MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix D: Data Types

64-Bit Integer Structures

The C type for the SQL_C_SBIGINT and SQL_C_UBIGINT data type identifiers on Microsoft C compilers is _int64. When a compiler other than a Microsoft® C compiler is used, the C type might be different. If the compiler supports 64-bit integers natively, the driver or application should define ODBCINT64 to be the native 64-bit integer type. If the compiler does not support 64-bit integers natively, an application or driver can define the following structures to ensure that it has access to this data:

typedef struct{
SQLUINTEGER dwLowWord;
SQLUINTEGER dwHighWord;
} SQLUBIGINT

typedef struct{
SQLUINTEGER dwLowWord;
SQLINTEGER sdwHighWord;
} SQLBIGINT

These structures should be aligned to an 8-byte boundary because a 64-bit integer is aligned to the 8-byte boundary.