C header files ifndef

It helps the linker a lot. This decreases build time and risk of facing multiple inclusion related errors. So the linker knows about the include files? James Kanze. It depends. You need some sort of include guard, but such a simple naming convention runs a great risk of name collision, e. I've deleted the code which generates the copyright, but of course, that will normally be inserted automatically as well. I'm not familiar with eclipse, but I would imagine that you can configure its editor to generate something along these lines as well.

The above is part of a Unix shell script, which I've configured my editor to execute whenever it opens a. This discussion thread is closed Start new discussion. How do header files work? Help with header files. We include the header file so that the compiler pulls in the declaration. After the compiler finishes compiling each. Typically, header files have an include guard or a pragma once directive to ensure that they are not inserted multiple times into a single.

Because a header file might potentially be included by multiple files, it cannot contain definitions that might produce multiple definitions of the same name. The following are not allowed, or are considered very bad practice:. Use of the using directive will not necessarily cause an error, but can potentially cause a problem because it brings the namespace into scope in every. The following example shows the various kinds of declarations and definitions that are allowed in a header file:.

Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. The preprocessor will skip over the entire contents of the file, and the compiler will not see it twice. Sometimes it is necessary to select one of the several different header files to be included into your program.

For instance, they might specify configuration parameters to be used on different sorts of operating systems. But as it grows, it becomes tedious, instead the preprocessor offers the ability to use a macro for the header name. This is called a computed include. C - Header Files Advertisements. Previous Page. Next Page.