12.7.5 Standard Header Implementation

C has 17 standard headers (<stdio.h>, <string.h>, <stdlib.h>, and others). These headers are delivered as part of the Solaris operating system, in the directory /usr/include. C++ has those same headers, with the added requirement that the various declared names appear in both the global namespace and in namespace std. On versions of the Solaris operating system prior to version 8, the C++ compiler supplies its own versions of these headers instead of replacing those in the /usr/include directory.

C++ also has a second version of each of the C standard headers (<cstdio>, <cstring>, and <cstdlib>, and others) with the various declared names appearing only in namespace std. Finally, C++ adds 32 of its own standard headers (<string>, <utility>, <iostream>, and others).

The obvious implementation of the standard headers would use the name found in C++ source code as the name of a text file to be included. For example, the standard headers <string> (or <string.h>) would refer to a file named string (or string.h) in some directory. That obvious implementation has the following drawbacks:

• You cannot search for just header files or create a makefile rule for the header files if they do not have file name suffixes.

• If you have a directory or executable program named string, it might erroneously be found instead of the standard header file.

• On versions of the Solaris operating system prior to the Solaris 8 operating system, the default dependencies for makefiles when .KEEP_STATE is enabled can result in attempts to replace standard headers with an executable program. (A file without a suffix is assumed by default to be a program to be built.)

To solve these problems, the compiler include directory contains a file with the same name as the header, along with a symbolic link to it that has the unique suffix .SUNWCCh (SUNW is the prefix for all compiler-related packages, CC is the C++ compiler, and h is the usual suffix for header files). When you specify <string>, the compiler rewrites it to <string.SUNWCCh> and searches for that name. The suffixed name will be found only in the compiler’s own include directory. If the file so found is a symbolic link (which it normally is), the compiler dereferences the link exactly once and uses the result (string in this case) as the file name for error messages and debugger references. The compiler uses the suffixed name when emitting file dependency information.

The name rewriting occurs only for the two forms of the 17 standard C headers and the 32 standard C++ headers, only when they appear in angle brackets and without any path specified. If you use quotes instead of angle brackets, specify any path components, or specify some other header, no rewriting occurs.

The following table illustrates common situations.

If the compiler does not find header.SUNWCCh, the compiler restarts the search looking for the name as provided in the #include directive. For example, given the directive #include <string>, the compiler attempts to find a file named string.SUNWCCh. If that search fails, the compiler looks for a file named string.

12.7.5.1 Replacing Standard C++ Headers

Because of the search algorithm described in 12.7.5 Standard Header Implementation, you do not need to supply SUNWCCh versions of the replacement headers described in 12.7.3 Installing the Replacement Library. But you might run into some of the described problems. If so, the recommended solution is to add symbolic links having the suffix .SUNWCCh for each of the unsuffixed headers. That is, for file utility, you would run the command

example% ln -s utility utility.SUNWCCh

When the compiler looks first for utility.SUNWCCh, it will find it, and not be confused by any other file or directory called utility.

12.7.5.2 Replacing Standard C Headers

Replacing the standard C headers is not supported. If you nevertheless wish to provide your own versions of standard headers, the recommended procedure is as follows:

• Put all the replacement headers in one directory.

• Create a .SUNWCCh symbolic link to each of the replacement headers in that directory.

• Cause the directory that contains the replacement headers to be searched by using the -I directives on each invocation of the compiler.

For example, suppose you have replacements for <stdio.h> and <cstdio>. Put the files stdio.h and cstdio in directory /myproject/myhdr. In that directory, run these commands:

example% ln -s stdio.h stdio.h.SUNWCCh
example% ln -s cstdio cstdio.SUNWCCh

Use the option -I/myproject/mydir on every compilation.

Caveats:

• If you replace any C headers, you must replace them in pairs. For example, if you replace <time.h>, you should also replace <ctime>.

• Replacement headers must have the same effects as the versions being replaced. That is, the various runtime libraries such as libCrun, libC, libCstd, libc, and librwtool are built using the definitions in the standard headers. If your replacements do not match, your program is unlikely to work.