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<H1> B.3 Interfacing with C</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
<A NAME="I6348"></A><A NAME="I6349"></A>The facilities relevant to interfacing
with the C language are the package Interfaces.C and its children; <S>and
</S>support for the Import, Export, and Convention pragmas with <I>convention</I>_<FONT FACE="Arial, Helvetica">identifier</FONT>
C<U>; and support for the Convention pragma with <I>convention</I>_<FONT FACE="Arial, Helvetica">identifier</FONT>
C_Pass_By_Copy</U>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> The package Interfaces.C contains the basic types,
constants and subprograms that allow an Ada program to pass scalars and
strings to C functions. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The library package
Interfaces.C has the following declaration: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> Interfaces.C <B>is</B><A NAME="I6350"></A><A NAME="I6351"></A><A NAME="I6352"></A><BR>
<B>pragma</B> Pure(C);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Declarations based on C's <limits.h></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Examples"><TT> <A NAME="I6353"></A>CHAR_BIT : <B>constant</B> := <I>implementation-defined</I>; <I>-- typically 8</I><BR>
<A NAME="I6354"></A>SCHAR_MIN : <B>constant</B> := <I>implementation-defined</I>; <I>-- typically -128</I><BR>
<A NAME="I6355"></A>SCHAR_MAX : <B>constant</B> := <I>implementation-defined</I>; <I>-- typically 127</I><BR>
<A NAME="I6356"></A>UCHAR_MAX : <B>constant</B> := <I>implementation-defined</I>; <I>-- typically 255</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Signed and Unsigned Integers</I><BR>
<B>type</B> <A NAME="I6357"></A><A NAME="I6358"></A>int <B>is</B> <B>range</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I6359"></A><A NAME="I6360"></A>short <B>is</B> <B>range</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I6361"></A><A NAME="I6362"></A>long <B>is</B> <B>range</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6363"></A><A NAME="I6364"></A>signed_char <B>is</B> <B>range</B> SCHAR_MIN .. SCHAR_MAX;<BR>
<B>for</B> signed_char'Size <B>use</B> CHAR_BIT;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6365"></A><A NAME="I6366"></A>unsigned <B>is</B> <B>mod</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I6367"></A><A NAME="I6368"></A>unsigned_short <B>is</B> <B>mod</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I6369"></A><A NAME="I6370"></A>unsigned_long <B>is</B> <B>mod</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6371"></A><A NAME="I6372"></A>unsigned_char <B>is</B> <B>mod</B> (UCHAR_MAX+1);<BR>
<B>for</B> unsigned_char'Size <B>use</B> CHAR_BIT;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Examples"><TT> <B>subtype</B> <A NAME="I6373"></A><A NAME="I6374"></A>plain_char <B>is</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6375"></A><A NAME="I6376"></A>ptrdiff_t <B>is</B> <B>range</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6377"></A><A NAME="I6378"></A>size_t <B>is</B> <B>mod</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Floating Point</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6379"></A><A NAME="I6380"></A>C_float <B>is</B> <B>digits</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6381"></A><A NAME="I6382"></A>double <B>is</B> <B>digits</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6383"></A><A NAME="I6384"></A>long_double <B>is</B> <B>digits</B> <I>implementation-defined</I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Characters and Strings </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6385"></A><A NAME="I6386"></A>char <B>is</B> <I><implementation-defined character type></I>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20/1</FONT></DIV>
<DIV Class="Examples"><TT>{<I><A HREF="defect1.html#8652/0060">8652/0060</A></I>}
<BR>
<A NAME="I6387"></A>nul : <B>constant</B> char := <U><I>implementation-defined</I></U><S>char'First</S>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6388"></A><A NAME="I6389"></A>To_C (Item : <B>in</B> Character) <B>return</B> char;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6390"></A><A NAME="I6391"></A>To_Ada (Item : <B>in</B> char) <B>return</B> Character;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6392"></A><A NAME="I6393"></A>char_array <B>is</B> <B>array</B> (size_t <B>range</B> <>) <B>of</B> <B>aliased</B> char;<BR>
<B>pragma</B> Pack(char_array);<BR>
<B>for</B> char_array'Component_Size <B>use</B> CHAR_BIT;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6394"></A><A NAME="I6395"></A>Is_Nul_Terminated (Item : <B>in</B> char_array) <B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>25</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6396"></A><A NAME="I6397"></A>To_C (Item : <B>in</B> String;<BR>
Append_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> char_array;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>26</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6398"></A><A NAME="I6399"></A>To_Ada (Item : <B>in</B> char_array;<BR>
