error linking to LibPng library - linker

Question

I am having trouble linking to the libpng library.
The build seems unable to define references to Libpng calls.
I think the problem is in my Libpng install.
I am runing in the Mingw environment on a Win7 laptop
My build environment is as follows:
My path starts with C:\MinGW\bin;C:\MinGW\msys\1.0\bin;C:\MinGW\git\cmd;C:\Program Files
C:\Users\Bob\Home\png23d>g++ --version
g++ (GCC) 5.3.0
I have built and installed libpng-1.6.28 which creates the following:
C:\MinGW\bin>
libpng-config
libpng16-config
libpng16.dll
C:\MinGW\include\libpng
png.h
pngconf.h
pnglibconf.h
C:\MinGW\include\libpng16
png.h
pngconf.h
pnglibconf.h
C:\MinGW\lib\pkgconfig
C:\MinGW\lib>
libpng.a
libpng.dll.a
libpng16.a
libpng16.dll.a
a symbolic link `libpng' to `libpng16'
a symbolic link `libpng.pc' to `libpng16.pc'
a symbolic link `libpng.a' to `libpng16.a'
a symbolic link `libpng-config' to `libpng16-config
when I try to build a program "png23d" I get the following
C:\Users\Bob\Home\png23d>make
g++ -DUSE_LIBPNG -lpng png23d.o option.o bitmap.o mesh.o mesh_gen.o mesh_index.o mesh_simplify.o out_pgm.o out_rscad.o out_pscad.o out_stl.o -o png23d
bitmap.o:bitmap.c:(.text+0x102): undefined reference to `png_sig_cmp'
bitmap.o:bitmap.c:(.text+0x142): undefined reference to `png_create_read_struct'
.
.
.
bitmap.o:bitmap.c:(.text+0x418): undefined reference to `png_read_end'
bitmap.o:bitmap.c:(.text+0x466): undefined reference to `png_destroy_read_struct'
collect2.exe: error: ld returned 1 exit status
<builtin>: recipe for target 'png23d' failed
make: *** [png23d] Error 1
I am almost sure its the -lpng that is not working.... I am just don't know how to fix it.
I am guessing that it is a symbolic link problem and I know I did not create one during the libpng build.
If I am right what do I need to link it to.
I tried changing -lpng to -llpng16. It made no difference.
Thanks from the command prompt that work fine.
just have to figure out how to change the make file.
#!/usr/bin/make
#
# png23d is a program to convert png images into 3d files
#
# Copyright 2011 Vincent Sanders <vince#kyllikki.org>
#
# Released under the MIT License,
# http://www.opensource.org/licenses/mit-license.php
CC = g++
VERSION=100
PREFIX =
WARNFLAGS = -W -Wall -Wundef -Wpointer-arith \
-Wcast-align -Wwrite-strings -Wstrict-prototypes \
-Wmissing-prototypes -Wmissing-declarations -Wredundant-decls \
-Wnested-externs
ifneq ($(GCCVER),2)
WARNFLAGS += -Wno-unused-parameter
endif
OPTFLAGS=-O2
#OPTFLAGS=-O0
CFLAGS+=$(WARNFLAGS) -MMD -DVERSION=$(VERSION) $(OPTFLAGS) -g
LDFLAGS+= -DUSE_LIBPNG -lpng
PNG23D_OBJ=png23d.o option.o bitmap.o mesh.o mesh_gen.o mesh_index.o mesh_simplify.o out_pgm.o out_rscad.o out_pscad.o out_stl.o
.PHONY : all clean
all:png23d
png23d:$(PNG23D_OBJ)
-include $(PNG23D_OBJ:.o=.d)
-include test/Makefile.sub
clean: testclean
${RM} png23d $(PNG23D_OBJ) *.d *~ png23d.png
install:png23d
install -D png23d $(DESTDIR)$(PREFIX)/bin
install-man:png23d.1
install -D png23d.1 $(DESTDIR)$(PREFIX)/share/man/man1
# logo creation
png23d.png:png23d.pov
povray +L/usr/share/povray/include/ -D +Q11 +O$# +UV +UL +A0.2 +FP8 +W400 +H300 $<

Answer 1

Move -lpng to after the object files.