Question

I wrote a program (myreader.c) to manipulate a RFID reader.

I compile by type “make” in the root of the package, makefile is shown below

  # CC and CFLAGS are varilables 
  CC=gcc
  CFLAGS = -c
  # -c option ask g++ to compile the source files, but do not link.
  # -g option is for debugging version
  # -O2 option is for optimized version
  OPTFLAGS = -O2 -g

  myreader    : src/myreader.c
          $(CC) $(OPTFLAGS) src/myreader.c src/crypto1.c src/nfc-utils.c -lnfc -o ./bin/myreader 

  # clean all the .o and executable files
  clean:
          rm -rf bin/myreader

and it works well on my original machine(64 bits, Ubuntu 12.04 LTS), and the only problem is, when I type make, the warning info would come up.

  src/myreader.c:519:6: warning: conflicting types for ‘printResult’ [enabled by default]
  src/myreader.c:211:3: note: previous implicit declaration of ‘printResult’ was here

But /bin/myreader works well.

---

However, when I move the package to another machine(64 bits, Ubuntu 11.10), and type make in the same way as in the original machine.

Error messages in the below appears:

  berln@ubuntu:~/桌面/useful code$ make
  gcc -O2 -g src/myreader.c src/crypto1.c src/nfc-utils.c -lnfc -o ./bin/myreader
  src/myreader.c:519:6: warning: conflicting types for ‘printResult’ [enabled by default]
  src/myreader.c:211:3: note: previous implicit declaration of ‘printResult’ was here
  /tmp/ccrKvhjm.o: In function `mf_enhanced_auth':/home/berln/桌面/useful code/src/myreader.c:373: undefined reference to `nfc_configure'
  /home/berln/桌面/useful code/src/myreader.c:380: undefined reference to `nfc_configure'
  /home/berln/桌面/useful code/src/myreader.c:390: undefined reference to `nfc_configure'
  /home/berln/桌面/useful code/src/myreader.c:434: undefined reference to `nfc_configure'
  /tmp/ccrKvhjm.o: In function `mf_configure':
  /home/berln/桌面/useful code/src/myreader.c:484: undefined reference to `nfc_configure'
  /tmp/ccrKvhjm.o:/home/berln/桌面/useful code/src/myreader.c:489: more undefined references to `nfc_configure' follow
  /tmp/ccrKvhjm.o: In function `main':
  /home/berln/桌面/useful code/src/myreader.c:155: undefined reference to `nfc_connect'
  /home/berln/桌面/useful code/src/myreader.c:213: undefined reference to `nfc_disconnect'
  collect2: ld returned 1 exit status
  make: *** [myreader] Error 1

I have no ideas why this error happened on only one machine instead of both.

If you need more information, you can download the package here.

Thanks in advance.

Answer 1

Most likely your nfc library is missing or not installed properly on your other computer.

One of the options you pass to the linker is -lnfc, which tells it to link to the nfc library. Your errors are coming from the linker, which cannot find the nfc_configure and other nfc_ symbols. This means that the linker cannot find these symbols. Check the nfc library installation.