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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="14.5.10.1.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.5.10.3.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="13.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.htm">14</a></span><span class="clause-title-previous"> Expressions</span></span><span class="clause-depth"><a href="14.4.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.6.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.5.htm">14.5</a></span><span class="clause-title-previous"> Primary expressions</span></span><span class="clause-depth"><a href="14.5.9.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.5.11.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.5.10.htm">14.5.10</a></span><span class="clause-title-previous"> The new operator</span></span><span class="clause-depth"><a href="14.5.10.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.5.10.3.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.5.10.2</span><span class="clause-title"> Array creation expressions</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>An <span class="non-terminal"><a href="14.5.10.2.htm#array-creation-expression">array-creation-expression</a></span> is used to create a new instance of an <span class="non-terminal"><a href="19.1.htm#array-type">array-type</a></span>.</span> <span class="grammar-production"><span class="name"><a name="array-creation-expression"></a>array-creation-expression</span> : <span class="rhs"><span class="keyword">new</span> <span class="non-terminal"><a href="19.1.htm#non-array-type">non-array-type</a></span> <span class="terminal">[</span> <span class="non-terminal"><a href="14.5.6.htm#expression-list">expression-list</a></span> <span class="terminal">]</span> <span class="non-terminal"><a href="19.1.htm#rank-specifiers">rank-specifiers</a></span><sub>opt</sub> <span class="non-terminal"><a href="19.6.htm#array-initializer">array-initializer</a></span><sub>opt</sub> </span><span class="rhs"><span class="keyword">new</span> <span class="non-terminal"><a href="19.1.htm#array-type">array-type</a></span> <span class="non-terminal"><a href="19.6.htm#array-initializer">array-initializer</a></span> </span></span></span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>An array creation expression of the first form allocates an array instance of the type that results from deleting each of the individual expressions from the expression list.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>For example, the array creation expression new int[10,20] produces an array instance of type int[,], and the array creation expression new int[10][,] produces an array of type int[][,].</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>Each expression in the expression list must be of type <span class="keyword">int</span>, <span class="keyword">uint</span>, <span class="keyword">long</span>, or <span class="keyword">ulong</span>, or of a type that can be implicitly converted to one or more of these types.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a>The value of each expression determines the length of the corresponding dimension in the newly allocated array instance.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P2S5"></a>Since the length of an array dimension must be nonnegative, it is a compile-time error to have a constant expression with a negative value, in the expression list.</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>Except in an unsafe context (<a href="25.1.htm">§25.1</a>), the layout of arrays is unspecified.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>If an array creation expression of the first form includes an array initializer, each expression in the expression list must be a constant and the rank and dimension lengths specified by the expression list must match those of the array initializer.</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>In an array creation expression of the second form, the rank of the specified array type must match that of the array initializer.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>The individual dimension lengths are inferred from the number of elements in each of the corresponding nesting levels of the array initializer.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>Thus, the expression <pre class="code-example">
new int[,] {{0, 1}, {2, 3}, {4, 5}}
</pre>exactly corresponds to <pre class="code-example">
new int[3, 2] {{0, 1}, {2, 3}, {4, 5}}
</pre></span></span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>Array initializers are described further in <a href="19.6.htm">§19.6</a>.</span> </span><span class="locator">
Paragraph 7</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P7S1"></a>The result of evaluating an array creation expression is classified as a value, namely a reference to the newly allocated array instance.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P7S2"></a>The run-time processing of an array creation expression consists of the following steps: </span><ul><li><span class="sentence"><span class="sentence-number">3</span> <a name="P7S3"></a> The dimension length expressions of the <span class="non-terminal"><a href="14.5.6.htm#expression-list">expression-list</a></span> are evaluated in order, from left to right.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P7S4"></a>Following evaluation of each expression, an implicit conversion (<a href="13.1.htm">§13.1</a>) to one of the following types is performed: <span class="keyword">int</span>, <span class="keyword">uint</span>, <span class="keyword">long</span>, <span class="keyword">ulong</span>.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P7S5"></a>The first type in this list for which an implicit conversion exists is chosen.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P7S6"></a>If evaluation of an expression or the subsequent implicit conversion causes an exception, then no further expressions are evaluated and no further steps are executed.</span> </li><li><span class="sentence"><span class="sentence-number">7</span> <a name="P7S7"></a> The computed values for the dimension lengths are validated, as follows: If one or more of the values are less than zero, a System.OverflowException is thrown and no further steps are executed.</span> </li><li><span class="sentence"><span class="sentence-number">8</span> <a name="P7S8"></a> An array instance with the given dimension lengths is allocated.</span> <span class="sentence"><span class="sentence-number">9</span> <a name="P7S9"></a>If there is not enough memory available to allocate the new instance, a System.OutOfMemoryException is thrown and no further steps are executed.</span> </li><li><span class="sentence"><span class="sentence-number">10</span> <a name="P7S10"></a> All elements of the new array instance are initialized to their default values (<a href="12.2.htm">§12.2</a>).</span> </li><li><span class="sentence"><span class="sentence-number">11</span> <a name="P7S11"></a> If the array creation expression contains an array initializer, then each expression in the array initializer is evaluated and assigned to its corresponding array element.</span> <span class="sentence"><span class="sentence-number">12</span> <a name="P7S12"></a>The evaluations and assignments are performed in the order the expressions are written in the array initializer-in other words, elements are initialized in increasing index order, with the rightmost dimension increasing first.</span> <span class="sentence"><span class="sentence-number">13</span> <a name="P7S13"></a>If evaluation of a given expression or the subsequent assignment to the corresponding array element causes an exception, then no further elements are initialized (and the remaining elements will thus have their default values).</span> </li></ul></span><span class="locator">
Paragraph 8</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P8S1"></a>An array creation expression permits instantiation of an array with elements of an array type, but the elements of such an array must be manually initialized.</span> <span class="example">[Example: For example, the statement <pre class="code-example">
int[][] a = new int[100][];
</pre>creates a single-dimensional array with 100 elements of type int[]. The initial value of each element is null. end example]</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P8S2"></a>It is not possible for the same array creation expression to also instantiate the sub-arrays, and the statement <pre class="code-example">
int[][] a = new int[100][5]; // Error
</pre>results in a compile-time error.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P8S3"></a>Instantiation of the sub-arrays must instead be performed manually, as in <pre class="code-example">
int[][] a = new int[100][];
for (int i = 0; i < 100; i++) a[i] = new int[5];
</pre></span></span><span class="locator">
Paragraph 9</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P9S1"></a>When an array of arrays has a "rectangular" shape, that is when the sub-arrays are all of the same length, it is more efficient to use a multi-dimensional array.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P9S2"></a>In the example above, instantiation of the array of arrays creates 101 objects-one outer array and 100 sub-arrays.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P9S3"></a>In contrast, <pre class="code-example">
int[,] = new int[100, 5];
</pre>creates only a single object, a two-dimensional array, and accomplishes the allocation in a single statement.</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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