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BUGS
See the chapter "Problems and BUGS" in The GNU Make Manual.
AUTHOR
This manual page contributed by Dennis Morse of Stanford University. It has been reworked by Roland McGrath.
GNU, 22 August 1989
makedepend—Create dependencies in makeFILES
SYNOPSIS
makedepend [ _Dname=def ][_Dname ][_Iincludedir ][_Yincludedir ][_a ] [_fmakefile ][_oobjsuffix ][_pobjprefix ][_sstring ][_wwidth ][_v ][_m ] [__otherOPTIONS __ ] sourcefile . . .
DESCRIPTION
makedepend reads each sourcefile in sequence and parses it like a C-preprocessor, processing all #include, #define, #undef, #ifdef, #ifndef, #endif, #if and #else directives so that it can correctly tell which #include, directives would be used in a compilation. Any #include, directives can reference FILES having other #include directives, and parsing will occur in these FILES as well.
Every file that a source file 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 doesn't 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.
Example
Normally, makedepend will be used in a makefile target so that typing makedepend will bring the dependencies up-to-date for the makefile. For example,
SRCS = file1.c file2.c . . . CFLAGS = _O _DHACK _I../foobar _xyz depend: makedepend __ $(CFLAGS) __ $(SRCS)
OPTIONS
makedepend will ignore any option that it does not understand so that you may use the same arguments that you would for cc(1).
| _Dname=def or | Define. This places a definition for name in makedepend's symbol table. Without =def, the symbol becomes |
| _Dname | defined as 1. |
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| _Iincludedir | 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). |
| _Yincludedir | 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. |
| _fmakefile | Filename. This allows you to specify an alternate makefile in which makedepend can place its output. |
| _oobjsuffix | 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. |
| _pobjprefix | 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. |
| _sstring | 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 on standard output. |
| _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 backwards 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 preceding "Example" section.) All OPTIONS that makedepend recognizes and that appear between the pair of double hyphens are processed normally. |
Algorithm
The approach used in this program enables it to run an order of magnitude faster than any other dependency generator I have ever seen. Central to this performance are two assumptions: that all FILES compiled by a single makefile will be compiled with roughly the same -I and -D OPTIONS; and that most FILES in a single directory will include largely the same FILES.
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 both 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.
SEE ALSO
cc(1), make(1)