ndk 中std::string 转 jstring 代码

可以使用以下代码将 std::string 转换为 jstring：

jstring stringToJstring(JNIEnv* env, const std::string& str) {
    return env->NewStringUTF(str.c_str());
}

其中，env 是 JNIEnv 指针，str 是要转换的 std::string 对象。该函数将 std::string 转换为 const char*，然后使用 NewStringUTF 函数将其转换为 jstring 对象。

相关问题

如何在Android Studio中配置NDK？

在Android Studio中配置NDK的步骤如下：

1.下载NDK：打开Android Studio，依次点击File -> Project Structure -> SDK Location，在SDK Location窗口中找到Android NDK location，点击Download按钮下载NDK。

2.配置NDK路径：下载完成后，回到SDK Location窗口，将下载好的NDK路径复制到Android NDK location中。

3.配置build.gradle文件：在app目录下的build.gradle文件中添加以下代码：

android {
    ...
    defaultConfig {
        ...
        externalNativeBuild {
            cmake {
                cppFlags ""
                abiFilters ""
            }
        }
    }
    ...
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

4.配置CMakeLists.txt文件：在项目根目录下创建CMakeLists.txt文件，并添加以下代码：

cmake_minimum_required(VERSION 3.4.1)

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because system libraries are included in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.
find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in the
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

5.编写C++代码：在app/src/main/cpp目录下创建native-lib.cpp文件，并添加以下代码：

#include <jni.h>
#include <string>

extern "C" JNIEXPORT jstring JNICALL
Java_com_example_ndkdemo_MainActivity_stringFromJNI(
        JNIEnv* env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

6.运行程序：点击Android Studio中的Run按钮，即可在模拟器或真机上运行程序。

E:\android\SDK\ndk\25.1.8937393\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++.exe --target=aarch64-none-linux-android21 --sysroot=E:/android/SDK/ndk/25.1.8937393/toolchains/llvm/prebuilt/windows-x86_64/sysroot -Dprac071301_EXPORTS -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security -std=c++11 -fno-limit-debug-info -fPIC -MD -MT CMakeFiles/prac071301.dir/native-lib.cpp.o -MF CMakeFiles\prac071301.dir\native-lib.cpp.o.d -o CMakeFiles/prac071301.dir/native-lib.cpp.o -c "F:/android studio project/prac071301/app/src/main/cpp/native-lib.cpp" F:/android studio project/prac071301/app/src/main/cpp/native-lib.cpp:28:31: error: too few arguments to function call, expected 2, have 1 env->NewString("���Ϻ�"); ~~~~~~~~~~~~~~ ^ E:/android/SDK/ndk/25.1.8937393/toolchains/llvm/prebuilt/windows-x86_64/sysroot/usr/include/jni.h:827:13: note: 'NewString' declared here jstring NewString(const jchar* unicodeChars, jsize len) ^

这个错误提示是因为`NewString`函数需要两个参数，但是你只传递了一个参数。正确的调用方式应该是`env->NewString(unicodeChars, len)`，其中`unicodeChars`是一个`jchar`类型的数组，`len`是数组的长度。你需要检查一下你的代码，确保传递了正确的参数。