Trim_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> String;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>27</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6400"></A><A NAME="I6401"></A>To_C (Item : <B>in</B> String;<BR>
Target : <B>out</B> char_array;<BR>
Count : <B>out</B> size_t;<BR>
Append_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>28</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6402"></A><A NAME="I6403"></A>To_Ada (Item : <B>in</B> char_array;<BR>
Target : <B>out</B> String;<BR>
Count : <B>out</B> Natural;<BR>
Trim_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>29</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Wide Character and Wide String</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>30/1</FONT></DIV>
<DIV Class="Examples"><TT>{<I><A HREF="defect1.html#8652/0060">8652/0060</A></I>}
<BR>
<B>type</B> <A NAME="I6404"></A><A NAME="I6405"></A>wchar_t <B>is</B> <U><I><implementation-defined character type></I></U><S><I>implementation-defined</I></S>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>31/1</FONT></DIV>
<DIV Class="Examples"><TT>{<I><A HREF="defect1.html#8652/0060">8652/0060</A></I>}
<BR>
<A NAME="I6406"></A>wide_nul : <B>constant</B> wchar_t := <U><I>implementation-defined</I></U><S>wchar_t'First</S>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>32</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6407"></A><A NAME="I6408"></A>To_C (Item : <B>in</B> Wide_Character) <B>return</B> wchar_t;<BR>
<B>function</B> <A NAME="I6409"></A><A NAME="I6410"></A>To_Ada (Item : <B>in</B> wchar_t ) <B>return</B> Wide_Character;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>33</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I6411"></A><A NAME="I6412"></A>wchar_array <B>is</B> <B>array</B> (size_t <B>range</B> <>) <B>of</B> <B>aliased</B> wchar_t;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>34</FONT></DIV>
<DIV Class="Examples"><TT> <B>pragma</B> Pack(wchar_array);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>35</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6413"></A><A NAME="I6414"></A>Is_Nul_Terminated (Item : <B>in</B> wchar_array) <B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>36</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6415"></A><A NAME="I6416"></A>To_C (Item : <B>in</B> Wide_String;<BR>
Append_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> wchar_array;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>37</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6417"></A><A NAME="I6418"></A>To_Ada (Item : <B>in</B> wchar_array;<BR>
Trim_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> Wide_String;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>38</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6419"></A><A NAME="I6420"></A>To_C (Item : <B>in</B> Wide_String;<BR>
Target : <B>out</B> wchar_array;<BR>
Count : <B>out</B> size_t;<BR>
Append_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>39</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I6421"></A><A NAME="I6422"></A>To_Ada (Item : <B>in</B> wchar_array;<BR>
Target : <B>out</B> Wide_String;<BR>
Count : <B>out</B> Natural;<BR>
Trim_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>40</FONT></DIV>
<DIV Class="Examples"><TT> <A NAME="I6423"></A>Terminator_Error : <B>exception</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>41</FONT></DIV>
<DIV Class="Examples"><TT><B>end</B> Interfaces.C;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>41.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B><U>The
definitions of types and constants in Interfaces.C.</U></FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>42</FONT></DIV>
<DIV Class="Normal"> Each of the types declared in Interfaces.C is
C-compatible.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>43</FONT></DIV>
<DIV Class="Normal"> The types int, short, long, unsigned, ptrdiff_t,
size_t, double, char, and wchar_t correspond respectively to the C types
having the same names. The types signed_char, unsigned_short, unsigned_long,
unsigned_char, C_float, and long_double correspond respectively to the
C types signed char, unsigned short, unsigned long, unsigned char, float,
and long double.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>44</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.9em"> The type of the
subtype plain_char is either signed_char or unsigned_char, depending
on the C implementation. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>45</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> To_C (Item : <B>in</B> Character) <B>return</B> char;<BR>
<B>function</B> To_Ada (Item : <B>in</B> char ) <B>return</B> Character;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>46</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">The functions
To_C and To_Ada map between the Ada type Character and the C type char.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>46.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation Note: </B>{<I><A HREF="defect2.html#8652/0114">8652/0114</A></I>}
<U>The To_C and To_Ada functions map between corresponding characters,
not necessarily between characters with the same internal representation.
