android jni中读写文件的代码

读取文件：

JNIEXPORT jstring JNICALL
Java_com_example_myapplication_MainActivity_readFile(JNIEnv *env, jobject instance,
                                                      jstring fileName_) {
    const char *fileName = (*env)->GetStringUTFChars(env, fileName_, 0);

    FILE *file = fopen(fileName, "r");
    if (file == NULL) {
        return (*env)->NewStringUTF(env, "");
    }

    char buffer[1024];
    size_t len;
    char *result = (char *) malloc(1);
    result[0] = '\0';
    while ((len = fread(buffer, 1, sizeof(buffer), file)) > 0) {
        result = (char *) realloc(result, strlen(result) + len + 1);
        strncat(result, buffer, len);
    }

    fclose(file);

    (*env)->ReleaseStringUTFChars(env, fileName_, fileName);

    return (*env)->NewStringUTF(env, result);
}

写入文件：

JNIEXPORT jboolean JNICALL
Java_com_example_myapplication_MainActivity_writeFile(JNIEnv *env, jobject instance,
                                                       jstring fileName_, jstring content_) {
    const char *fileName = (*env)->GetStringUTFChars(env, fileName_, 0);
    const char *content = (*env)->GetStringUTFChars(env, content_, 0);

    FILE *file = fopen(fileName, "w");
    if (file == NULL) {
        return JNI_FALSE;
    }

    fwrite(content, strlen(content), 1, file);

    fclose(file);

    (*env)->ReleaseStringUTFChars(env, fileName_, fileName);
    (*env)->ReleaseStringUTFChars(env, content_, content);

    return JNI_TRUE;
}