linker - Qt creator 5 link -

i have qtcreator 5 , want use libpng12-0 library. don't know how have link project ? there's problem when writte:

loadedimage = img_load(filename.c_str()); 

i know have writte like:

     libs += -l      libs += -libpng12-0 

does know have ?

i tried lot of things i'm new on qt creator 5. help. sorry english.

if need gui method then,

• open .pro file
• right click in text editor area
• choose add library
• then choose type of library
• provide path of library file
• done.

if directly want edit .pro file, library name -lpng12-0 not -libpng12-0 .