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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Hyperlinked ECMA C# Language Specification</title><meta name="author" content="Jon Jagger" /><link rel="stylesheet" href="ecma334.css"></link></head><body><div align="right"><em><a href="http://www.jaggersoft.com">Jon Jagger</a></em></div><div align="right"><a href="mailto:jon@jaggersoft.com">jon@jaggersoft.com</a></div><form method="get" action="http://search.atomz.com/search/"><input size="30" name="sp-q"></input><input type="submit" value="Search C# Spec"></input><input type="hidden" name="sp-a" value="sp10024177"></input><input type="hidden" name="sp-f" value="ISO-8859-1"></input></form><a href="toc.htm">Table of Contents</a> <a href="1.htm">1</a> <a href="2.htm">2</a> <a href="3.htm">3</a> <a href="4.htm">4</a> <a href="5.htm">5</a> <a href="6.htm">6</a> <a href="7.htm">7</a> <a href="8.htm">8</a> <a href="9.htm">9</a> <a href="10.htm">10</a> <a href="11.htm">11</a> <a href="12.htm">12</a> <a href="13.htm">13</a> <a href="14.htm">14</a> <a href="15.htm">15</a> <a href="16.htm">16</a> <a href="17.htm">17</a> <a href="18.htm">18</a> <a href="19.htm">19</a> <a href="20.htm">20</a> <a href="21.htm">21</a> <a href="22.htm">22</a> <a href="23.htm">23</a> <a href="24.htm">24</a> <a href="25.htm">25</a> <a href="notes.htm">Notes</a> <a href="HyperlinkedCSharpECMA.zip">Download</a><span class="ruler"></span><span class="heading">ECMA-334 C# Language Specification</span><span class="navigate"><a href="25.7.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="25.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="24.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="25.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="25.htm">25</a></span><span class="clause-title-previous"> Unsafe code</span></span><span class="clause-depth"><a href="25.7.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="25.8.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">25.8</span><span class="clause-title"> Dynamic memory allocation</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>Except for the stackalloc operator, C# provides no predefined constructs for managing non-garbage collected memory.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>Such services are typically provided by supporting class libraries or imported directly from the underlying operating system.</span> <span class="example">[Example: For example, the Memory class below illustrates how the heap functions of an underlying operating system might be accessed from C#: <pre class="code-example">
using System;
using System.Runtime.InteropServices;
public unsafe class Memory
{
// Handle for the process heap. This handle is used in all calls to
the
// HeapXXX APIs in the methods below.
static int ph = GetProcessHeap();
// Private instance constructor to prevent instantiation.
private Memory() {}
// Allocates a memory block of the given size. The allocated memory is
// automatically initialized to zero.
public static void* Alloc(int size) {
void* result = HeapAlloc(ph, HEAP_ZERO_MEMORY, size);
if (result == null) throw new OutOfMemoryException();
return result;
}
// Copies count bytes from src to dst. The source and destination
// blocks are permitted to overlap.
public static void Copy(void* src, void* dst, int count) {
byte* ps = (byte*)src;
byte* pd = (byte*)dst;
if (ps > pd) {
for (; count != 0; count--) *pd++ = *ps++;
}
else if (ps < pd) {
for (ps += count, pd += count; count != 0; count--) *--pd = *--
ps;
}
}
// Frees a memory block.
public static void Free(void* block) {
if (!HeapFree(ph, 0, block)) throw new InvalidOperationException();
}
// Re-allocates a memory block. If the reallocation request is for a
// larger size, the additional region of memory is automatically
// initialized to zero.
public static void* ReAlloc(void* block, int size) {
void* result = HeapReAlloc(ph, HEAP_ZERO_MEMORY, block, size);
if (result == null) throw new OutOfMemoryException();
return result;
}
// Returns the size of a memory block.
public static int SizeOf(void* block) {
int result = HeapSize(ph, 0, block);
if (result == -1) throw new InvalidOperationException();
return result;
}
// Heap API flags
const int HEAP_ZERO_MEMORY = 0x00000008;
// Heap API functions
[DllImport("kernel32")]
static extern int GetProcessHeap();
[DllImport("kernel32")]
static extern void* HeapAlloc(int hHeap, int flags, int size);
[DllImport("kernel32")]
static extern bool HeapFree(int hHeap, int flags, void* block);
[DllImport("kernel32")]
static extern void* HeapReAlloc(int hHeap, int flags,
void* block, int size);
[DllImport("kernel32")]
static extern int HeapSize(int hHeap, int flags, void* block);
}
</pre></span></span><span class="paragraph"><span class="example">An example that uses the Memory class is given below: <pre class="code-example">
class Test
{
static void Main() {
unsafe {
byte* buffer = (byte*)Memory.Alloc(256);
for (int i = 0; i < 256; i++) buffer[i] = (byte)i;
byte[] array = new byte[256];
fixed (byte* p = array) Memory.Copy(buffer, p, 256);
Memory.Free(buffer);
for (int i = 0; i < 256; i++) Console.WriteLine(array[i]);
}
}
}
</pre></span></span><span class="paragraph"><span class="example">The example allocates 256 bytes of memory through Memory.Alloc and initializes the memory block with values increasing from 0 to 255. It then allocates a 256-element <span class="keyword">byte</span> array and uses Memory.Copy to copy the contents of the memory block into the <span class="keyword">byte</span> array. Finally, the memory block is freed using Memory.Free and the contents of the <span class="keyword">byte</span> array are output on the console. end example]</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>End of conditionally normative text.</span> </span><span class="ruler"></span><table><tr><td><table align="left" bgcolor="navy"><tr bgcolor="navy"><td><font face="Arial,sans-serif" size="6" color="yellow"><strong>{ JSL }</strong></font></td></tr></table></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Jagger Software Ltd</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Company # 4070126</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>VAT # 762 5213 42</strong></font></td></tr></table><img src="valid-html401.png" align="left" height="31" width="88" alt="Valid HTML 4.01" /><img src="vcss.gif" align="left" height="31" width="88" alt="Valid CSS" /></body></html>⌨️ 快捷键说明
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