OpenCV build Error: libwebp.so not found - linux

Question

I have two Arch Linux machines on one I can compile my code but on my new one I get the following errors:
:-1: warning: libwebp.so.5, needed by /usr/local/lib/libopencv_imgcodecs.so, not found (try using -rpath or -rpath-link)
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPEncodeBGRA'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPDecodeBGRAInto'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPEncodeLosslessBGR'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPDecodeBGRInto'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPEncodeLosslessBGRA'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPGetFeaturesInternal'
/usr/local/lib/libopencv_imgcodecs.so:-1: error: undefined reference to `WebPEncodeBGR'
:-1: error: collect2: error: ld returned 1 exit status
My .pro file looks like this:
#-------------------------------------------------
#
# Project created by QtCreator 2015-11-15T16:30:56
#
#-------------------------------------------------
QT += core gui opengl
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = ColonyCounter
TEMPLATE = app
CONFIG += c++11
INCLUDEPATH += /usr/local/include/opencv
LIBS += -L/usr/local/lib -lopencv_core -lopencv_imgcodecs -lopencv_imgproc
SOURCES += main.cpp\
mainwindow.cpp \
cellcounter.cpp
HEADERS += mainwindow.h \
cellcounter.h
FORMS += mainwindow.ui
DISTFILES += \
to-do.txt
How can I link the library or something like this, haven't found anything in the web right know.
I have checked my libs and found out that I do not have a libwep.so.5 but libwebp.so.6 and libwebp.so and libwebp.so.2, but I do not know how to fix it, install libwebp.so.5 or change something in my .pro file?

Answer 1

Looks like the version of OpenCV that you installed wants to link with an older version of libwebp (specifically version 0.4.4 which contains libwebp.so.5) than what you have installed (probably version 0.5.0-1). Some options are:
Downgrade libwebp to 0.4.4 and ignore libwebp 0.5.0-1 to avoid reverting back with future upgrades. This is probably not the best choice, but it is easy and would work unless you have other packages which depend on 0.5.0-1.
Manually download and build the 0.4.4 version of libwebp and install in a non-standard location. In this case, you would need to modify/use LD_LIBRARY_PATH to point opencv there. This is probably your easiest best option.
Download some more recent version of the OpenCV source and build it. It will find and link to your current libwep.so.6, if it is compatible. The latest version of OpenCV (as of this writing 3.1.0) is compatible. This option is the best option but the most involved as compiling OpenCV can be trivial or painful depending upon the features you want to include.
Now a comment about your currently marked solution: Making a link from one soname to another is highly not recommended. In many cases, it won't compile, but even if it does, your application may exhibit arbitrary and unstable behavior and/or segfault unless the binaries are completely compatible. But if they were compatible, the packager would probably not have changed the soname. If this is for a school project, you might be ok, but if this is for anything important, don't do it.
Hope this helps.

Answer 2

I solved the problem with a not so elegant solution:
I just created a symbolic link:
$ file libwebp.so.5
libwebp.so.5: symbolic link to libwebp.so.6.0.0
with:
ln /usr/lib/libwebp.so.6 /usr/lib/libwebp.so.5