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Full Discussion: makefile ifeq not working
Top Forums Programming makefile ifeq not working Post 302350084 by Corona688 on Wednesday 2nd of September 2009 06:35:29 PM
Old 09-02-2009
Makefiles do not work that way, they are not shell scripts. They are a list of what files you need to build what files. if you tell it b comes from a, c comes from b, and d comes from c, give it a, then ask for d, it will execute the given instructions in the order needed to produce the target. You can specify them in any order.

Targets you build do not affect variables. These control structures you're trying are more like #ifdef's in C, if you know how those work.

A statement like
Code:
a:b
        echo "creating file a"
        cp b a

...specifies files and only files. It specifies that to create file a, you must have file b. You cannot use it to assign a variable -- and that's probably a good thing since that would botch horribly if make tried to do things in parallel. The lines below it, which must begin in tabs, are shell statements that specify how to create file a. They are executed individually and in order when make tries to build target 'a'.

Remember, you can specify these relationships in any order, and the makefile will decide what statements it needs to do in order to create a from b, c from a, d from c, and so forth. This means it must read and parse the entire file before doing anything, it is not a shell script. It won't even have started building by the time it reaches @echo "regress == YES" because it parses the entire file before deciding what targets to build in what order, and statements in them cannot affect the make environment anyway since they are executed in a shell.

Last edited by Corona688; 09-02-2009 at 07:43 PM..
 

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gccmakedep(1)						      General Commands Manual						     gccmakedep(1)

NAME
gccmakedep - create dependencies in makefiles using 'gcc -M' SYNOPSIS
gccmakedep [ -sseparator ] [ -fmakefile ] [ -a ] [ -- options -- ] sourcefile ... DESCRIPTION
The gccmakedep program calls 'gcc -M' to output makefile rules describing the dependencies of each sourcefile, so that make(1) knows which object files must be recompiled when a dependency has changed. By default, gccmakedep places its output in the file named makefile if it exists, otherwise Makefile. An alternate makefile may be speci- fied with the -f option. It first searches the makefile for a line beginning with # DO NOT DELETE or one provided with the -s option, as a delimiter for the dependency output. If it finds it, it will delete everything following this up 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 makefile and place the output after that. EXAMPLE
Normally, gccmakedep will be used in a makefile target so that typing 'make depend' will bring the dependencies up to date for the make- file. For example, SRCS = file1.c file2.c ... CFLAGS = -O -DHACK -I../foobar -xyz depend: gccmakedep -- $(CFLAGS) -- $(SRCS) OPTIONS
The program will ignore any option that it does not understand, so you may use the same arguments that you would for gcc(1), including -D and -U options to define and undefine symbols and -I to set the include path. -a Append the dependencies to the file instead of replacing existing dependencies. -fmakefile Filename. This allows you to specify an alternate makefile in which gccmakedep can place its output. Specifying "-" as the file name (that is, -f-) sends the output to standard output instead of modifying an existing file. -sstring Starting string delimiter. This option permits you to specify a different string for gccmakedep to look for in the makefile. The default is "# DO NOT DELETE". -- options -- If gccmakedep encounters a double hyphen (--) in the argument list, then any unrecognized arguments following it will be silently ignored. A second double hyphen terminates this special treatment. In this way, gccmakedep can be made to safely ignore esoteric compiler arguments that might normally be found in a CFLAGS make macro (see the EXAMPLE section above). -D, -I, and -U options appearing between the pair of double hyphens are still processed normally. SEE ALSO
gcc(1), make(1), makedepend(1). AUTHOR
gccmakedep was written by the XFree86 Project based on code supplied by Hongjiu Lu. Colin Watson wrote this manual page, originally for the Debian Project, based partly on the manual page for makedepend(1). XFree86 Version Version 4.3.0 gccmakedep(1)
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