Geert JM Vanderkelen

You are using MySQL Cluster and crazy enough to digest NDB API? Sick of SQL? Here’s a treat: a function to make C/C++ strings ready for inserting into a VARCHAR field. The special thing about them is that the length is prefixed in the first 2 bytes.

void make_ndb_varchar(char *buffer, char *str)
{
  int len = strlen(str);
  int hlen = (len > 255) ? 2 : 1;
  buffer[0] = len & 0xff;
  if( len > 255 )
    buffer[1] = (len / 256);
  strcpy(buffer+hlen, str);
}

Yes, you can use memcpy. Whatever floats your boat.

Lets use this function for a table t1, defined as follows (note: latin1!):

CREATE TABLE t1 (
  id INT UNSIGNED NOT NULL,
  vc VARCHAR(128),
  vclong VARCHAR(1280),
  PRIMARY KEY (id)
  ) ENGINE=NDB DEFAULT CHARSET=latin1

Here is part of the code, simplified for this post:

 char vc[128+1]; // Size of 'vc', +1 for length info
 char vclong[1280+2]; // Size of 'vclong', +2 for length info
 ..
 make_ndb_varchar(vc, "NDB API kicks ass");
 operation->setValue("vc", vc);
 ..

The above example uses latin1. You could use Unicode, but that would probably mean converting from one encoding to the other using iconv. That’s another story.

This post complements Johan Andersson’s blog entry. Thanks to my colleagues Mats and Roger who helped me with a silly problem today regarding this function.