Undefined reference for external library (C++, QT, Ubuntu 14, CCV)

Question

I'm trying to run the CCV library linked at http://libccv.org/ in QT Creator on Ubuntu 14. I followed this tutorial http://libccv.org/tutorial/ and I'm trying now to run the first simple example. I get these errors:

• error: undefined reference to ccv_read_impl(void const*, ccv_dense_matrix_t**, int, int, int, int)
• error: undefined reference to ccv_write(ccv_dense_matrix_t*, char*, int*, int, void*)

This is the .pro file of the project:

TEMPLATE = app
CONFIG += console
CONFIG -= app_bundle
CONFIG -= qt

SOURCES += main.cpp

unix:!macx: LIBS += -L$$PWD/../../../CNN/ccv/lib/ -lccv

INCLUDEPATH += $$PWD/../../../CNN/ccv/lib
DEPENDPATH += $$PWD/../../../CNN/ccv/lib

unix:!macx: PRE_TARGETDEPS += $$PWD/../../../CNN/ccv/lib/libccv.a

Finally this is the command generated by QT in the compile output:

• g++ -m64 -o ccv1 main.o -L/home/fabri/QT/CCV1/ccv1/../../../CNN/ccv/lib/ -lccv

I suppose it's a compiler problem but I don't know what. Thank you.

Answer 1

Modify the example and try to include it like this:

extern "C" {
#include "ccv.h"
}