build the example with ncnn

[zineos]

I want to build the ncnn shared library and use it.

the modified part in src/CMakeLists.txt is show below

#add_library(ncnn STATIC ${ncnn_SRCS})
add_library(ncnn SHARED ${ncnn_SRCS})
if(NCNN_OPENMP AND OpenMP_CXX_FOUND)
if(NCNN_CMAKE_VERBOSE)
message("Building with OpenMP")
endif()
target_link_libraries(ncnn PUBLIC OpenMP::OpenMP_CXX)
endif()

if(COVERAGE)
target_compile_options(ncnn PRIVATE --coverage)
endif()

#install(TARGETS ncnn ARCHIVE DESTINATION lib)
install(TARGETS ncnn LIBRARY DESTINATION lib)
install(FILES
allocator.h
blob.h
cpu.h
layer.h
layer_type.h
mat.h
modelbin.h
net.h
opencv.h
paramdict.h
benchmark.h
${CMAKE_CURRENT_BINARY_DIR}/layer_type_enum.h
${CMAKE_CURRENT_BINARY_DIR}/platform.h
DESTINATION include
)

---

and the error happen

[ 81%] Linking CXX shared library libncnn.so
[ 81%] Built target ncnn
Scanning dependencies of target fasterrcnn
[ 82%] Building CXX object examples/CMakeFiles/fasterrcnn.dir/fasterrcnn.cpp.o
/data/backup/ncnn-master/examples/fasterrcnn.cpp:46:0: warning: ignoring #pragma omp parallel [-Wunknown-pragmas]
#pragma omp parallel sections
^
/data/backup/ncnn-master/examples/fasterrcnn.cpp:48:0: warning: ignoring #pragma omp section [-Wunknown-pragmas]
#pragma omp section
^
/data/backup/ncnn-master/examples/fasterrcnn.cpp:52:0: warning: ignoring #pragma omp section [-Wunknown-pragmas]
#pragma omp section
^
[ 83%] Linking CXX executable fasterrcnn
CMakeFiles/fasterrcnn.dir/fasterrcnn.cpp.o: In function main': fasterrcnn.cpp:(.text.startup+0x314): undefined reference to ncnn::Net::Net()'
fasterrcnn.cpp:(.text.startup+0x32a): undefined reference to ncnn::Net::load_param(char const*)' fasterrcnn.cpp:(.text.startup+0x339): undefined reference to ncnn::Net::load_model(char const*)'
fasterrcnn.cpp:(.text.startup+0x3b0): undefined reference to ncnn::Mat::from_pixels_resize(unsigned char const*, int, int, int, int, int, ncnn::Allocator*)' fasterrcnn.cpp:(.text.startup+0x3e1): undefined reference to ncnn::Mat::substract_mean_normalize(float const*, float const*)'
fasterrcnn.cpp:(.text.startup+0x4ac): undefined reference to ncnn::Net::create_extractor() const' fasterrcnn.cpp:(.text.startup+0x4d0): undefined reference to ncnn::Extractor::input(char const*, ncnn::Mat const&)' fasterrcnn.cpp:(.text.startup+0x4f0): undefined reference to ncnn::Extractor::input(char const*, ncnn::Mat const&)' fasterrcnn.cpp:(.text.startup+0x584): undefined reference to ncnn::Extractor::extract(char const*, ncnn::Mat&)'
fasterrcnn.cpp:(.text.startup+0x5a4): undefined reference to ncnn::Extractor::extract(char const*, ncnn::Mat&)' fasterrcnn.cpp:(.text.startup+0x63f): undefined reference to ncnn::Net::create_extractor() const'
fasterrcnn.cpp:(.text.startup+0x6dc): undefined reference to ncnn::Extractor::input(char const*, ncnn::Mat const&)' fasterrcnn.cpp:(.text.startup+0x6ee): undefined reference to ncnn::Extractor::input(char const*, ncnn::Mat const&)' fasterrcnn.cpp:(.text.startup+0x771): undefined reference to ncnn::Extractor::extract(char const*, ncnn::Mat&)' fasterrcnn.cpp:(.text.startup+0x783): undefined reference to ncnn::Extractor::extract(char const*, ncnn::Mat&)'
fasterrcnn.cpp:(.text.startup+0x108f): undefined reference to ncnn::Net::~Net()' fasterrcnn.cpp:(.text.startup+0x1aba): undefined reference to ncnn::Net::~Net()'
collect2: error: ld returned 1 exit status
examples/CMakeFiles/fasterrcnn.dir/build.make:98: recipe for target 'examples/fasterrcnn' failed
make[2]: *** [examples/fasterrcnn] Error 1
CMakeFiles/Makefile2:99: recipe for target 'examples/CMakeFiles/fasterrcnn.dir/all' failed
make[1]: *** [examples/CMakeFiles/fasterrcnn.dir/all] Error 2
Makefile:127: recipe for target 'all' failed
make: *** [all] Error 2

---

how can I solve this problem

[nihui]

build ncnn as static library
ncnn ABI is not stable enough, that's why we provide static library only.