Open External Input Dataset

cdds_in is called to initialize an input dictionary. A temporary dictionary name is returned, along with any dictionaries specified by the user/default. It provides the title and a copy of the bootstrap dictionaries (par:). The resulting dictionaries are left in "scan" mode.

This is normally followed by a call to cdds_open to open the binary stream associated with the dictionary.

in_dict = cdds_in("in", "stdin:", title);
in_bin = cdds_open(in_dict, "in_format", "in_data", "r");
if (in_bin < 0) {
   cdds_prterr("Unable to open input data\n");
}

cdds_scanf("size.axis(1)", "%d", &ns);
    

Another example is to open a velocity file with no default.

vel_dict = cdds_in("vel", " ", title);
vel_bin = cdds_open(vel_dict, "vel_format", "vel_data", "r");
    

Open Internal Buffer

A dataset may not be in a host-dependent format with which a program can work. So an internal buffer binary must be defined and opened. This is done creating a temporary internal buffer dictionary and defining the desired fields in a host-dependent format (typically "asp" and then opening the binary stream. You can write modification definitions to the "override:" internal dictionary via the "MOD_FIELD" definition. (See Process Data to see how to map the input buffer to this internal buffer.)

/* "override:" overrides any existing definitions. */
cdds_dict("override:", "print");

cdds_printf("MOD_FIELD", "*+ int StaCor;\n");
cdds_printf(" ", "*+ float SrcX;\n");
cdds_printf(" ", "*+ SAMPLE_TYPE Samples[axis_size(1)];\n");

cdds_printf("fmt:*:asp.SAMPLE_TYPE", 
          "typedef float SAMPLE_TYPE;\n");
    

The application can open binary data using this internal "asp" format. The open mode is "m" (memory), because external I/O to a stream is not required. The data will only reside within buffers provided by the application (buf) or by cdds_write.

int buf_bin;
const char *buf_dict;
...
/* Initialize "buf_dict" dictionary */
buf_dict = cdds_out(" ", " ", in_dict);
cdds_printf("buf_format", " asp\n");
            
/* Open "buf" binary (see "override:") */
buf_bin = cdds_open(buf_dict, "buf_format", " ", "m");

/* close out the override: dictionary */
cdds_dict("override:", "reset");

    

Access Internal Buffer Fields

There are several ways to access fields within the internal buffer.

• Retrieve the index to a specific field:

  int tag, sxindex, smpindex;
  float srcx, *buf;
  ...
  tag = cdds_member(buf_bin, 0, "SrcX");
  sxindex = cdds_index(buf_bin, tag, DDS_FLOAT);
  tag = cdds_member(buf_bin, 0, "Samples");
  smpindex = cdds_index(buf_bin, tag, DDS_FLOAT);
  ...
  srcx = buf[sxindex];
  process(buf[smpindex), ...);
  ...
  buf[sxindex] = srcx;
          

• Rerieve the field value by tag:

  stacortag = cdds_member(buf_bin, 0, "StaCor");
  ...
  cdds_geti(buf_bin, stacortag, buf, 0, stacor, 1);