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## SQLite C Interface

## Obtaining SQL Values

>     const void *sqlite3_value_blob(sqlite3_value*);
>     double sqlite3_value_double(sqlite3_value*);
>     int sqlite3_value_int(sqlite3_value*);
>     sqlite3_int64 sqlite3_value_int64(sqlite3_value*);
>     void *sqlite3_value_pointer(sqlite3_value*, const char*);
>     const unsigned char *sqlite3_value_text(sqlite3_value*);
>     const void *sqlite3_value_text16(sqlite3_value*);
>     const void *sqlite3_value_text16le(sqlite3_value*);
>     const void *sqlite3_value_text16be(sqlite3_value*);
>     int sqlite3_value_bytes(sqlite3_value*);
>     int sqlite3_value_bytes16(sqlite3_value*);
>     int sqlite3_value_type(sqlite3_value*);
>     int sqlite3_value_numeric_type(sqlite3_value*);
>     int sqlite3_value_nochange(sqlite3_value*);
>     int sqlite3_value_frombind(sqlite3_value*);

Summary:

> sqlite3_value_blob | → | BLOB value
> sqlite3_value_double | → | REAL value
> sqlite3_value_int | → | 32-bit INTEGER value
> sqlite3_value_int64 | → | 64-bit INTEGER value
> sqlite3_value_pointer | → | Pointer value
> sqlite3_value_text | → | UTF-8 TEXT value
> sqlite3_value_text16 | → | UTF-16 TEXT value in the native byteorder
> sqlite3_value_text16be | → | UTF-16be TEXT value
> sqlite3_value_text16le | → | UTF-16le TEXT value
> sqlite3_value_bytes | → | Size of a BLOB or a UTF-8 TEXT in bytes
> sqlite3_value_bytes16 | → | Size of UTF-16 TEXT in bytes
> sqlite3_value_type | → | Default datatype of the value
> sqlite3_value_numeric_type | → | Best numeric datatype of the value
> sqlite3_value_nochange | → | True if the column is unchanged in an UPDATE against a virtual table.
> sqlite3_value_frombind | → | True if value originated from a bound parameter

Details:

These routines extract type, size, and content information from protected sqlite3_value objects. Protected sqlite3_value objects are used to pass parameter information into the functions that implement application-defined SQL functions and virtual tables.

These routines work only with protected sqlite3_value objects. Any attempt to use these routines on an unprotected sqlite3_value is not threadsafe.

These routines work just like the corresponding column access functions except that these routines take a single protected sqlite3_value object pointer instead of a sqlite3_stmt* pointer and an integer column number.

The sqlite3_value_text16() interface extracts a UTF-16 string in the native byte-order of the host machine. The sqlite3_value_text16be() and sqlite3_value_text16le() interfaces extract UTF-16 strings as big-endian and little-endian respectively.

If sqlite3_value object V was initialized using sqlite3_bind_pointer(S,I,P,X,D) or sqlite3_result_pointer(C,P,X,D) and if X and Y are strings that compare equal according to strcmp(X,Y), then sqlite3_value_pointer(V,Y) will return the pointer P. Otherwise, sqlite3_value_pointer(V,Y) returns a NULL. The sqlite3_bind_pointer() routine is part of the pointer passing interface added for SQLite 3.20.0.

The sqlite3_value_type(V) interface returns the datatype code for the initial datatype of the sqlite3_value object V. The returned value is one of SQLITE_INTEGER, SQLITE_FLOAT, SQLITE_TEXT, SQLITE_BLOB, or SQLITE_NULL. Other interfaces might change the datatype for an sqlite3_value object. For example, if the datatype is initially SQLITE_INTEGER and sqlite3_value_text(V) is called to extract a text value for that integer, then subsequent calls to sqlite3_value_type(V) might return SQLITE_TEXT. Whether or not a persistent internal datatype conversion occurs is undefined and may change from one release of SQLite to the next.

The sqlite3_value_numeric_type() interface attempts to apply numeric affinity to the value. This means that an attempt is made to convert the value to an integer or floating point. If such a conversion is possible without loss of information (in other words, if the value is a string that looks like a number) then the conversion is performed. Otherwise no conversion occurs. The datatype after conversion is returned.

Within the xUpdate method of a virtual table, the sqlite3_value_nochange(X) interface returns true if and only if the column corresponding to X is unchanged by the UPDATE operation that the xUpdate method call was invoked to implement and if the prior xColumn method call that was invoked to extract the value for that column returned without setting a result (probably because it queried sqlite3_vtab_nochange() and found that the column was unchanging). Within an xUpdate method, any value for which sqlite3_value_nochange(X) is true will in all other respects appear to be a NULL value. If sqlite3_value_nochange(X) is invoked anywhere other than within an xUpdate method call for an UPDATE statement, then the return value is arbitrary and meaningless.

The sqlite3_value_frombind(X) interface returns non-zero if the value X originated from one of the sqlite3_bind() interfaces. If X comes from an SQL literal value, or a table column, or an expression, then sqlite3_value_frombind(X) returns zero.

Please pay particular attention to the fact that the pointer returned from sqlite3_value_blob(), sqlite3_value_text(), or sqlite3_value_text16() can be invalidated by a subsequent call to sqlite3_value_bytes(), sqlite3_value_bytes16(), sqlite3_value_text(), or sqlite3_value_text16().

These routines must be called from the same thread as the SQL function that supplied the sqlite3_value* parameters.

As long as the input parameter is correct, these routines can only fail if an out-of-memory error occurs while trying to do a UTF8→UTF16 or UTF16→UTF8 conversion. If an out-of-memory error occurs, then the return value from these routines is the same as if the column had contained an SQL NULL value. If the input sqlite3_value was not obtained from sqlite3_value_dup(), then valid SQL NULL returns can also be distinguished from out-of-memory errors after extracting the value by invoking the sqlite3_errcode() immediately after the suspicious return value is obtained and before any other SQLite interface is called on the same database connection. If the input sqlite3_value was obtained from sqlite3_value_dup() then it is disconnected from the database connection and so sqlite3_errcode() will not work. In that case, the only way to distinguish an out-of-memory condition from a true SQL NULL is to invoke sqlite3_value_type() on the input to see if it is NULL prior to trying to extract the value.

See also lists of Objects, Constants, and Functions.