. Why should Apple do this, perhaps because people put a lot of header files and macro definitions into the PCH, resulting in a long compilation time. Apple to get rid of him may be to speed up the compilation time to increase the user experience. Although the convenience of programming has been lost. Have to admire Apple's user-centric approach to thinking. A more detailed discussion can go up to StackOverflow and see http://stackoverflow.com/questions/24158648/. Why-isnt-projectname-prefix-pch-created-automatically-in-xcode-6.

How to add a PCH file in Xcode:

Command+n, open the new File window: ios->other->pch file, create a PCH

2, in the project targets inside building setting search Prefix header, and then the Precompile Prefix header to the right of no change to Yes:

3. Then double-click on the right side of the Prefix header below the precompile Prefix header to add the project path to the PCH file you just created, adding the format: "$ (srcroot)/project name/PCH filename", $ (srcroot) The meaning of the project root directory. If you're not sure, you can right-click the PCH file and show in Finder:

The yellow circle comes out of $ (srcroot), which is the project root directory, and then there is a Pchtext and PCH two folders, so the path to the complete PCH file is: $ (srcroot)/pchtext/pch

Once added, click Enter, and he will automatically help you to become the path of your project:

Yes, compile the program, if you have an error check the path you added is correct.

4, Precompile Prefix header is yes, pre-compiled PCH file will be cached, can improve the speed of compilation

5. Declare a macro definition in the prefixheader.pch file, for example: macro defines a color

You can then use it directly in other classes without introducing a header file, such as in Rootviewcontroller, which you can use directly when you need it.

6. If the following error occurs, the project path is introduced incorrectly

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