capi3.html

这是sqlite3.56的文档。拿来给大家阅读使用

</p>

<p>
After an SQL statement has been prepared (and optionally bound), it
is executed using:
</p>

<blockquote><pre>
   int sqlite3_step(sqlite3_stmt*);
</pre></blockquote>

<p>
The sqlite3_step() routine return SQLITE_ROW if it is returning a single
row of the result set, or SQLITE_DONE if execution has completed, either
normally or due to an error.  It might also return SQLITE_BUSY if it is
unable to open the database file.  If the return value is SQLITE_ROW, then
the following routines can be used to extract information about that row
of the result set:
</p>

<blockquote><pre>
   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);
   int sqlite3_column_count(sqlite3_stmt*);
   const char *sqlite3_column_decltype(sqlite3_stmt *, int iCol);
   const void *sqlite3_column_decltype16(sqlite3_stmt *, int iCol);
   double sqlite3_column_double(sqlite3_stmt*, int iCol);
   int sqlite3_column_int(sqlite3_stmt*, int iCol);
   long long int sqlite3_column_int64(sqlite3_stmt*, int iCol);
   const char *sqlite3_column_name(sqlite3_stmt*, int iCol);
   const void *sqlite3_column_name16(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);
</pre></blockquote>

<p>
The 
<a href="c3ref/column_count.html">sqlite3_column_count()</a>
function returns the number of columns in
the results set.  sqlite3_column_count() can be called at any time after

<a href="c3ref/prepare.html">sqlite3_prepare_v2()</a>.  
<a href="c3ref/data_count.html">sqlite3_data_count()</a> works similarly to

<a href="c3ref/column_count.html">sqlite3_column_count()</a> except that it only works following 
<a href="c3ref/step.html">sqlite3_step()</a>.
If the previous call to 
<a href="c3ref/step.html">sqlite3_step()</a> returned SQLITE_DONE or an error code,
then 
<a href="c3ref/data_count.html">sqlite3_data_count()</a> will return 0 whereas 
<a href="c3ref/column_count.html">sqlite3_column_count()</a> will
continue to return the number of columns in the result set.
</p>

<p>Returned data is examined using the other 

<a href="c3ref/column_blob.html">sqlite3_column_***()</a> functions, 
all of which take a column number as their second parameter. Columns are
zero-indexed from left to right. Note that this is different to parameters,
which are indexed starting at one.
</p>

<p>
The 
<a href="c3ref/column_blob.html">sqlite3_column_type()</a> function returns the
datatype for the value in the Nth column.  The return value is one
of these:
</p>

<blockquote><pre>
   #define SQLITE_INTEGER  1
   #define SQLITE_FLOAT    2
   #define SQLITE_TEXT     3
   #define SQLITE_BLOB     4
   #define SQLITE_NULL     5
</pre></blockquote>

<p>
The sqlite3_column_decltype() routine returns text which is the
declared type of the column in the CREATE TABLE statement.  For an
expression, the return type is an empty string.  sqlite3_column_name()
returns the name of the Nth column.  sqlite3_column_bytes() returns
the number of bytes in a column that has type BLOB or the number of bytes
in a TEXT string with UTF-8 encoding.  sqlite3_column_bytes16() returns
the same value for BLOBs but for TEXT strings returns the number of bytes
in a UTF-16 encoding.
sqlite3_column_blob() return BLOB data.  
sqlite3_column_text() return TEXT data as UTF-8.
sqlite3_column_text16() return TEXT data as UTF-16.
sqlite3_column_int() return INTEGER data in the host machines native
integer format.
sqlite3_column_int64() returns 64-bit INTEGER data.
Finally, sqlite3_column_double() return floating point data.
</p>

<p>
It is not necessary to retrieve data in the format specify by
sqlite3_column_type().  If a different format is requested, the data
is converted automatically.
</p>

<p>
Data format conversions can invalidate the pointer returned by
prior calls to sqlite3_column_blob(), sqlite3_column_text(), and/or
sqlite3_column_text16().  Pointers might be invalided in the following
cases:
</p>
<ul>
<li><p>
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.
</p></li>
<li><p>
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.
</p></li>
<li><p>
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.
</p></li>
</ul>
<p>
Note that 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 points to will have been modified.  Other kinds
of conversion are done in place when it is possible, but sometime it is
not possible and in those cases prior pointers are invalidated.  
</p>

<p>
The safest and easiest to remember policy is this: assume that any
result from
<ul>
<li>sqlite3_column_blob(),</li>
<li>sqlite3_column_text(), or</li>
<li>sqlite3_column_text16()</li>
</ul>
is invalided by subsequent calls to 
<ul>
<li>sqlite3_column_bytes(),</li>
<li>sqlite3_column_bytes16(),</li>
<li>sqlite3_column_text(), or</li>
<li>sqlite3_column_text16().</li>
</ul>
This means that you should always call sqlite3_column_bytes() or
sqlite3_column_bytes16() <u>before</u> calling sqlite3_column_blob(),
sqlite3_column_text(), or sqlite3_column_text16().
</p>

