指针注意

新分配的指针，移动前先保存 首地址，不然移动的最后，free(*p)会指错

-(NSData*)getImageData{
    UIImage *img = [UIImage imageNamed:@"img1_8"];
    CGImageRef imgRef =img.CGImage;

    
    NSData *data2 = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"img1_8" ofType:@"png"]];
    Byte *buf = calloc(1, data2.length);
    NSLog(@"%lu",sizeof(data2));
    [data2 getBytes:buf length:data2.length];
    Byte *buf1= buf;
    for (int i= 0 ; i<data2.length; ++i) {
        NSLog(@"%d=>[%x] ",i,*(buf++));
    }
    
    @try
    {
        
    }
    @catch(NSException * e) {
        
    }
    
    NSData*data  = [NSData dataWithBytes:buf length:data2.length];
    free(buf1);
    return data;
}