C ++预处理器变量

Question

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

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

no is made automatically from nc with a command of the form `$(CC) -c $(CPPFLAGS) $(CFLAGS)'

Answer 2

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 3

在Makefile中使用相同的编译标志和define标志。