Result Values From A Query

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SQLite C Interface

Result Values From A Query

const void *sqlite3_column_blob(sqlite3_stmt*, int iCol);
int sqlite3_column_bytes(sqlite3_stmt*, int iCol);
int sqlite3_column_bytes16(sqlite3_stmt*, int iCol);
double sqlite3_column_double(sqlite3_stmt*, int iCol);
int sqlite3_column_int(sqlite3_stmt*, int iCol);
sqlite3_int64 sqlite3_column_int64(sqlite3_stmt*, int iCol);
const unsigned char *sqlite3_column_text(sqlite3_stmt*, int iCol);
const void *sqlite3_column_text16(sqlite3_stmt*, int iCol);
int sqlite3_column_type(sqlite3_stmt*, int iCol);
sqlite3_value *sqlite3_column_value(sqlite3_stmt*, int iCol);

These routines return information about a single column of the current result row of a query. In every case the first argument is a pointer to the prepared statement that is being evaluated (the sqlite3_stmt* that was returned from sqlite3_prepare_v2() or one of its variants) and the second argument is the index of the column for which information should be returned. The leftmost column of the result set has the index 0. The number of columns in the result can be determined using sqlite3_column_count().

If the SQL statement does not currently point to a valid row, or if the column index is out of range, the result is undefined. These routines may only be called when the most recent call to sqlite3_step() has returned SQLITE_ROW and neither sqlite3_reset() nor sqlite3_finalize() have been called subsequently. If any of these routines are called after sqlite3_reset() or sqlite3_finalize() or after sqlite3_step() has returned something other than SQLITE_ROW, the results are undefined. If sqlite3_step() or sqlite3_reset() or sqlite3_finalize() are called from a different thread while any of these routines are pending, then the results are undefined.

The sqlite3_column_type() routine returns the datatype code for the initial data type of the result column. The returned value is one of SQLITE_INTEGER, SQLITE_FLOAT, SQLITE_TEXT, SQLITE_BLOB, or SQLITE_NULL. The value returned by sqlite3_column_type() is only meaningful if no type conversions have occurred as described below. After a type conversion, the value returned by sqlite3_column_type() is undefined. Future versions of SQLite may change the behavior of sqlite3_column_type() following a type conversion.

If the result is a BLOB or UTF-8 string then the sqlite3_column_bytes() routine returns the number of bytes in that BLOB or string. If the result is a UTF-16 string, then sqlite3_column_bytes() converts the string to UTF-8 and then returns the number of bytes. If the result is a numeric value then sqlite3_column_bytes() uses sqlite3_snprintf() to convert that value to a UTF-8 string and returns the number of bytes in that string. If the result is NULL, then sqlite3_column_bytes() returns zero.

If the result is a BLOB or UTF-16 string then the sqlite3_column_bytes16() routine returns the number of bytes in that BLOB or string. If the result is a UTF-8 string, then sqlite3_column_bytes16() converts the string to UTF-16 and then returns the number of bytes. If the result is a numeric value then sqlite3_column_bytes16() uses sqlite3_snprintf() to convert that value to a UTF-16 string and returns the number of bytes in that string. If the result is NULL, then sqlite3_column_bytes16() returns zero.

The values returned by sqlite3_column_bytes() and sqlite3_column_bytes16() do not include the zero terminators at the end of the string. For clarity: the values returned by sqlite3_column_bytes() and sqlite3_column_bytes16() are the number of bytes in the string, not the number of characters.

Strings returned by sqlite3_column_text() and sqlite3_column_text16(), even empty strings, are always zero-terminated. The return value from sqlite3_column_blob() for a zero-length BLOB is a NULL pointer.

Warning: The object returned by sqlite3_column_value() is an unprotected sqlite3_value object. In a multithreaded environment, an unprotected sqlite3_value object may only be used safely with sqlite3_bind_value() and sqlite3_result_value(). If the unprotected sqlite3_value object returned by sqlite3_column_value() is used in any other way, including calls to routines like sqlite3_value_int(), sqlite3_value_text(), or sqlite3_value_bytes(), the behavior is not threadsafe.

