Dynamic Dependency Scan

Feature Description

The capability to determine the implicit dependencies between files, typically between source and header files. Built-in rules are provided for scanning many languages (C, C++, Fortran, ESQL/C, nroff/troff, and others). Users can define new scan strategies for other languages.

Impact

Productivity

• File scanning is built in to the engine level target update algorithm, scans files generated during the build as well as previously existing files. External add-on dependency generation tools cannot do this.
• Eases maintenance - no need to maintain header dependencies in the makefile.
• Source files and header changes do not require change to makefiles.
• Programmable scanner allows support of additional languages and customizations to the built-in scan strategies.

Build Accuracy

• Include file dependencies are kept accurate and up-to-date each time nmake is run. Errors introduced by manually maintaining the dependencies are avoided.
• Command line include files (such -I flags for C/C++ compilers) are automatically generated.

Consequence of Not Having the Feature

• Include file dependencies must be maintained by the developer, either manually or by adding an additional step of running another command to determine the dependencies. The additional maintenance is error prone and inefficient.

Examples

The following files are used in this example. a.c include a.h, which includes b.h, which includes c.h, which includes stdio.h.

/*** ./Makefile  ****/
.SOURCE.h : include0 include1 include2 include3 include4 include5
abc :: a.c 

/*** ./a.c ***/
#include "a.h"
int main() {
    printf("abc\n");
    return(0);
}

/*** include1/a.h ***/
#include "b.h"

/*** include2/b.h ***/
#include "c.h"

/*** include3/c.h ***/
#include <stdio.h>

The first example illustrates that nmake scans the source code, locates the necessary include files and constructs the proper -I list for the compile line. Note that the -I flags are not hard-coded in the makefile, the .SOURCE.h special atom tells nmake where to search for include files.

$ nmake
+ cc -O -Iinclude1 -Iinclude2 -Iinclude3 -I- -c a.c
+ cc -O -o abc a.o

If one of the include files is updated nmake will recompile the target. We will use the nmake -e option to get an explanation of why it is recompiling. This shows nmake is tracking changes to the include files without listing them in the makefile.

$ touch include2/b.h

$ nmake -e
include2/b.h [Aug 21 13:38:18 2003] has changed [Aug 21 13:37:45 2003]
. [Aug 21 13:38:13 2003] has changed [Aug 21 13:38:08 2003]
+ cc -O -Iinclude1 -Iinclude2 -Iinclude3 -I- -c a.c
+ cc -O -o abc a.o

We can add another header file and it will be picked up automatically with no makefile change. c.h now includes d.h which is in the include4 directory.

/*** c.h ***/
#include 
#include "d.h"

$ nmake -e
include3/c.h [Aug 21 14:07:02 2003] has changed [Aug 21 14:06:32 2003]
include3/c.h prerequisite include4/d.h added or re-ordered
include4/d.h [Aug 21 14:05:17 2003] has no previous state
. [Aug 21 14:06:50 2003] has changed [Aug 21 14:06:45 2003]
+ cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4 -I- -c a.c
+ cc -O -o abc a.o

Finally, instead of compiling the target we will use a different makefile to show a list of the implicit include files. $(!) is an automatic variable which expands to all the explicit and implicit file prerequisites of the current target. This illustrates exactly which prerequisite header files nmake found by scanning the code. Notice even the system include files are tracked.

/*** ./Makefile ***/
.SOURCE.h : include0 include1 include2 include3 include4 include5

abc : a.c
        : $(!)

$ nmake
+ : a.c include1/a.h include2/b.h include3/c.h include4/d.h /usr/inclu
de/stdio.h /usr/include/sys/va_list.h /usr/include/sys/feature_tests.h

Example using standard make tool

The following uses the standard make tool to build the same code. Notice the makefile is much more complicated and verbose.

First we'll build without the additional d.h include file.

##### ./makefile #####
CFLAGS = -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4

abc : a.o 
        cc $(CFLAGS) -o abc a.o

a.o : a.c include1/a.h include2/b.h include3/c.h \
        /usr/include/stdio.h /usr/include/sys/va_list.h \
        /usr/include/sys/feature_tests.h

$ make
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4  -c  a.c
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4 -o abc a.o

$ touch include2/b.h

$ make
cc -O -Iinclude1 -Iinclude2 -Iinclude3  -c  a.c
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -o abc a.o

When d.h is added the makefile is out-of-date.

$ make
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4  -c  a.c
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4 -o abc a.o

$ touch include4/d.h  

$ make
`abc' is up to date.

Oops, let's update the makefile.

##### ./makefile #####
CFLAGS = -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4

abc : a.o 
        cc $(CFLAGS) -o abc a.o

a.o : a.c include1/a.h include2/b.h include3/c.h include4/d.h \
        /usr/include/stdio.h /usr/include/sys/va_list.h \
        /usr/include/sys/feature_tests.h

$ make
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4  -c  a.c
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4 -o abc a.o

$ touch include4/d.h

$ make
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4  -c  a.c
cc -O -Iinclude1 -Iinclude2 -Iinclude3 -Iinclude4 -o abc a.o