android studio 3.0.1 encounter error

[Kanbo0409]

@moli232777144 compile your mtcnn_AS project via android studio 3.0.1, encounter error as flollow:
Error:error: linker command failed with exit code 1 (use -v to see invocation), how can I solvesit ?

[moli232777144]

more details？

[Kanbo0409]

Executing tasks: [clean, :app:assembleDebug]

Configuration on demand is an incubating feature.
Configuration 'compile' in project ':app' is deprecated. Use 'implementation' instead.
Configuration 'androidTestCompile' in project ':app' is deprecated. Use 'androidTestImplementation' instead.
Configuration 'testCompile' in project ':app' is deprecated. Use 'testImplementation' instead.
:clean
:app:externalNativeBuildCleanDebug
Clean mtcnn armeabi-v7a,libncnn armeabi-v7a
Cleaning... 2 files.
:app:externalNativeBuildCleanRelease
Clean mtcnn armeabi-v7a,libncnn armeabi-v7a
Cleaning... 0 files.
:app:clean
:app:preBuild UP-TO-DATE
:app:preDebugBuild
:app:compileDebugAidl
:app:compileDebugRenderscript
:app:checkDebugManifest
:app:generateDebugBuildConfig
:app:prepareLintJar UP-TO-DATE
:app:generateDebugResValues
:app:generateDebugResources
:app:mergeDebugResources
:app:createDebugCompatibleScreenManifests
:app:processDebugManifest
:app:splitsDiscoveryTaskDebug
:app:processDebugResources
:app:generateDebugSources
:app:javaPreCompileDebug
:app:compileDebugJavaWithJavac
:app:generateJsonModelDebug UP-TO-DATE
:app:externalNativeBuildDebug
Build mtcnn armeabi-v7a
[1/3] Building CXX object CMak
eFiles/mtcnn.dir/src/main/cpp/mtcnn.cpp.o
[2/3] Building CXX ob
ject CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn_jni.cpp.o
[3/3] Linking CX
X shared library ........\build\intermediates\cmake\debug\obj\arm
eabi-v7a\libmtcnn.so
FAILED: cmd.exe /C "cd . && C:\Users\sfzhou\AppData\Local\Android\Sdk\ndk-bundle\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe --target=armv7-none-linux-androideabi --gcc-toolchain=C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64 --sysroot=C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sysroot -fPIC -isystem C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sysroot/usr/include/arm-linux-androideabi -D__ANDROID_API__=17 -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -mthumb -Wa,--noexecstack -Wformat -Werror=format-security -std=c++11 -fopenmp -O2 -fvisibility=hidden -fvisibility-inlines-hidden -fomit-frame-pointer -fstrict-aliasing -ffunction-sections -fdata-sections -ffast-math -std=c++11 -frtti -fexceptions -O0 -fno-limit-debug-info -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libatomic.a -nostdlib++ --sysroot C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/platforms/android-17/arch-arm -Wl,--build-id -Wl,--warn-shared-textrel -Wl,--fatal-warnings -Wl,--fix-cortex-a8 -Wl,--exclude-libs,libunwind.a -LC:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a -Wl,--no-undefined -Wl,-z,noexecstack -Qunused-arguments -Wl,-z,relro -Wl,-z,now -shared -Wl,-soname,libmtcnn.so -o ........\build\intermediates\cmake\debug\obj\armeabi-v7a\libmtcnn.so CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn.cpp.o CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn_jni.cpp.o ../../../../src/main/jniLibs/armeabi-v7a/libncnn.a -ljnigraphics -lz -llog -latomic -lm "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_static.a" "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++abi.a" "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libandroid_support.a" "C:/Users/sfzhou
/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libunwind.a" "-ldl" && cd ."
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Blob* std::__uninitialized_copy_a<ncnn::Blob*, ncnn::Blob*, ncnn::Blob>(ncnn::Blob*, ncnn::Blob*, ncnn::Blob*, std::allocatorncnn::Blob&) [clone .isra.107]: error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::find_blob_index_by_name(char const*) const: error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::find_layer_index_by_name(char const*) const: error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jni
Libs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Extractor::input(char const*, ncnn::Mat const&): error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Layer*, std::allocatorncnn::Layer* >::resize(unsigned int, ncnn::Layer*): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::layer_registry_entry, std::allocatorncnn::layer_registry_entry >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::layer_registry_entry*, std::vector<ncnn::layer_registry_entry, std::allocatorncnn::layer_registry_entry > >, unsigned int, ncnn::layer_registry_entry const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Layer*, std::allocatorncnn::Layer* >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Layer**, std::vector<ncnn::Layer*, std::allocatorncnn::Layer* > >, unsigned int, ncnn::Layer* const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<int, std::allocator >::_M_fill_insert(__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator > >, unsigned int, int const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Extractor::extract(char const*, ncnn::Mat&): error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: un
defined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/ma
in/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::resize(unsigned int, ncnn::Blob): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
:app:externalNativeBuildDebug FAILED

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':app:externalNativeBuildDebug'.

