Help with -D flag in make file

emp · #1 07-Jul-2008, 13:38

I am using GNU compiler on redhat linux.

I used the -D flag in my makefile to set a #define.

it is used -DDEBUG_FLAG etc etc

In my code where I specify

#ifdef DEBUG_FLAG
do debug printing
#else
print "debug _flag is off"
#endif

If the -DDEBUG_FLAG is in the make file the code compiles and runs as expected.
When I remove the -DDEBUG_FLAG I get a compiler error that the variable DEBUG_FLAG is unidentified. at the #ifdef statement.

I want a global flag set and thought this was the easiest way to implement it. Any suggestions to get what I have implemented to work??

Or alternative suggestions.

Thanks

EMP

Peter_APIIT · #2 07-Jul-2008, 21:55

Please post your code and complete make file to here with code tags surrounded.

davekw7x · #3 07-Jul-2008, 22:40

Quote:

Originally Posted by emp

I am using GNU compiler on redhat linux...I used the -D flag in my makefile to set a #define...

Sounds like a reasonable thing to try. Here's how I might do it. (There are, undoubtedly, other ways.)

CPP / C++ / C Code:

/* testflag.c
 *
 * Reports whether something was defined at
 * compile time
 *
 */

#include <stdio.h>

int main()
{

#ifdef DEBUG_FLAG
    printf("DEBUG_FLAG is defined.\n");
#else
    printf("DEBUG_FLAG is not defined.\n");
#endif

    return 0;
}

Here's the Makefile:

Code:


CC      = gcc
CFLAGS  = -Wall -W -pedantic

FLAG    = -DDEBUG_FLAG
CFLAGS += $(FLAG)

TARGET = testflag

$(TARGET): $(TARGET).c
	@echo "In Makefile: FLAG = <$(FLAG)>"
	$(CC) $(CFLAGS) $< -o $@

clean:
	rm -f $(TARGET)

Here's what happens when I make it and execute

Code:

$ make clean; make && ./testflag
rm -f testflag
In Makefile: FLAG = <-DDEBUG_FLAG>
gcc -Wall -W -pedantic -DDEBUG_FLAG testflag.c -o testflag
DEBUG_FLAG is defined.

Now comment out the FLAG line in the Makefile:

Code:

#FLAG    = -DDEBUG_FLAG

Then

Code:

$ make clean; make && ./testflag
rm -f testflag
In Makefile: FLAG = <>
gcc -Wall -W -pedantic  testflag.c -o testflag
DEBUG_FLAG is not defined.

Now, leave it commented out and change the command line to make:

Code:

$ make clean; make FLAG="-DDEBUG_FLAG"  && ./testflag
rm -f testflag
In Makefile: FLAG = <-DDEBUG_FLAG>
gcc -Wall -W -pedantic -DDEBUG_FLAG testflag.c -o testflag
DEBUG_FLAG is defined.

Regards,

Dave

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Help with -D flag in make file

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Re: Help with -D flag in make file