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<title>PTypes: string: typecasts</title>
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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>:
<a href="string.html">string</a>: Typecasts </p>
<blockquote>
<pre class="lang">#include <ptypes.h>
class string {
operator (const char*)() const;
}</pre>
</blockquote>
<p>A string object can be assigned to a variable or passed as an actual parameter
of type <span class="lang">const char*</span> implicitly (by default). Such assignments
should be used carefully, since the library does not keep track of whether a char
pointer refers to the given string buffer. To make sure that a char pointer refers
to a valid string buffer, always make the scope of a char pointer variable smaller
than or equal to the scope of a string object. In most cases passing a string
object to a system or API call is safe (see examples below). This typecast operator
does not perform any actions and simply returns a pointer to the string buffer.</p>
<p>The value of the char pointer is guaranteed to be non-NULL. Even if the string
is empty, the char pointer will refer to a null-symbol.</p>
<p>A string buffer can not be modified through a constant char pointer. If you
want to modify the string buffer through a char pointer, use <span class="lang">unique(string&)</span>
function instead. This function always returns a reference to a unique string
buffer (i.e. when the reference count is 1).</p>
<p><b>Compatibility note</b>: MSVC and GCC may treat type casts in different ways
when passing a string object to a function that takes (...) parameters, e.g. <span class="lang">printf()</span>
or <span class="lang">outstm::putf()</span>. You should explicitly instruct the
compiler to cast the string object to <span class="lang">(const char*)</span>
to avoid this problem. PTypes provides a shorter typedef <span class="lang">pconst</span>
for this.</p>
<p><b>Examples</b></p>
<blockquote>
<pre>
void assignment_example()
{
string s = "abcdef";
const char* p = s;
<span class="comment">// do string manipulation here...</span>
}
void function_call_example()
{
string s = "abcdef";
puts(s);
printf("%s\n", pconst(s));
}
</pre>
</blockquote>
<p class="seealso">See also: <a href="string.constructors.html">Constructors/destructors</a>,
<a href="string.operators.html">Operators</a>, <a href="string.manipulation.html">Manipulation</a>,
<a href="string.conversion.html">Conversion</a></p>
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