Undefined reference to 'pow' even though -lm is a compile flag. [C]

Question

Any reason

cc -g -lm -DBLITZ_HOST_IS_LITTLE_ENDIAN

would produce an error with code using math.h? Is it possible there's a difference between GCC version 4.0.3 (documented working version) and version 4.6.3 (my current version)?

makefile and asm.c @ https://gist.github.com/3801291

This is on ubuntu 12.04

My terminal output is a comment in the gist.

Answer 1

Instead of

cc -g -lm -DBLITZ_HOST_IS_LITTLE_ENDIAN foo.c

Try:

cc -g -DBLITZ_HOST_IS_LITTLE_ENDIAN foo.c -lm

When the linker searches a library, it links in modules that contain definitions for previously-undefined symbols.

If the linker searches -lm before foo.o, then pow() is not yet undefined. Conversely, if foo.o comes first, it undefines pow(), which -lm can then resolve.

---

EDIT: To accomplish this advice in your makefile, make these changes:

CFLAGS=-g -DBLITZ_HOST_IS_LITTLE_ENDIAN
LDLIBS=-lm

...

asm: asm.c
        $(CC) $(CFLAGS) asm.c $(LDLIBS) -o asm