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Undefined reference to sqrt

I have included math.h in 1.c and LDLIBS=-lm in the makefile.

1.c and 2.c are some of the files in current directory.

Make file is as follows:

dINES+=PROJECT_CONF_H=\"project-conf.h\"
CONTIKI_PROJECT = 1 2
all: $(CONTIKI_PROJECT)

CONTIKI = ../..

WITH_UIP6=1
UIP_CONF_IPV6=1

CFLAGS+= -DUIP_CONF_IPV6_RPL -DUIP_CONF_IPV6 -DWITH_UIP6
LDLIBS=-lm
ifdef PERIOD
CFLAGS=-DPERIOD=$(PERIOD)
endif    

include $(CONTIKI)/Makefile.include

I have read related stackoverflow question and answers but unable to understand why Undefined reference to sqrt.

Solution

  • First, notice that include $(CONTIKI)/Makefile.include could unset any settings you have made above. So we cannot debug your problem.

    Then, run make -p once to understand the builtin rules (assuming you are using GNU make). Be sure to read documentation of make. Run also make --trace and/or use remake (e.g. as remake -x) to debug your Makefile.

    Be aware that the order of program arguments to gcc matters a lot. Read first the Invoking GCC chapter of the documentation of gcc. You want to compile with -Wall -g (to get all warnings & debug info) which might be added to your CFLAGS+= line. Perhaps your
    CFLAGS=-DPERIOD=$(PERIOD) line should be CFLAGS+= -DPERIOD=$(PERIOD)

    Perhaps your LDLIBS=-lm line should be LIBES= -lm.

    The Undefined reference: sqrt message might be because your compilation command (run by make) has -lm missing or in the wrong order.