Corresponding characters are characters defined by the same enumeration
literal, if such exist; otherwise, the correspondence is unspecified.<A NAME="I6424"></A></U></FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>46.a.2/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><U>The following definition is
equivalent to the above summary:</U></FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>46.a.3/1</FONT></DIV>
<DIV Class="Annotations" Style="margin-bottom: 0.4em"><FONT SIZE=-1><U><TT>To_C
(Latin_1_Char) = char'Value(Character'Image(Latin_1_Char))</TT><BR>
provided that char'Value does not raise an exception; otherwise the result
is unspecified.</U></FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>46.a.4/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><U><TT>To_Ada (Native_C_Char)
= Character'Value(char'Image(Native_C_Char))</TT><BR>
provided that Character'Value does not raise an exception; otherwise
the result is unspecified.</U> </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>47</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> Is_Nul_Terminated (Item : <B>in</B> char_array) <B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>48</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">The result of
Is_Nul_Terminated is True if Item contains nul, and is False otherwise.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>49</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> To_C (Item : <B>in</B> String; Append_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> char_array;<BR>
<BR>
<B>function</B> To_Ada (Item : <B>in</B> char_array; Trim_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> String;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>50</FONT></DIV>
<DIV Class="CodeIndented">The result of To_C is a char_array value of
length Item'Length (if Append_Nul is False) or Item'Length+1 (if Append_Nul
is True). The lower bound is 0. For each component Item(I), the corresponding
component in the result is To_C applied to Item(I). The value nul is
appended if Append_Nul is True.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>51</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">The result of
To_Ada is a String whose length is Item'Length (if Trim_Nul is False)
or the length of the slice of Item preceding the first nul (if Trim_Nul
is True). The lower bound of the result is 1. If Trim_Nul is False, then
for each component Item(I) the corresponding component in the result
is To_Ada applied to Item(I). If Trim_Nul is True, then for each component
Item(I) before the first nul the corresponding component in the result
is To_Ada applied to Item(I). The function propagates Terminator_Error
if Trim_Nul is True and Item does not contain nul.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>52</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> To_C (Item : <B>in</B> String;<BR>
Target : <B>out</B> char_array;<BR>
Count : <B>out</B> size_t;<BR>
Append_Nul : <B>in</B> Boolean := True);<BR>
<BR>
<B>procedure</B> To_Ada (Item : <B>in</B> char_array;<BR>
Target : <B>out</B> String;<BR>
Count : <B>out</B> Natural;<BR>
Trim_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>53</FONT></DIV>
<DIV Class="CodeIndented">For procedure To_C, each element of Item is
converted (via the To_C function) to a char, which is assigned to the
corresponding element of Target. If Append_Nul is True, nul is then assigned
to the next element of Target. In either case, Count is set to the number
of Target elements assigned. <A NAME="I6425"></A>If Target is not long
enough, Constraint_Error is propagated.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>54</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">For procedure
To_Ada, each element of Item (if Trim_Nul is False) or each element of
Item preceding the first nul (if Trim_Nul is True) is converted (via
the To_Ada function) to a Character, which is assigned to the corresponding
element of Target. Count is set to the number of Target elements assigned.