Build command failed.
Error while executing process C:\Users\sfzhou\AppData\Local\Android\Sdk\cmake\3.6.4111459\bin\cmake.exe with arguments {--build D:\sfzhou\github\mtcnn_ncnn-master\mtcnn_AS\app.externalNativeBuild\cmake\debug\armeabi-v7a --target mtcnn}
[1/3] Building CXX object CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn.cpp.o
[2/3] Building CXX object CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn_jni.cpp.o
[3/3] Linking CXX shared library ........\build\intermediates\cmake\debug\obj\armeabi-v7a\libmtcnn.so
FAILED: cmd.exe /C "cd . && C:\Users\sfzhou\AppData\Local\Android\Sdk\ndk-bundle\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe --target=armv7-none-linux-androideabi --gcc-toolchain=C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64 --sysroot=C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sysroot -fPIC -isystem C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sysroot/usr/include/arm-linux-androideabi -D__ANDROID_API__=17 -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -mthumb -Wa,--noexecstack -Wformat -Werror=format-security -std=c++11 -fopenmp -O2 -fvisibility=hidden -fvisibility-inlines-hidden -fomit-frame-pointer -fstrict-aliasing -ffunction-sections -fdata-sections -ffast-math -std=c++11 -frtti -fexceptions -O0 -fno-limit-debug-info -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libatomic.a -nostdlib++ --sysroot C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/platforms/android-17/arch-arm -Wl,--build-id -Wl,--warn-shared-textrel -Wl,--fatal-warnings -Wl,--fix-cortex-a8 -Wl,--exclude-libs,libunwind.a -LC:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a -Wl,--no-undefined -Wl,-z,noexecstack -Qunused-arguments -Wl,-z,relro -Wl,-z,now -shared -Wl,-soname,libmtcnn.so -o ........\build\intermediates\cmake\debug\obj\armeabi-v7a\libmtcnn.so CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn.cpp.o CMakeFiles/mtcnn.dir/src/main/cpp/mtcnn_jni.cpp.o ../../../../src/main/jniLibs/armeabi-v7a/libncnn.a -ljnigraphics -lz -llog -latomic -lm "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++_static.a" "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libc++abi.a" "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libandroid_support.a" "C:/Users/sfzhou/AppData/Local/Android/Sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/libunwind.a" "-ldl" && cd ."
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Blob* std::__uninitialized_copy_a<ncnn::Blob*, ncnn::Blob*, ncnn::Blob>(ncnn::Blob*, ncnn::Blob*, ncnn::Blob*, std::allocatorncnn::Blob&) [clone .isra.107]: error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::clear(): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_M_destroy(std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::~Net(): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::find_blob_index_by_name(char const*) const: error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::find_layer_index_by_name(char const*) const: error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Extractor::input(char const*, ncnn::Mat const&): error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Layer*, std::allocatorncnn::Layer* >::resize(unsigned int, ncnn::Layer*): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::layer_registry_entry, std::allocatorncnn::layer_registry_entry >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::layer_registry_entry*, std::vector<ncnn::layer_registry_entry, std::allocatorncnn::layer_registry_entry > >, unsigned int, ncnn::layer_registry_entry const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Layer*, std::allocatorncnn::Layer* >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Layer**, std::vector<ncnn::Layer*, std::allocatorncnn::Layer* > >, unsigned int, ncnn::Layer* const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<int, std::allocator >::_M_fill_insert(__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator > >, unsigned int, int const&): error: undefined reference to 'std::__throw_length_error(char const*)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Extractor::extract(char const*, ncnn::Mat&): error: undefined reference to 'std::string::compare(char const*) const'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::_M_fill_insert(__gnu_cxx::__normal_iterator<ncnn::Blob*, std::vector<ncnn::Blob, std::allocatorncnn::Blob > >, unsigned int, ncnn::Blob const&): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function std::vector<ncnn::Blob, std::allocatorncnn::Blob >::resize(unsigned int, ncnn::Blob): error: undefined reference to 'std::string::_Rep::_S_empty_rep_storage'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::string::assign(std::string const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
../../../../src/main/jniLibs/armeabi-v7a/libncnn.a(net.cpp.o):net.cpp:function ncnn::Net::load_param(__sFILE*): error: undefined reference to 'std::basic_string<char, std::char_traits, std::allocator >::basic_string(char const*, std::allocator const&)'
clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.

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BUILD FAILED in 14s

20 actionable tasks: 18 executed, 2 up-to-date

[moli232777144]

You may not have installed correct c++ environment.so links to third-party libraries to fail.

[Kanbo0409]

How Should I install C++ environments?

[wwmoo7]

i have same issue , i build the libcnn.a and replace it , and then the error is fix.

[wzc118]

I have the same problem,how to solve it?