Question

I am new to C++ on linux enviroment and am trying to use the png++ library for a project. The problem I am facing is that that a simple program I write using png++ incudes does not work and shows me the following errors

AProg.o: In function `png::info_base::info_base(png::io_base&, png_struct_def*)':
AProg.cpp:(.text._ZN3png9info_baseC2ERNS_7io_baseEP14png_struct_def[_ZN3png9info_baseC5ERNS_7io_baseEP14png_struct_def]+0x21): undefined reference to `png_create_info_struct'
AProg.o: In function `png::info::write() const':
AProg.cpp:(.text._ZNK3png4info5writeEv[png::info::write() const]+0xd4): undefined reference to `png_set_PLTE'
AProg.cpp:(.text._ZNK3png4info5writeEv[png::info::write() const]+0x137): undefined reference to `png_set_tRNS'
AProg.cpp:(.text._ZNK3png4info5writeEv[png::info::write() const]+0x14f): undefined reference to `png_write_info'
AProg.o: In function `png::info::sync_ihdr() const':
AProg.cpp:(.text._ZNK3png4info9sync_ihdrEv[png::info::sync_ihdr() const]+0x79): undefined reference to `png_set_IHDR'
AProg.o: In function `png::end_info::destroy()':
AProg.cpp:(.text._ZN3png8end_info7destroyEv[png::end_info::destroy()]+0x48): undefined reference to `png_destroy_info_struct'
AProg.o: In function `png::end_info::write() const':
AProg.cpp:(.text._ZNK3png8end_info5writeEv[png::end_info::write() const]+0x1a): undefined reference to `png_write_end'
AProg.o: In function `png::io_base::set_swap() const':
AProg.cpp:(.text._ZNK3png7io_base8set_swapEv[png::io_base::set_swap() const]+0x1b): undefined reference to `png_set_swap'
.............. (and it goes on).

The background of what I have done so far.

1 : I have gcc/g++ configured correctly.

2 : I have correctly installed libpng-1.2.50. The result seems to be correct.

This is how my usr/local folder looks now

:/usr/local/include$ ls

libpng12  libpng15  png++  pngconf.h  png.h  pnglibconf.h

:/usr/local/lib$ ls

libpng12.a   libpng12.so    libpng12.so.0.50.0  libpng15.la  libpng15.so.15     libpng.a   libpng.so    libpng.so.3.50.0  python2.7
libpng12.la  libpng12.so.0  libpng15.a          libpng15.so  libpng15.so.15.12.0  libpng.la  libpng.so.3  pkgconfig

:/usr/local/bin$ ls

eclipse  libpng-1.2.50  libpng12-config  libpng-1.5.12  libpng15-config  libpng-config  png++-0.2.5

3 : After that I followed the following ( http://www.nongnu.org/pngpp/doc/0.2.5/ ) to install the png++-0.2.5 and all the five steps didnt gave any error.

But after that when I tried to compile a simple program (with the instructions given at the same site : http://www.nongnu.org/pngpp/doc/0.2.5/ ) it would not compile.

:~/workspace/AProg$ g++ -o AProg AProg.o 'libpng-config --ldflags'

g++: error: libpng-config --ldflags: No such file or directory

Then I tried to solve the problem and google it and gave this command which seems to work fine at compile but when I tried to run it. I got the error as mentioned at the top of the post

 :~/workspace/AProg$ g++ -c AProg.cpp -I/usr/local/include/libpng12 -L/usr/local/lib -lpng -I/usr/local/include/png++

 :~/workspace/AProg$ 

I am sorry for such a long post. But I just wanted to explain anything /everything related to my problem. Hope somebody helps me here.

Answer 1

It seems that the quotes you use in the linker command line is not the correct ones, it should be the single back quote:

$ g++ -o AProg AProg.o `libpng-config --ldflags`