undefined reference to function in Eclipse CDT

Question

In my main.c program I include this library:

#include "coap_api.h"

That is also included in Properties -> C/C++ Build -> Settings -> Cross ARM GNU Assembler -> Includes

and

Properties -> C/C++ Build -> Settings -> Cross ARM C Compiler -> Includes

Building the project I got this error:

./src/main.o: In function `main':
/Users/joanet/Development/Embedded/eclipseWS/EHAL-master/ARM/Nordic/nRF51/ipv6_coap_server/Release/../src/main.c:708: undefined reference to `coap_init' 

I read in another post that I have to link the library (http://whatwouldnickdo.com/wordpress/328/eclipse-cdt-and-linux-libraries/)

I've tried to add the library with the name coap_api but I does not work

lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/bin/ld: cannot find -lcoap_api

in the compilation the coap directory is included:

arm-none-eabi-gcc -mcpu=cortex-m0 -mthumb -Os -fmessage-length=0 -fsigned-char -ffunction-sections -fdata-sections -Wall  -g -DBLE_STACK_SUPPORT_REQD -DNRF51 -D__CORTEX_M0 -DBOARD_PCA10028 -DSOFTDEVICE_PRESENT -DS110 -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/ipv6_coap_server/bsp -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/iot/ipv6_stack/pbuffer -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/util/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/drivers_nrf/hal/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/../../../ARM/CMSIS/CMSIS/Include/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/../../../ARM/Nordic/nRF51/CMSIS/include/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/softdevice/s110/headers/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/common/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_bas/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_dis/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/device_manager/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/softdevice/common/softdevice_handler/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/scheduler/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_error_log/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/drivers_nrf/ble_flash/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_debug_assert_handler/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/timer/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/gpiote/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/drivers_nrf/pstorage/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_dfu/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/bootloader_dfu/experimental/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/bootloader_dfu/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/../../../include/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_hids/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/../../../ARM/CMSIS/CMSIS_RTX/INC/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/trace/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/device/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_tps/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/button/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/device_manager/config/" -I"/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/ipv6_coap_client/src" -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/toolchain/gcc -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/libraries/mem_manager -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/ble/ble_services/ble_ipsp -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/iot/include -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/iot/ipv6_stack/include -I/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/nrf51_sdk/components/iot/coap -std=gnu99 -MMD -MP -MF"src/Vectors_nRF51.d" -MT"src/Vectors_nRF51.o" -c -o "src/Vectors_nRF51.o" "/Users/nullpointer/Development/Embedded/eclipseWS/EHAL-master-Hoan/ARM/Nordic/nRF51/src/Vectors_nRF51.c"

Answer 1

The line:

#include "coap_api.h"

does not include a library, it includes a header file containing declarations defined elsewhere. You do have to link the separately compiled object code containing those definitions.

If that is a library file, you need to set the library path in a similar manner to the include paths. If the library has a name of the GNU conventional form libXXX.a, then it is linked with the switch -lXXX, otherwise you must specify the complete file name.

If however the declarations in coap_api.h refer to definitions in source code form, then you must add the source to your project for separate compilation and linking.

Answer 2

You need to link generate object files from coap.c then either make a library from this .o or directly compile your project with this previously generated coap.o file.

You should read some documentation about Compiling and Linking. Here your compiler tells you that it has undefined reference to coap_init, which is effectively beeing called by your program and referenced by the coap_api.h file. The problem is that it cannot find the associated machine code. You may have included the coap.c directory, it's nothing more than a text file. You first need to compile it and then create a library which you link to the project or copy import the coap.c in your project so that it gets compiled with the rest of your work.