Compilation Errors While Building a C++ Project with Android NDK using CMake and Ninja on a Windows Platform: A Comprehensive Guide to Troubleshooting

If you’re a developer who’s ventured into the realm of Android app development using C++ with the Android NDK, you’re likely no stranger to the frustration that comes with compilation errors. In this article, we’ll delve into the common pitfalls and provide a step-by-step guide to resolving compilation errors when building a C++ project with Android NDK using CMake and Ninja on a Windows platform.

Understanding the Android NDK and CMake

The Android NDK is a toolkit that allows developers to create native Android apps using C++ and other languages. It provides a set of libraries and tools that enable you to access Android device functionality and optimize performance. CMake, on the other hand, is a build system generator that helps you create build files for your project. Ninja is a build tool that works in conjunction with CMake to build and compile your project.

Common Compilation Errors

Before we dive into the troubleshooting process, let’s take a look at some common compilation errors you may encounter when building a C++ project with Android NDK using CMake and Ninja on a Windows platform:

• undefined reference to `std::__1::basic_string, std::__1::allocator >::basic_string(char const*, std::__1::allocator const&)’
• error: ‘std::string’ has not been declared
• fatal error: ‘android/log.h’ file not found
• undefined reference to `android::Looper::prepare()
• error: expected ‘)’ before ‘;’ token
• error: ‘LOG_TAG’ was not declared in this scope

Troubleshooting Compilation Errors

To troubleshoot compilation errors, let’s follow a structured approach to identify and resolve the issues:

Step 1: Verify the Android NDK Installation

Make sure you have the Android NDK installed on your Windows machine. Check the Android Studio settings to ensure the NDK path is correctly set:

File > Settings > Appearance & Behavior > System Settings > Android SDK > SDK Tools > NDK

Verify that the NDK path is pointing to the correct location:

C:\Users\username\AppData\Local\Android\Sdk\ndk-bundle

Step 2: Review the CMakeLists.txt File

CMakeLists.txt is the configuration file that tells CMake how to build your project. Let’s review the file to ensure it’s correctly configured:

cmake_minimum_required(VERSION 3.10.2)

set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 21)

set(CMAKE_ANDROID_API 21)
set(CMAKE_ANDROID_ABI "armeabi-v7a;armeabi-v7l;arm64-v8a;x86;x86_64;mips;mips64;mips64el")

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_library(mylibrary SHARED src/main/cpp/mylibrary.cpp)

find_package(log-android REQUIRED)

target_link_libraries(mylibrary log-android)

In this example, we’re setting the Android API level to 21, and the ABI to include armeabi-v7a, armeabi-v7l, and other architectures. We’re also setting the C++ standard to 11 and requiring it. The `add_library` directive adds our shared library, and we’re linking it to the log-android library.

Step 3: Verify the Ninja Build File

Ninja is a build tool that generates the build files based on the CMake configuration. Let’s review the Ninja build file to ensure it’s correctly generated:

ninja -v

This command will run Ninja in verbose mode, showing you the build process. You can inspect the build file to ensure it’s correctly configured:

build.ninja:1:  RULE  CXX_COMPILER
build.ninja:2:    depfile = build.ninja.d
build.ninja:3:    deps = gcc
build.ninja:4:  BUILD  mylibrary: CXX_COMPILER mylibrary.cpp
build.ninja:5:    OBJECT_FILE = mylibrary.obj

Step 4: Inspect the Compilation Errors

undefined reference to `std::__1::basic_string, std::__1::allocator >::basic_string(char const*, std::__1::allocator const&)'

This error indicates that the compiler can’t find the `std::string` implementation. Let’s review our CMakeLists.txt file to ensure we’re including the necessary STL libraries:

target_link_libraries(mylibrary log-android ${ANDROID_STL_LIBRARIES})

By adding the ${ANDROID_STL_LIBRARIES} variable, we’re telling CMake to link our library to the Android STL implementation.

Step 5: Verify the Android.mk File

The Android.mk file is used by the Android NDK to build your native library. Let’s review the file to ensure it’s correctly configured:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE    := mylibrary
LOCAL_SRC_FILES := src/main/cpp/mylibrary.cpp
LOCAL_LDLIBS    := -llog

include $(BUILD_SHARED_LIBRARY)

In this example, we’re defining our local module as `mylibrary`, and specifying the source file and library dependencies.

Common Solutions to Compilation Errors

Here are some common solutions to compilation errors when building a C++ project with Android NDK using CMake and Ninja on a Windows platform:

Error	Solution
undefined reference to `std::__1::basic_string, std::__1::allocator >::basic_string(char const*, std::__1::allocator const&)	Include the Android STL libraries in your CMakeLists.txt file: `target_link_libraries(mylibrary log-android ${ANDROID_STL_LIBRARIES})`
error: ‘std::string’ has not been declared	Include the `` header file in your C++ code: `#include `
fatal error: ‘android/log.h’ file not found	Verify that the Android NDK path is correctly set in your CMakeLists.txt file: `set(CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION “clang”)`
undefined reference to `android::Looper::prepare()`	Include the Android Looper library in your CMakeLists.txt file: `target_link_libraries(mylibrary log-android android::Looper)`
error: expected ‘)’ before ‘;’ token	Check your C++ code for syntax errors, and ensure that all parentheses are correctly matched.
error: ‘LOG_TAG’ was not declared in this scope	Define the LOG_TAG macro in your C++ code: `#define LOG_TAG “mylibrary”`

Conclusion

Compilation errors can be frustrating, but by following this comprehensive guide, you should be able to identify and resolve common issues when building a C++ project with Android NDK using CMake and Ninja on a Windows platform. Remember to verify the Android NDK installation, review the CMakeLists.txt file, inspect the Ninja build file, and inspect the compilation errors. With practice and patience, you’ll become proficient in troubleshooting and resolving compilation errors, and you’ll be well on your way to creating high-performance native Android apps using C++.

Happy coding!

Frequently Asked Questions

Get answers to the most common compilation errors while building a C++ project with Android NDK using CMake and Ninja on a Windows platform.