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After you have invoked configure, you will discover a number of generated files in your build tree. The build directory structure created by configure and the number of files will vary from package to package. Each of the generated files are described below and their relationships are shown in the chapter called Generated File Dependencies:
configure can cache the results of system tests that have been performed to speed up subsequent tests. This file contains the cache data and is a plain text file that can be hand-modified or removed if desired.
As configure runs, it outputs a message describing each test it performs and the result of each test. There is substantially more output produced by the shell and utilities that configure invokes, but it is hidden from the user to keep the output understandable. The output is instead redirected to config.log. This file is the first place to look when configure goes hay-wire or a test produces a nonsense result. A common scenario is that configure, when run on a Solaris system, will tell you that it was unable to find a working C compiler. An examination of config.log will show that Solaris' default /usr/ucb/cc is a program that informs the user that the optional C compiler is not installed.
configure generates a shell script called config.status that may be used to recreate the current configuration. That is, all generated files will be regenerated. This script can also be used to re-run configure if the --recheck option is given.
Many packages that use configure are written in C or C++. Some of the tests that configure runs involve examining variability in the C and C++ programming languages and implementations thereof. So that source code can programmatically deal with these differences, #define preprocessor directives can be optionally placed in a config header, usually called config.h, as configure runs. Source files may then include the config.h file and act accordingly:
#if HAVE_CONFIG_H
# include <config.h>
#endif /* HAVE_CONFIG_H */
#if HAVE_UNISTD_H
# include <unistd.h>
#endif /* HAVE_UNISTD_H */ |
We recommend always using a config header.
One of the common functions of configure is to generate Makefiles and other files. As it has been stressed, a Makefile is just a file often generated by configure from a corresponding input file (usually called Makefile.in). The following section will describe how you can use make to process this Makefile. There are other cases where generating files in this way can be helpful. For instance, a Java developer might wish to make use of a defs.java file generated from defs.java.in.
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