<A NAME="I6426"></A>If Target is not long enough, Constraint_Error is
propagated. If Trim_Nul is True and Item does not contain nul, then Terminator_Error
is propagated.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>55</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> Is_Nul_Terminated (Item : <B>in</B> wchar_array) <B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>56</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">The result of
Is_Nul_Terminated is True if Item contains wide_nul, and is False otherwise.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>57</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> To_C (Item : <B>in</B> Wide_Character) <B>return</B> wchar_t;<BR>
<B>function</B> To_Ada (Item : <B>in</B> wchar_t ) <B>return</B> Wide_Character;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>58</FONT></DIV>
<DIV Class="CodeIndented" Style="margin-bottom: 0.9em">To_C and To_Ada
provide the mappings between the Ada and C wide character types.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>59</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> To_C (Item : <B>in</B> Wide_String;<BR>
Append_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> wchar_array;<BR>
<BR>
<B>function</B> To_Ada (Item : <B>in</B> wchar_array;<BR>
Trim_Nul : <B>in</B> Boolean := True)<BR>
<B>return</B> Wide_String;<BR>
<BR>
<B>procedure</B> To_C (Item : <B>in</B> Wide_String;<BR>
Target : <B>out</B> wchar_array;<BR>
Count : <B>out</B> size_t;<BR>
Append_Nul : <B>in</B> Boolean := True);<BR>
<BR>
<B>procedure</B> To_Ada (Item : <B>in</B> wchar_array;<BR>
Target : <B>out</B> Wide_String;<BR>
Count : <B>out</B> Natural;<BR>
Trim_Nul : <B>in</B> Boolean := True);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60</FONT></DIV>
<DIV Class="CodeIndented">The To_C and To_Ada subprograms that convert
between Wide_String and wchar_array have analogous effects to the To_C
and To_Ada subprograms that convert between String and char_array, except
that wide_nul is used instead of nul. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The Interfaces.C
package provides an implementation-defined character type, char, designed
to model the C run-time character set, and mappings between the types
char and Character.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.b</FONT></DIV>
<DIV Class="Annotations" Style="margin-bottom: 0.4em"><FONT SIZE=-1>One
application of the C interface package is to compose a C string and pass
it to a C function. One way to do this is for the programmer to declare
an object that will hold the C array, and then pass this array to the
C function. This is realized via the type char_array: </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.c</FONT></DIV>
<DIV Class="SmallExamples"><TT><B>type</B> char_array <B>is</B> <B>array</B> (size_t <B>range</B> <>) of Char;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The programmer can declare an
Ada String, convert it to a char_array, and pass the char_array as actual
parameter to the C function that is expecting a char *.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.e</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>An alternative approach is for
the programmer to obtain a C char pointer from an Ada String (or from
a char_array) by invoking an allocation function. The package Interfaces.C.Strings
(see below) supplies the needed facilities, including a private type
chars_ptr that corresponds to C's char *, and two allocation functions.
To avoid storage leakage, a Free procedure releases the storage that
was allocated by one of these allocate functions.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.f</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>It is typical for a C function
that deals with strings to adopt the convention that the string is delimited
by a nul char. The C interface packages support this convention. A constant
nul of type Char is declared, and the function Value(Chars_Ptr) in Interfaces.C.Strings
returns a char_array up to and including the first nul in the array that
the chars_ptr points to. The Allocate_Chars function allocates an array
that is nul terminated.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.g</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Some C functions that deal with
strings take an explicit length as a parameter, thus allowing strings
to be passed that contain nul as a data element. Other C functions take
an explicit length that is an upper bound: the prefix of the string up
to the char before nul, or the prefix of the given length, is used by
the function, whichever is shorter. The C Interface packages support
calling such functions. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
<U>A Convention pragma with <I>convention</I>_<FONT FACE="Arial, Helvetica">identifier</FONT>
C_Pass_By_Copy shall only be applied to a type.</U></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.2/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
<U>The eligibility rules in <A HREF="AA-B-1.html">B.1</A> do not apply
to convention C_Pass_By_Copy. Instead, a type T is eligible for convention
C_Pass_By_Copy if T is a record type that has no discriminants and that
only has components with statically constrained subtypes, and each component
is C-compatible.</U></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>60.3/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
<U>If a type is C_Pass_By_Copy-compatible then it is also C-compatible.</U></DIV>
<H4 ALIGN=CENTER>Implementation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>61/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
An implementation shall support pragma Convention with a C <I>convention</I>_<FONT FACE="Arial, Helvetica">identifier</FONT>
for a C-eligible type (see <A HREF="AA-B-1.html">B.1</A>)<U>. An implementation
shall support pragma Convention with a C_Pass_By_Copy <I>convention</I>_<FONT FACE="Arial, Helvetica">identifier</FONT>
for a C_Pass_By_Copy-eligible type.</U> </DIV>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>62</FONT></DIV>
<DIV Class="Normal"> An implementation may provide additional declarations
in the C interface packages. </DIV>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>62.1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0060">8652/0060</A></I>}
<U>The constants nul and wide_nul should have a representation of zero.</U></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>63</FONT></DIV>
<DIV Class="Normal"> An implementation should support the following
interface correspondences between Ada and C. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>64</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada procedure corresponds to a void-returning C function.
