The ARM compilers have the ANSI C library headers built into a special, textually compressed, in-memory file system. By default, the C header files are used from this file system. The in-memory file system can be specified explicitly on the command line as -j- and -I-.

In addition, the C++ header files that are equivalent to the C library header files are also stored in the in-memory file system. The Rogue Wave library header files, and the ARM-supplied headers such as iostream.h are not stored in the in-memory file system.

Enclosing a #include filename in angle brackets indicates that the included file is a system file and ensures that the compiler looks first in its built-in file system. For example:

#include <stdio.h>

Enclosing a #include filename in double quotes indicates that it is not a system file. For example:

#include "myfile.h"

In this example, the compiler looks for the specified file in the appropriate search path. Refer to Specifying search paths for detailed information on how the ARM compilers search for include files.

By default, the ARM compilers adopt the search rules used by Berkeley UNIX systems. Under these rules, source files and #include header files are searched for relative to the current place. The current place is the directory containing the source or header file currently being processed by the compiler.

When a file is found relative to an element of the search path, the name of the directory containing that file becomes the new current place. When the compiler has finished processing that file, it restores the previous current place. At each instant, there is a stack of current places corresponding to the stack of nested #include directives.

For example, if the current place is ~/arm250/include and the compiler is seeking the include file sys/defs.h, it will locate ~/arm250/include/sys/defs.h if it exists.

When the compiler begins to process defs.h, the current place becomes ~/arm250/include/sys. Any file included by defs.h that is not specified with an absolute pathname is sought relative to ~/arm250/include/sys.

You can disable the stacking of current places with the compiler option -fk. This option makes the compiler use the search rule originally described by Kernighan and Ritchie in The C Programming Language. Under this rule, each non-rooted user #include is sought relative to the directory containing the source file that is being compiled.

You can set the ARMINC environment variable to specify a list of directories to be searched for included header and source files. Directories listed here will be searched immediately after any directories specified by the -I option on the command line. If the -j option is used, ARMINC is ignored.

Table 2.1 shows how the various command-line options affect the search path used by the compiler for included header and source files. The search path is different for double quoted include files and angle bracketed include files. The following conventions are used in the table: