Why am I getting the error, "undefined reference to `pow' collect2: error: ld returned 1 exit status make: *** [p1] Error 1"?

Question

Here is my makefile:

CC=gcc 

CFLAGS=-g

LDFLAGS=-lm

EXECS= p1


all: $(EXECS)

clean: 
    rm -f *.o $(EXECS)

14:32:16 **** Build of configuration Default for project CH3-Programs **** make p1 gcc -g -ggdb -lm p1.c -o p1 /tmp/ccNTyUSA.o: In function main': /home/bm5788/fromVM/Workspace/CH3-Programs//p1.c:28: undefined reference topow' collect2: error: ld returned 1 exit status make: *** [p1] Error 1 : recipe for target 'p1' failed

And the makefile will build the executable `p1` from what object files? And please post the output from running the `make` command (after `make clean`). — Some programmer dude, Sep 21 '16 at 18:28
I mean, you say that `all` depend on $(EXECS)` (i.e. `p1`). But what does `$(EXECS)` depend on? — Some programmer dude, Sep 21 '16 at 18:35
I was told that as long as I have the -lm then it should link math.h. — Bryce Marshall, Sep 21 '16 at 18:41
in which folder do you have math.h and in which folder do you have your code — Angen, Sep 21 '16 at 18:45

Some programmer dude · Answer 1 · 2016-09-22T07:46:21.523

The problem here is the order you link with the math library (the -lm option). Libraries should be after the sources or object files on the command line when building.

So if you ran the command to build manually, it should look like

gcc p1.c -o p1 -lm

The problem is that your makefile doesn't really do anything, and it lives on implicit rules alone. The implicit rules use certain variables in a certain order which do not place the library in the right position in your makefile.

Try instead something like this makefile:

# The C compiler to use.
CC = gcc

# The C compiler flags to use.
# The -g flag is for adding debug information.
# The -Wall flag is to enable more warnings from the compiler
CFLAGS = -g -Wall

# The linker flags to use, none is okay.
LDFLAGS = 

# The libraries to link with.
LDLIBS = -lm

# Define the name of the executable you want to build.
EXEC = p1

# List the object files needed to create the executable above.
OBJECTS = p1.o

# Since this is the first rule, it's also the default rule to make
# when no target is specified. It depends only on the executable
# being built.
all: $(EXEC)

# This rule tells make that the executable being built depends on
# certain object files. This will link using $(LDFLAGS) and $(LDLIBS).
$(EXEC): $(OBJECTS)

# No rule needed for the object files. The implicit rules used
# make together with the variable defined above will make sure
# they are built with the expected flags.

# Target to clean up. Removes the executable and object files.
# This target is not really necessary but is common, and can be
# useful if special handling is needed or there are many targets
# to clean up.
clean:
    -rm -f *.o $(EXEC)

If you run make using the above makefile, the make program should first build the object file p1.o from the source file p1.c. Then is should use the p1.o object file to link the executable p1 together with the standard math library.

Yes!! It worked! Thank you very much. I can't thank you enough. — Bryce Marshall, Sep 21 '16 at 19:08
@BryceMarshall You can thank the answerer more effectively by upvoting and accepting his answer :-) — njuffa, Sep 21 '16 at 19:09

Why am I getting the error, "undefined reference to `pow' collect2: error: ld returned 1 exit status make: *** [p1] Error 1"?

1 Answers1