deepstream-user-metadata-app limited to only char or int type metadata?

Accelerated Computing Intelligent Video Analytics DeepStream SDK
#1

I am trying to attach custom type metadata, like string in deepstream_sdk_v4.0_jetson/sources/apps/sample_apps/deepstream-user-metadata-test/deepstream_user_metadata_app.c . For this, I have modified the set_metadata function like this:

void *set_metadata_ptr()
{
  int i = 0;
  gchar *user_metadata = (gchar*)g_malloc0(USER_ARRAY_SIZE);
  
  char str[20] = "string";

  g_print("\n**************** Setting user metadata array of 16 on nvinfer src pad\n");
//  for(i = 0; i < USER_ARRAY_SIZE; i++) {
    user_metadata[0] = str;

    user_metadata[1] = 'K'; // works fine with single character or integer type variables

    g_print("user_meta_data [%d] = %s\n", 0, user_metadata[0]);

   g_print("user_meta_data [%d] = %c\n", 1, user_metadata[1]);
//  }
  return (void *)user_metadata;
}

It doesn’t work, results in segmentation fault. I need some different types of variable as user_metadata, like string or float. Could anyone suggest how to attach different type of variable like float, string etc as user_metadata?

#2

I think you cannot assign the char pointer to char type.
user_metadata[0] = str;

#3

For example, I want to attach float type variable. Why it’s not attaching float but attaching integer?

user_metadata[0] = (int) 156;

It works fine until the value is less than 255. But

user_metadata[0] = (float) 1.56;

It doesn’t work because the return value is always 0.00

#4

Hello,

You are trying to assign float to char. It won’t work. What do you expect to get back when you assign 1.56 to char?

#5

I wonder how int has been assigned to char as in this line?

user_metadata[0] = (int) 156;

How this is even working? Could you please explain? @mipko

#6

I think mipko has explained very clearly.
char only has 8 bit, so you can assign some int value to char, this is the basic syntax problem.

#7

char is 8-bit (1 byte) large. It can be observed as an int.
Depending if it is signed or unsigned it can hold following int values:

char	        1 byte	-128 to 127 or 0 to 255
unsigned char	1 byte	   0 to 255
signed char	1 byte	-128 to 127

So try to assign 4242 to user_metadata[0] and check what you get.

On the other hand float is 4 bytes long which means any float requires four elements of your array to represent that float.

float	4 byte	1.2E-38 to 3.4E+38	6 decimal places

At the end you could use your array to store floats with pointer arithmetic, but it is not the way you should do it. Nevertheless if you have N floating point numbers your array should be 4*N large.