#import using angle brackets < > and quote mark

Question

I'm wondering what decides whether you're allowed to use <Header.h> or "Header.h" when you're importing files in Objective-C. So far my observation has been that you use the quote marks "" for files in your project that you've got the implementation source to, and angle brackets <> when you're referencing a library or framework.

But how exactly does that work? What would I have to do to get my own classes to use the brackets? Right now Xcode will not allow me to do that for my own headers.

Also, by looking in some frameworks headers, I see that the headers reference each other with <frameworkname/file.h>. How does that work? It looks a lot like packages in Java, but as far as I know, there is no such thing as a package in Objective-C.

Answer 1

Objective-C has this in common with C/C++; the quoted form is for "local" includes of files (you need to specify the relative path from the current file, e.g. #include "headers/my_header.h"), while the angle-bracket form is for "global" includes -- those found somewhere on the include path passed to the compiler (e.g. #include <math.h>).

So to have your own headers use < > not " " you need to pass either the relative or the absolute path for your header directory to the compiler. See "How to add a global include path for Xcode" for info on how to do that in Xcode.

See this MSDN page for more info.

Answer 2

WHAT IS HEADER FILE ? Header files contain definitions of functions and variables which can be incorporated into any C program by using the pre-processor #include statement. Standard header files are provided with each compiler, and cover a range of areas, string handling, mathematical, data conversion, printing and reading of variables. Ex- #include it contain the information about input like scanf(),and out put like printf() function and etc in a compiler.

INCLUDE

1) #INCLUDE:- It is a pre-processor that process before process of main function. The main work of pre-processor is to initialize the environment of program i.e that is the program with the header file. 2).h:- (Header file) A header file is a file with extension .h which contains C function declarations and macro definitions and to be shared between several source files. Q) There are two types of header files: the files that the programmer writes and the files that come with your compiler ? A)In a angular brackets Angular-bracket form is for "global" includes -- those found somewhere on the include path passed to the compiler (e.g. #include) It is used for using of library function which is all ready define in compiler. In C the convention is that header files in <> bracket are searched in 'system' directories  B) Quote marks:- “header.h” quoted form is for "local" includes of files (you need to specify the relative path from the current file, e.g. #include "headers/my_header.h") In C the convention is that header files in " " are searched in user or local directories. In it one file to be included in another .(FILE INCLUSION). It can be used in two cases: Case 1: If we have a very large program, the code is best divided int several different files,each containing a set of related functions. Case 2: There are some functions and micros definitions that we need at most in all programs that we write. Ex

Answer 3

In C the convention is that header files in <> bracket are searched in 'system' directories and "" in user or local directories.

The definition of system and local is a bit vague I guess. I believe it looks in system directories in include path or in CPPFLAGS for and local directory or directory specified with -I to compiler are searched for "header.h" files.

I assume it works similarly for Objective-C.

Answer 4

Just stumbled upon the same problem, there are 2 types of search paths is Xcode:

User Header Search Paths
Header Search Paths

If you add your own include folders into Header Search Paths, you can use angled brackets without any problem.

Answer 5

To import your own classes using "< >" you have to put the header files (*.h) in the lib folder of compiler or set a SYSTEM VARIABLES ponting to your lib folder.

Answer 6

Or set Always Search User Path to YES so you can use angle brackets.