C++ preprocessor variable

Question

Hi guys I'm using the SKELETON_JAR variable on my c++ code in one header. However I want to allow the user to define the place of the jar in the compile time easily. I think the easiest way to do that is to put this define in makefile is that so?

#define SKELETON_JAR "./Util.jar"

??

Answer 1

Depending on your compiler, the normal way to do this is to use the compiler's -D flag in the makefile. For example:

MYFLAGS = -DSKELETON_JAR="foo"

then later on:

gcc $(MYFLAGS) $(OTHER_STUFF)

Answer 2

In your code:

#ifndef SKELETON_JAR
  #define SKELETON_JAR "./Util.jar" // default path
#endif

and then in the makefile use CPPFLAGS:=-DSKELETON_JAR="./Util.jar".

Of course you have to make sure CPPFLAGS are passed to the compiler as part of the compile rule which is the case if you're using the default implicit rules.

From GNU Make documentation:

Compiling C programs

n.o is made automatically from n.c with a command of the form `$(CC) -c $(CPPFLAGS) $(CFLAGS)'

Answer 3

Use compilation flags for same and define flag in Makefile.

Answer 4

Another method is to place the JAR path as an environment variable. Some platforms have a getenv function for retrieving environment variables.

You may want to consider allowing the User to change the path before execution, such as using a configuration file.