Linker error linker input file unused because linking not done undefined reference to a function in that file

Question

I m having trouble with the linking of my files   Basically  my program consists of    The main program  gen1  gen1 - receives input sends to str2value for processing  outputs results str2value  breaks input into tokens using  tokenizer  determines what sort of processing to do to each token  and passes them off to str2num  or str2cmd  It then returns an array of the results  str2num - does some processing str2cmd - ditto author py - a python script that generates str2cmd c and str2cmd h from a header cmdTable h    I m pretty sure I have my includes right  I ve checked a couple of times  I ve also checked that there are no conditions  ifndef wrong in the headers   Here is my Makefile    CPP   g   -lserial CPP   g   -DTESTMODE C  gcc DEFINES   LURC CFLAGS   -Wall -fshort-enums -D  DEFINES  PROJECTFILES   gen1 cpp str2value o  STR2VALUEFILES   str2value cpp str2cmd o str2num o tokenizer o str2value h  gen1     PROJECTFILES            CPP    CFLAGS  -o gen1   PROJECTFILES     str2value o     STR2VALUEFILES          echo  str2value            CPP    CFLAGS  -c   STR2VALUEFILES   str2num o  str2num cpp  str2value h str2num hpp            C    CFLAGS  -c      tokenizer o  tokenizer cpp tokenizer hpp           CPP    CFLAGS  -c     str2cmd o   authorCMDs py cmdTable h         python authorCMDs py cmdTable h str2cmd  this uses the gcc -E cmdTable h -DLURC           C    CFLAGS  -c str2cmd c str2cmd h   TODO  add a thing that checks str2cmd h  c has not been modified by hand     PHONEY  clean clean          rm   o   PHONEY  all all          clear         make clean         make   Here is the output I recieve from make all   make clean make 1   Entering directory   home frames LURC gen1 gen1Source  rm   o make 1   Leaving directory   home frames LURC gen1 gen1Source  make make 1   Entering directory   home frames LURC gen1 gen1Source  python authorCMDs py cmdTable h str2cmd  this uses the gcc -E cmdTable h -DLURC str2cmd c and str2cmd h  generated from cmdTable h  gcc  -Wall -fshort-enums -DLURC -c str2cmd c str2cmd h gcc  -Wall -fshort-enums -DLURC -c str2num cpp str2value h str2num hpp g   -DTESTMODE -Wall -fshort-enums -DLURC -c tokenizer cpp tokenizer hpp g   -DTESTMODE -Wall -fshort-enums -DLURC -c str2value cpp str2cmd o str2num o tokenizer o str2value h g    str2cmd o  linker input file unused because linking not done g    str2num o  linker input file unused because linking not done g    tokenizer o  linker input file unused because linking not done g   -DTESTMODE -Wall -fshort-enums -DLURC -o gen1 gen1 cpp str2value o str2value o  In function  getValue char     str2value cpp   text 0xbd   undefined reference to  str2cmd char    str2value cpp   text 0x102   undefined reference to  str2num char    str2value o  In function  getAllValues char     str2value cpp   text 0x164   undefined reference to  tokenizer  tokenizer char    str2value cpp   text 0x177   undefined reference to  tokenizer  getNumTokens char const    str2value cpp   text 0x1a9   undefined reference to  tokenizer  getNextToken char const    str2value cpp   text 0x1e9   undefined reference to  tokenizer  getNumTokens char const    str2value cpp   text 0x201   undefined reference to  tokenizer   tokenizer    str2value cpp   text 0x25b   undefined reference to  tokenizer   tokenizer    collect2  ld returned 1 exit status make 1        gen1  Error 1 make 1   Leaving directory   home frames LURC gen1 gen1Source  make       all  Error 2   Any suggestions about what this is about  STR2VALUESFILES has all the object files I need  to define the missing functions

User · Accepted Answer

I think you are confused about how the compiler puts things together. When you use -c flag, i.e. no linking is done, the input is C++ code, and the output is object code. The .o files thus don't mix with -c, and compiler warns you about that. Symbols from object file are not moved to other object files like that.

All object files should be on the final linker invocation, which is not the case here, so linker (called via g++ front-end) complains about missing symbols.

Here's a small example (calling g++ explicitly for clarity):

PROG ?= myprog
OBJS = worker.o main.o

all: $(PROG)

.cpp.o:
        g++ -Wall -pedantic -ggdb -O2 -c -o $@ $<

$(PROG): $(OBJS)
        g++ -Wall -pedantic -ggdb -O2 -o $@ $(OBJS)

There's also makedepend utility that comes with X11 - helps a lot with source code dependencies. You might also want to look at the -M gcc option for building make rules.

[c++] Linker error: "linker input file unused because linking not done", undefined reference to a function in that file

Examples related to c++

Examples related to c

Examples related to gcc

Examples related to makefile

Examples related to linker-errors