int main(int argc, const char * argv[]) {

    // insert code here...

    string str3 = "/Users/Ethan/Downloads/aaa/platform-tools/adb shell screencap -p";

    NSMutableData *resultData=[[NSMutableData alloc] init];

    FILE * fstream = NULL;

    if(NULL==(fstream=popen(str3.c_str(),"r")))

    {

        fprintf(stderr,"execute command failed: %s",strerror(errno));

        return NULL;

    }

   FILE *png = fopen("/var/folders/_g/mmsygkld2sv2pl719654cscm0000gn/T/2.png", "w");

    char tmp[]; //存储每一行输出

    size_t all=;

    size_t readNum=fread(tmp,, sizeof(tmp)-, fstream);

    while (readNum!=)

    {

        if (tmp[readNum-] == 0xd)

        {

            tmp[readNum++] = fgetc(fstream);

        }

        for (unsigned int i = ; i < readNum; ++i) {

            if (tmp[i] == 0xd && tmp[i+] == 0xa ) {

                tmp[i] = 0xa;

                for (unsigned int j = i+; j < readNum - ; ++j)

                    tmp[j] = tmp[j+];

                readNum--;

            }

        }

         all=all+readNum;

        //写到文件

        fwrite(tmp, , readNum, png);

        //直接放到内存

        [resultData appendBytes:tmp length:readNum];

        readNum=fread(tmp,, sizeof(tmp)-, fstream);

    }

    NSImage *img=[[NSImage alloc] initWithData:resultData];

    NSLog(@"%f",img.size.width);

    return ;

}