<h4>2.3 User-defined functions</h4>

<p>
User defined functions can be created using the following routine:
</p>

<blockquote><pre>
   typedef struct sqlite3_value sqlite3_value;
   int sqlite3_create_function(
     sqlite3 *,
     const char *zFunctionName,
     int nArg,
     int eTextRep,
     void*,
     void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
     void (*xStep)(sqlite3_context*,int,sqlite3_value**),
     void (*xFinal)(sqlite3_context*)
   );
   int sqlite3_create_function16(
     sqlite3*,
     const void *zFunctionName,
     int nArg,
     int eTextRep,
     void*,
     void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
     void (*xStep)(sqlite3_context*,int,sqlite3_value**),
     void (*xFinal)(sqlite3_context*)
   );
   #define SQLITE_UTF8     1
   #define SQLITE_UTF16    2
   #define SQLITE_UTF16BE  3
   #define SQLITE_UTF16LE  4
   #define SQLITE_ANY      5
</pre></blockquote>

<p>
The nArg parameter specifies the number of arguments to the function.
A value of 0 indicates that any number of arguments is allowed.  The
eTextRep parameter specifies what representation text values are expected
to be in for arguments to this function.  The value of this parameter should
be one of the parameters defined above.  SQLite version 3 allows multiple
implementations of the same function using different text representations.
The database engine chooses the function that minimization the number
of text conversions required.
</p>

<p>
Normal functions specify only xFunc and leave xStep and xFinal set to NULL.
Aggregate functions specify xStep and xFinal and leave xFunc set to NULL.
There is no separate sqlite3_create_aggregate() API.
</p>

<p>
The function name is specified in UTF-8.  A separate sqlite3_create_function16()
API works the same as sqlite_create_function()
except that the function name is specified in UTF-16 host byte order.
</p>

<p>
Notice that the parameters to functions are now pointers to sqlite3_value
structures instead of pointers to strings as in SQLite version 2.X.
The following routines are used to extract useful information from these
"values":
</p>

<blockquote><pre>
   const void *sqlite3_value_blob(sqlite3_value*);
   int sqlite3_value_bytes(sqlite3_value*);
   int sqlite3_value_bytes16(sqlite3_value*);
   double sqlite3_value_double(sqlite3_value*);
   int sqlite3_value_int(sqlite3_value*);
   long long int sqlite3_value_int64(sqlite3_value*);
   const unsigned char *sqlite3_value_text(sqlite3_value*);
   const void *sqlite3_value_text16(sqlite3_value*);
   int sqlite3_value_type(sqlite3_value*);
</pre></blockquote>

<p>
Function implementations use the following APIs to acquire context and
to report results:
</p>

<blockquote><pre>
   void *sqlite3_aggregate_context(sqlite3_context*, int nbyte);
   void *sqlite3_user_data(sqlite3_context*);
   void sqlite3_result_blob(sqlite3_context*, const void*, int n, void(*)(void*));
   void sqlite3_result_double(sqlite3_context*, double);
   void sqlite3_result_error(sqlite3_context*, const char*, int);
   void sqlite3_result_error16(sqlite3_context*, const void*, int);
   void sqlite3_result_int(sqlite3_context*, int);
   void sqlite3_result_int64(sqlite3_context*, long long int);
   void sqlite3_result_null(sqlite3_context*);
   void sqlite3_result_text(sqlite3_context*, const char*, int n, void(*)(void*));
   void sqlite3_result_text16(sqlite3_context*, const void*, int n, void(*)(void*));
   void sqlite3_result_value(sqlite3_context*, sqlite3_value*);
   void *sqlite3_get_auxdata(sqlite3_context*, int);
   void sqlite3_set_auxdata(sqlite3_context*, int, void*, void (*)(void*));
</pre></blockquote>

<h4>2.4 User-defined collating sequences</h4>

<p>
The following routines are used to implement user-defined
collating sequences:
</p>

<blockquote><pre>
   sqlite3_create_collation(sqlite3*, const char *zName, int eTextRep, void*,
      int(*xCompare)(void*,int,const void*,int,const void*));
   sqlite3_create_collation16(sqlite3*, const void *zName, int eTextRep, void*,
      int(*xCompare)(void*,int,const void*,int,const void*));
   sqlite3_collation_needed(sqlite3*, void*, 
      void(*)(void*,sqlite3*,int eTextRep,const char*));
   sqlite3_collation_needed16(sqlite3*, void*,
      void(*)(void*,sqlite3*,int eTextRep,const void*));
</pre></blockquote>

<p>
The sqlite3_create_collation() function specifies a collating sequence name
and a comparison function to implement that collating sequence.  The
comparison function is only used for comparing text values.  The eTextRep
parameter is one of SQLITE_UTF8, SQLITE_UTF16LE, SQLITE_UTF16BE, or
SQLITE_ANY to specify which text representation the comparison function works
with.  Separate comparison functions can exist for the same collating
sequence for each of the UTF-8, UTF-16LE and UTF-16BE text representations.
The sqlite3_create_collation16() works like sqlite3_create_collation() except
that the collation name is specified in UTF-16 host byte order instead of
in UTF-8.
</p>

<p>
The sqlite3_collation_needed() routine registers a callback which the
database engine will invoke if it encounters an unknown collating sequence.
The callback can lookup an appropriate comparison function and invoke
sqlite_3_create_collation() as needed.  The fourth parameter to the callback
is the name of the collating sequence in UTF-8.  For sqlite3_collation_need16()
the callback sends the collating sequence name in UTF-16 host byte order.
</p>

<hr><small<i>
This page last modified 2007/12/19 13:42:44 UTC
</i></small></div></body></html>