Eclipse C++ undefined reference

Question

I am trying to use libmodbus and i have the following :

extern "C" {
#include "modbus.h"
#include "modbus-tcp.h"
}

void executeMbus() {
    modbus_t *mb;
    uint16_t tab_reg[32];
    mb = modbus_new_tcp("127.0.0.1", 1502);
    modbus_connect(mb);

    /* Read 5 registers from the address 0 */
    modbus_read_registers(mb, 0, 5, tab_reg);

    modbus_close(mb);
    modbus_free(mb);
}

I have added the path to the library in C/C++ General -> Paths and Symbols GNU C++ and i added the path to the modbus lib. However i'm getting weird undefined reference for each modbus_ method. How can i fix it ?

What's the actual command line invoking the compiler? My guess is you failed to add the library objects to the object to link, only provided the search path for it. — YSC, Apr 12 '17 at 11:12
@YSC i586-poky-linux-g++ -lmraa -fno-use-linker-plugin "--sysroot=C:\\Users\\hdta\\workspace\\libs\\iot2000-sdk-windows-2.1.2.tar\\iot2000-sdk-windows-2.1.2/sysroots/i586-nlp-32-poky-linux" -o Iot2020WithMB example.o example.o: In function `executeMbus()': after that i just get undefined reference to all modbus_ methods — Chris Tanev, Apr 12 '17 at 11:13
Possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](http://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Mike Kinghan, Apr 12 '17 at 11:21

score 2 · Answer 1 · edited Apr 12 '17 at 11:27

2

For the library libmodus to be linked with your program, you need to:

Add the include path to the compiler settings C/C++ general -> Paths and Symbols -> Includes -> GNU C++
Add the library path to the linker settings C/C++ General -> Paths and Symbols -> Library Paths
Add the library object to the linker settings C/C++ Build -> Settings -> Tool Settings -> GCC C++ Linker -> Libraries

You did (1.) and (2.) but you also need to do (3.).

edited Apr 12 '17 at 11:27

Raxvan

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answered Apr 12 '17 at 11:22

YSC

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thanks for your input sir. One small problem is that in my case i use IOT2000 C++ Compiler , so i dont have the option to add libraries to the Linker(there is just General tab there). I guess i need to make another just C++ project – Chris Tanev Apr 12 '17 at 11:25
@ChrisTanev if your compiler is not known by Eclipse, it should provide you with the ability to provide custom command line arguments. What does the "General" tab look like? – YSC Apr 12 '17 at 22:17

Eclipse C++ undefined reference

1 Answers1