These routines attempt to convert the value where appropriate. For example, if the internal representation is FLOAT and a text result is requested, sqlite3_snprintf() is used internally to perform the conversion automatically. The following table details the conversions that are applied:

Internal
Type Requested
Type Conversion

NULL INTEGER Result is 0
NULL FLOAT Result is 0.0
NULL TEXT Result is a NULL pointer
NULL BLOB Result is a NULL pointer
INTEGER FLOAT Convert from integer to float
INTEGER TEXT ASCII rendering of the integer
INTEGER BLOB Same as INTEGER->TEXT
FLOAT INTEGER CAST to INTEGER
FLOAT TEXT ASCII rendering of the float
FLOAT BLOB CAST to BLOB
TEXT INTEGER CAST to INTEGER
TEXT FLOAT CAST to REAL
TEXT BLOB No change
BLOB INTEGER CAST to INTEGER
BLOB FLOAT CAST to REAL
BLOB TEXT Add a zero terminator if needed

Internal Type	Requested Type	Conversion
NULL	INTEGER	Result is 0
NULL	FLOAT	Result is 0.0
NULL	TEXT	Result is a NULL pointer
NULL	BLOB	Result is a NULL pointer
INTEGER	FLOAT	Convert from integer to float
INTEGER	TEXT	ASCII rendering of the integer
INTEGER	BLOB	Same as INTEGER->TEXT
FLOAT	INTEGER	CAST to INTEGER
FLOAT	TEXT	ASCII rendering of the float
FLOAT	BLOB	CAST to BLOB
TEXT	INTEGER	CAST to INTEGER
TEXT	FLOAT	CAST to REAL
TEXT	BLOB	No change
BLOB	INTEGER	CAST to INTEGER
BLOB	FLOAT	CAST to REAL
BLOB	TEXT	Add a zero terminator if needed

Note that when type conversions occur, pointers returned by prior calls to sqlite3_column_blob(), sqlite3_column_text(), and/or sqlite3_column_text16() may be invalidated. Type conversions and pointer invalidations might occur in the following cases:

The initial content is a BLOB and sqlite3_column_text() or sqlite3_column_text16() is called. A zero-terminator might need to be added to the string.
The initial content is UTF-8 text and sqlite3_column_bytes16() or sqlite3_column_text16() is called. The content must be converted to UTF-16.
The initial content is UTF-16 text and sqlite3_column_bytes() or sqlite3_column_text() is called. The content must be converted to UTF-8.

Conversions between UTF-16be and UTF-16le are always done in place and do not invalidate a prior pointer, though of course the content of the buffer that the prior pointer references will have been modified. Other kinds of conversion are done in place when it is possible, but sometimes they are not possible and in those cases prior pointers are invalidated.

The safest policy is to invoke these routines in one of the following ways:

sqlite3_column_text() followed by sqlite3_column_bytes()
sqlite3_column_blob() followed by sqlite3_column_bytes()
sqlite3_column_text16() followed by sqlite3_column_bytes16()

In other words, you should call sqlite3_column_text(), sqlite3_column_blob(), or sqlite3_column_text16() first to force the result into the desired format, then invoke sqlite3_column_bytes() or sqlite3_column_bytes16() to find the size of the result. Do not mix calls to sqlite3_column_text() or sqlite3_column_blob() with calls to sqlite3_column_bytes16(), and do not mix calls to sqlite3_column_text16() with calls to sqlite3_column_bytes().

The pointers returned are valid until a type conversion occurs as described above, or until sqlite3_step() or sqlite3_reset() or sqlite3_finalize() is called. The memory space used to hold strings and BLOBs is freed automatically. Do not pass the pointers returned from sqlite3_column_blob(), sqlite3_column_text(), etc. into sqlite3_free().

If a memory allocation error occurs during the evaluation of any of these routines, a default value is returned. The default value is either the integer 0, the floating point number 0.0, or a NULL pointer. Subsequent calls to sqlite3_errcode() will return SQLITE_NOMEM.

See also lists of Objects, Constants, and Functions.