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Overview
Comment:Added explanation and examples for %Q format specifier. (CVS 623)
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SHA1:633ce4dd252ac351b04bdb7bed2d5374ee9a3f12
User & Date: chw 2002-06-16 04:57:32
Context
2002-06-16
18:21
Expose an additional internal API routine (sqliteInitCallback()) for use by private code. (CVS 624) check-in: cd74495f user: drh tags: trunk
04:57
Added explanation and examples for %Q format specifier. (CVS 623) check-in: 633ce4dd user: chw tags: trunk
04:56
Added printf-4.(2-4) test cases to test new %Q format specifier. (CVS 622) check-in: 7d5fc35b user: chw tags: trunk
Changes
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Changes to www/c_interface.tcl.

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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: c_interface.tcl,v 1.29 2002/05/15 23:26:23 drh Exp $}

puts {<html>
<head>
  <title>The C language interface to the SQLite library</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
SQLite printf routines, there is never a danger of overflowing a
static buffer as there is with <b>sprintf()</b>.  The SQLite
printf routines automatically allocate (and later free)
as much memory as is 
necessary to hold the SQL statements generated.</p>

<p>The second advantage the SQLite printf routines have over
<b>sprintf()</b> is a new formatting option specifically designed
to support string literals in SQL.  Within the format string,
the %q formatting option works very much like %s in that it
reads a null-terminated string from the argument list and inserts
it into the result.  But %q translates the inserted string by
making two copies of every single-quote (') character in the
substituted string.  This has the effect of escaping the end-of-string
meaning of single-quote within a string literal.




</p>

<p>Consider an example.  Suppose you are trying to insert a string
value into a database table where the string value was obtained from
user input.  Suppose the string to be inserted is stored in a variable
named zString.  The code to do the insertion might look like this:</p>

................................................................................
</pre></blockquote>

<p>Here the apostrophy has been escaped and the SQL statement is well-formed.
When generating SQL on-the-fly from data that might contain a
single-quote character ('), it is always a good idea to use the
SQLite printf routines and the %q formatting option instead of <b>sprintf</b>.
</p>























<h2>Adding New SQL Functions</h2>

<p>Beginning with version 2.4.0, SQLite allows the SQL language to be
extended with new functions implemented as C code.  The following interface
is used:
</p>



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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: c_interface.tcl,v 1.30 2002/06/16 04:57:32 chw Exp $}

puts {<html>
<head>
  <title>The C language interface to the SQLite library</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
SQLite printf routines, there is never a danger of overflowing a
static buffer as there is with <b>sprintf()</b>.  The SQLite
printf routines automatically allocate (and later free)
as much memory as is 
necessary to hold the SQL statements generated.</p>

<p>The second advantage the SQLite printf routines have over
<b>sprintf()</b> are two new formatting options specifically designed
to support string literals in SQL.  Within the format string,
the %q formatting option works very much like %s in that it
reads a null-terminated string from the argument list and inserts
it into the result.  But %q translates the inserted string by
making two copies of every single-quote (') character in the
substituted string.  This has the effect of escaping the end-of-string
meaning of single-quote within a string literal. The %Q formatting
option works similar; it translates the single-quotes like %q and
additionally encloses the resulting string in single-quotes.
If the argument for the %Q formatting options is a NULL pointer,
the resulting string is NULL without single quotes.
</p>

<p>Consider an example.  Suppose you are trying to insert a string
value into a database table where the string value was obtained from
user input.  Suppose the string to be inserted is stored in a variable
named zString.  The code to do the insertion might look like this:</p>

................................................................................
</pre></blockquote>

<p>Here the apostrophy has been escaped and the SQL statement is well-formed.
When generating SQL on-the-fly from data that might contain a
single-quote character ('), it is always a good idea to use the
SQLite printf routines and the %q formatting option instead of <b>sprintf</b>.
</p>

<p>If the %Q formatting option is used instead of %q, like this:</p>

<blockquote><pre>
sqlite_exec_printf(db,
  "INSERT INTO table1 VALUES(%Q)",
  0, 0, 0, zString);
</pre></blockquote>

<p>Then the generated SQL will look like the following:</p>

<blockquote><pre>
INSERT INTO table1 VALUES('Hi y''all')
</pre></blockquote>

<p>If the value of the zString variable is NULL, the generated SQL
will look like the following:</p>

<blockquote><pre>
INSERT INTO table1 VALUES(NULL)
</pre></blockquote>


<h2>Adding New SQL Functions</h2>

<p>Beginning with version 2.4.0, SQLite allows the SQL language to be
extended with new functions implemented as C code.  The following interface
is used:
</p>