MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix D: Data Types
The identifiers for the binary ODBC SQL data types are:
SQL_BINARY
SQL_VARBINARY
SQL_LONGVARBINARY
The following table shows the ODBC C data types to which binary SQL data may be converted. For an explanation of the columns and terms in the table, see "Converting Data from SQL to C Data Types."
| C type identifier | Test | *TargetValuePtr | *StrLen_or_IndPtr | SQLSTATE |
| SQL_C_CHAR | (Byte length of data) * 2 < BufferLength
(Byte length of data) * 2 >= BufferLength |
Data Truncated data |
Length of data in bytes
Length of data in bytes |
n/a 01004 |
| SQL_C_WCHAR | (Character length of data) * 2 < BufferLength (Character length of data) * 2 >= BufferLength |
Data Truncated data |
Length of data in characters
Length of data in characters |
n/a 01004 |
| SQL_C_BINARY | Byte length of data <= BufferLength
Byte length of data > BufferLength |
Data Truncated data |
Length of data in bytes
Length of data in bytes |
n/a 01004 |
When binary SQL data is converted to character C data, each byte (8 bits) of source data is represented as two ASCII characters. These characters are the ASCII character representation of the number in its hexadecimal form. For example, a binary 00000001 is converted to "01" and a binary 11111111 is converted to "FF".
The driver always converts individual bytes to pairs of hexadecimal digits and terminates the character string with a null byte. Because of this, if BufferLength is even and is less than the length of the converted data, the last byte of the *TargetValuePtr buffer is not used. (The converted data requires an even number of bytes, the next-to-last byte is a null byte, and the last byte cannot be used.)
Note Application developers are discouraged from binding binary SQL data to a character C data type. This conversion is usually inefficient and slow.