android 端java代码：
public class MainActivity extends AppCompatActivity {
private String SD_CARD_PATH;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
requestPermission();
SD_CARD_PATH= Environment.getExternalStorageDirectory().getAbsolutePath();
}
public void requestPermission() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED ||
ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

        Toast.makeText(this, "申请权限", Toast.LENGTH_SHORT).show();
        ActivityCompat.requestPermissions(this, new String[]{
                Manifest.permission.WRITE_EXTERNAL_STORAGE,
                Manifest.permission.READ_EXTERNAL_STORAGE}, 100);
    }
}
public void diff(View view) {
     String path=SD_CARD_PATH+ File.separatorChar+"video.mp4";
     String path_pattern=SD_CARD_PATH+File.separatorChar+"video_%d.mp4";
     NDKFileUtils.diff(path,path_pattern,3);
}
public void patch(View view) {
    String path=SD_CARD_PATH +File.separatorChar+ "video_%d.mp4";
    String merge_path = SD_CARD_PATH +File.separatorChar+ "video_merge.mp4";
    NDKFileUtils.patch(path,3,merge_path);
}

}
native 方法：
/**

• @Author: CHENGYUE
• @CreateDate: 2021/3/2
• @Email: chengyue@yibaishun.cn
• @Description: 类作用描述
  /
  public class NDKFileUtils {
  static {
  System.loadLibrary("native-lib");
  }
  /*
  • 拆分
  • @param path
  • @param path_pattern
  • @param count
    /
    public native static void diff(String path,String path_pattern,int count);
    /*
  • 合并
  • @param path
  • @param count
  • @param merge_path
    */
    public native static void patch(String path,int count,String merge_path);
    }

C++ 代码：

include <jni.h>

include <string>

include <stdio.h>

include <stdlib.h>

include <android/log.h>

define LOGI(FORMAT,...) __android_log_print(ANDROID_LOG_INFO,"chengyue",FORMAT,VA_ARGS)

define LOGE(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR,"chengyue",FORMAT,VA_ARGS)

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

long get_file_size(const char path){
FILE fp=fopen(path,"rb");
fseek(fp,0,SEEK_END);
return ftell(fp);
}
//拆分
extern "C" JNIEXPORT void JNICALL
Java_com_example_ndkcrypt_NDKFileUtils_diff(JNIEnv env, jclass clazz, jstring path_str,
jstring path_pattern_str, jint file_num) {
//需要分割的路径
const char path=env->GetStringUTFChars(path_str,NULL);
const char path_pattern =env->GetStringUTFChars(path_pattern_str,NULL);
//得到分割之后的子文件的路径列表
char patches = (char)malloc(sizeof(char) * file_num);
int i = 0;
for(;i<file_num;i++){
patches[i]=(char)malloc(sizeof(char) *100);
sprintf(patches[i],path_pattern,(i+1));
LOGI("patch path:%s",patches[i]);
}
//不断读取path文件，循环写入file_num个文件中
// 整除
// 文件大小：90，分成9个文件，每个文件10
// 不整除
// 文件大小：110，分成9个文件，
// 前(9-1)个文件为(110/(9-1))=13
// 最后一个文件(110%(9-1))=6
LOGI("path:%s",path);
int filesize=get_file_size(path);
LOGI("filesize:%d",filesize);
FILE *fpr = fopen(path,"rb");
//整除
if(filesize%file_num==0){
//单个文件
int part=filesize/file_num;
i=0;
//逐一写入不同的分割子文件
for(;i<file_num;i++){
FILE *fpw=fopen(patches[i],"wb");
int j=0;
for(;j<part;j++){
//边读边写
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}
} else{//不整除
int part=filesize/(file_num-1);
i=0;
for(;i< file_num - 1;i++){
FILE *fpw=fopen(patches[i],"wb");
int j=0;
for(;j<part;j++){
//边读边写
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}// the last one
FILE *fpw = fopen(patches[file_num - 1], "wb");
i = 0;
for(; i < filesize % (file_num - 1); i++){
fputc(fgetc(fpr),fpw);
}
fclose(fpw);
}
//关闭被分割的文件
fclose(fpr);
//释放
i = 0;
for(; i < file_num; i++){
free(patches[i]);
}
free(patches);
env->ReleaseStringUTFChars(path_str,path);
env->ReleaseStringUTFChars(path_pattern_str,path_pattern);
}
extern "C" JNIEXPORT void JNICALL
Java_com_example_ndkcrypt_NDKFileUtils_patch(JNIEnv *env, jclass clazz, jstring path_str, jint file_num,
jstring merge_path_str) {
//合并之后的文件
const char *merge_path=env->GetStringUTFChars(merge_path_str,NULL);
//分割的子文件
const char *path_pattern=env->GetStringUTFChars(path_str,NULL);

char **patches = (char**)malloc(sizeof(char*) * file_num);
int i = 0;
for (; i < file_num; i++) {
    patches[i] = (char*)malloc(sizeof(char) * 100);
    //元素赋值
    //需要分割的文件：C://jason/liuyan.png
    //子文件：C://jason/liuyan_%d.png
    sprintf(patches[i], path_pattern, (i+1));
    LOGI("patch path:%s",patches[i]);
}

FILE *fpw = fopen(merge_path,"wb");
//把所有的分割文件读取一遍，写入一个总的文件中
//把所有的分割文件读取一遍，写入一个总的文件中
i = 0;
for(; i < file_num; i++){
    //每个子文件的大小
    int filesize = get_file_size(patches[i]);
    FILE *fpr = fopen(patches[i], "rb");
    int j = 0;
    for (; j < filesize; j++) {
        fputc(fgetc(fpr),fpw);
    }
    fclose(fpr);
}
fclose(fpw);
LOGI("merge path:%s",merge_path);
//释放
i = 0;
for(; i < file_num; i++){
    free(patches[i]);
}
free(patches);
env->ReleaseStringUTFChars(path_str,path_pattern);
env->ReleaseStringUTFChars(merge_path_str,merge_path);

}