</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>64.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The programmer
can also choose an Ada procedure when the C function returns an int that
is to be discarded.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>65</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada function corresponds to a non-void C function.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>66</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada <B>in</B> scalar parameter is passed as a scalar
argument to a C function.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>67</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada <B>in</B> parameter of an access-to-object type
with designated type T is passed as a t* argument to a C function, where
t is the C type corresponding to the Ada type T.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>68</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada <B>access</B> T parameter, or an Ada <B>out</B>
or <B>in out</B> parameter of an elementary type T, is passed as a t*
argument to a C function, where t is the C type corresponding to the
Ada type T. In the case of an elementary <B>out</B> or <B>in out</B>
parameter, a pointer to a temporary copy is used to preserve by-copy
semantics.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>68.1/1</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>{<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
<U>An Ada parameter of a C_Pass_By_Copy-compatible (record) type T, of
mode <B>in</B>, is passed as a t argument to a C function, where t is
the C struct corresponding to the Ada type T.</U></LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>69/1</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>{<I><A HREF="defect1.html#8652/0059">8652/0059</A></I>}
An Ada parameter of a record type T, of any mode, <U>other than an <B>in</B>
parameter of a C_Pass_By_Copy-compatible type,</U> is passed as a t*
argument to a C function, where t is the C struct corresponding to the
Ada type T.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>70</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada parameter of an array type with component type T,
of any mode, is passed as a t* argument to a C function, where t is the
C type corresponding to the Ada type T.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>71</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An Ada parameter of an access-to-subprogram type is passed
as a pointer to a C function whose prototype corresponds to the designated
subprogram's specification. </LI></UL>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>72</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>9 Values of type char_array
are not implicitly terminated with nul. If a char_array is to be passed
as a parameter to an imported C function requiring nul termination, it
is the programmer's responsibility to obtain this effect.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>73</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>10 To obtain the effect of
C's sizeof(item_type), where Item_Type is the corresponding Ada type,
evaluate the expression: size_t(Item_Type'Size/CHAR_BIT).</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>74</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>11 There is no explicit support
for C's union types. Unchecked conversions can be used to obtain the
effect of C unions.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>75</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>12 A C function that takes
a variable number of arguments can correspond to several Ada subprograms,
taking various specific numbers and types of parameters. </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>76</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Example of using
the Interfaces.C package:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>77</FONT></DIV>
<DIV Class="Examples"><TT><I>--Calling the C Library Function strcpy</I><BR>
<B>with</B> Interfaces.C;<BR>
<B>procedure</B> Test <B>is</B><BR>
<B>package</B> C <B>renames</B> Interfaces.C;<BR>
<B>use</B> <B>type</B> C.char_array;<BR>
<I>-- Call <string.h>strcpy:</I><BR>
<I>-- C definition of strcpy: char *strcpy(char *s1, const char *s2);</I><BR>
<I>-- This function copies the string pointed to by s2 (including the terminating null character)</I><BR>
<I>-- into the array pointed to by s1. If copying takes place between objects that overlap, </I><BR>
<I>-- the behavior is undefined. The strcpy function returns the value of s1.</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>78</FONT></DIV>
<DIV Class="Examples"><TT> <I>-- Note: since the C function's return value is of no interest, the Ada interface is a procedure</I><BR>
<B>procedure</B> Strcpy (Target : <B>out</B> C.char_array;<BR>
Source : <B>in</B> C.char_array);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>79</FONT></DIV>
<DIV Class="Examples"><TT> <B>pragma</B> Import(C, Strcpy, "strcpy");</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>80</FONT></DIV>
<DIV Class="Examples"><TT> Chars1 : C.char_array(1..20);<BR>
Chars2 : C.char_array(1..20);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>81</FONT></DIV>
<DIV Class="Examples"><TT><B>begin</B><BR>
Chars2(1..6) := "qwert" & C.nul;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>82</FONT></DIV>
<DIV Class="Examples"><TT> Strcpy(Chars1, Chars2);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>83</FONT></DIV>
<DIV Class="Examples"><TT><I>-- Now Chars1(1..6) = "qwert" & C.Nul</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>84</FONT></DIV>
<DIV Class="Examples"><TT><B>end</B> Test;</TT></DIV>
<HR>
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