Every file that a sourcefile includes, directly or indirectly, is what makedepend calls a dependency. These dependencies are then written to a makefile in such a way that make(1) will know which object files must be recompiled when a dependency has changed.
By default, makedepend places its output in the file named makefile if it exists, otherwise Makefile. An alternate makefile may be specified with the -f option. It first searches the makefile for the line
# DO NOT DELETE THIS LINE -- make depend depends on it.
or one provided with the -s option, as a delimiter for the dependency output. If it finds it, it will delete everything following this to the end of the makefile and put the output after this line. If it doesnt find it, the program will append the string to the end of the makefile and place the output following that. For each sourcefile appearing on the command line, makedepend puts lines in the makefile of the form
sourcefile.o: dfile ...
Where sourcefile.o is the name from the command line with its suffix replaced with .o, and dfile is a dependency discovered in a #include directive while parsing sourcefile or one of the files it included.
SRCS = file1.c file2.c ... CFLAGS = -O -DHACK -I../foobar -xyz depend: makedepend -- $(CFLAGS) -- $(SRCS)
|-Dname=def or -Dname|
|Define. This places a definition for name in makedepends symbol table. Without =def the symbol becomes defined as 1.|
|Include directory. This option tells makedepend to prepend includedir to its list of directories to search when it encounters a #include directive. By default, makedepend only searches the standard include directories (usually /usr/include and possibly a compiler-dependent directory).|
|Replace all of the standard include directories with the single specified include directory; you can omit the includedir to simply prevent searching the standard include directories.|
|-a||Append the dependencies to the end of the file instead of replacing them.|
|Filename. This allows you to specify an alternate makefile in which makedepend can place its output. Specifying - as the file name (i.e., -f-) sends the output to standard output instead of modifying an existing file.|
|Process file as input, and include all the resulting output before processing the regular input file. This has the same affect as if the specified file is an include statement that appears before the very first line of the regular input file.|
|Object file suffix. Some systems may have object files whose suffix is something other than .o. This option allows you to specify another suffix, such as .b with -o.b or :obj with -o:obj and so forth.|
|Object file prefix. The prefix is prepended to the name of the object file. This is usually used to designate a different directory for the object file. The default is the empty string.|
|Starting string delimiter. This option permits you to specify a different string for makedepend to look for in the makefile.|
|-wwidth||Line width. Normally, makedepend will ensure that every output line that it writes will be no wider than 78 characters for the sake of readability. This option enables you to change this width.|
|-v||Verbose operation. This option causes makedepend to emit the list of files included by each input file.|
|-m||Warn about multiple inclusion. This option causes makedepend to produce a warning if any input file includes another file more than once. In previous versions of makedepend this was the default behavior; the default has been changed to better match the behavior of the C compiler, which does not consider multiple inclusion to be an error. This option is provided for backward compatibility, and to aid in debugging problems related to multiple inclusion.|
|-- options --|
|If makedepend encounters a double hyphen (--) in the argument list, then any unrecognized argument following it will be silently ignored; a second double hyphen terminates this special treatment. In this way, makedepend can be made to safely ignore esoteric compiler arguments that might normally be found in a CFLAGS make macro (see the EXAMPLE section above). All options that makedepend recognizes and appear between the pair of double hyphens are processed normally.|
Given these assumptions, makedepend expects to be called once for each makefile, with all source files that are maintained by the makefile appearing on the command line. It parses each source and include file exactly once, maintaining an internal symbol table for each. Thus, the first file on the command line will take an amount of time proportional to the amount of time that a normal C preprocessor takes. But on subsequent files, if it encounters an include file that it has already parsed, it does not parse it again.
For example, imagine you are compiling two files, file1.c and file2.c, they each include the header file header.h, and the file header.h in turn includes the files def1.h and def2.h. When you run the command
makedepend file1.c file2.c
makedepend will parse file1.c and consequently, header.h and then def1.h and def2.h. It then decides that the dependencies for this file are
file1.o: header.h def1.h def2.h
But when the program parses file2.c and discovers that it, too, includes header.h, it does not parse the file, but simply adds header.h, def1.h and def2.h to the list of dependencies for file2.o.
Imagine you are parsing two files, say file1.c and file2.c, each includes the file def.h. The list of files that def.h includes might truly be different when def.h is included by file1.c than when it is included by file2.c. But once makedepend arrives at a list of dependencies for a file, it is cast in concrete.