The FILENAME_H is a convention. If you really wanted, you could use #ifndef FLUFFY_KITTENS as a header guard (provided it was not defined anywhere else), but that would be a tricky bug if you defined it somewhere else, say as the number of kittens for something or other. In the header file add.h the declarations … Read more
The preprocessor is a program that takes your program, makes some changes (for example include files (#include), macro expansion (#define), and basically everything that starts with #) and gives the “clean” result to the compiler. The preprocessor works like this when it sees #include: When you write: #include “some_file” The contents of some_file almost literally … Read more
It depends on how much portable your program is expected to be. As long as you are writing a program which is supposed to work with compilers which you know definitely support #prama once, just using #pragma once should suffice. But doing so you restrict your program to set of compilers which support the implementation … Read more
The FILENAME_H is a convention. If you really wanted, you could use #ifndef FLUFFY_KITTENS as a header guard (provided it was not defined anywhere else), but that would be a tricky bug if you defined it somewhere else, say as the number of kittens for something or other. In the header file add.h the declarations … Read more
No, there’s no difference between the two when used that way. The latter form (using defined()) is useful when the initial #if or one of the subsequent #elif conditions needs a more complex test. #ifdef will still work, but it might be clearer using #if defined() in that case. For example, if it needs to … Read more
The preprocessor is a program that takes your program, makes some changes (for example include files (#include), macro expansion (#define), and basically everything that starts with #) and gives the “clean” result to the compiler. The preprocessor works like this when it sees #include: When you write: #include “some_file” The contents of some_file almost literally … Read more
A directive like #pragma once is not trivial to define in a fully portable way that has clear an unambiguous benefits. Some of the concepts for which it raises questions are not well defined on all systems that support C, and defining it in a simple way might provide no benefit over conventional include guards. … Read more
FIRST QUESTION: Why aren’t include guards protecting my header files from mutual, recursive inclusion? They are. What they are not helping with is dependencies between the definitions of data structures in mutually-including headers. To see what this means, let’s start with a basic scenario and see why include guards do help with mutual inclusions. Suppose … Read more
Add this to the page that you want to only be included <?php if(!defined(‘MyConst’)) { die(‘Direct access not permitted’); } ?> then on the pages that include it add <?php define(‘MyConst’, TRUE); ?>
foo.h #ifndef FOO_H_ /* Include guard */ #define FOO_H_ int foo(int x); /* An example function declaration */ #endif // FOO_H_ foo.c #include “foo.h” /* Include the header (not strictly necessary here) */ int foo(int x) /* Function definition */ { return x + 5; } main.c #include <stdio.h> #include “foo.h” /* Include the header … Read more