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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="14.7.3.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.7.5.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="14.6.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.8.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.7.htm">14.7</a></span><span class="clause-title-previous"> Arithmetic operators</span></span><span class="clause-depth"><a href="14.7.3.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.7.5.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.7.4</span><span class="clause-title"> Addition operator</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>For an operation of the form x + y, binary operator overload resolution (<a href="14.2.4.htm">§14.2.4</a>) is applied to select a specific operator implementation.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>The operands are converted to the parameter types of the selected operator, and the type of the result is the return type of the operator.</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>The predefined addition operators are listed below.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>For numeric and enumeration types, the predefined addition operators compute the sum of the two operands.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a>When one or both operands are of type string, the predefined addition operators concatenate the string representation of the operands.</span> <ul><li><span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a> Integer addition: <pre class="code-example">
int operator +(int x, int y);
uint operator +(uint x, uint y);
long operator +(long x, long y);
ulong operator +(ulong x, ulong y);
</pre><span class="sentence"><span class="sentence-number">5</span> <a name="P2S5"></a>In a checked context, if the sum is outside the range of the result type, a System.OverflowException is thrown.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P2S6"></a>In an unchecked context, overflows are not reported and any significant high-order bits outside the range of the result type are discarded.</span> </span></li><li><span class="sentence"><span class="sentence-number">7</span> <a name="P2S7"></a> Floating-point addition: <pre class="code-example">
float operator +(float x, float y);
double operator +(double x, double y);
</pre><span class="sentence"><span class="sentence-number">8</span> <a name="P2S8"></a>The sum is computed according to the rules of IEEE 754 arithmetic.</span> <span class="sentence"><span class="sentence-number">9</span> <a name="P2S9"></a>The following table lists the results of all possible combinations of nonzero finite values, zeros, infinities, and NaN's.</span> <span class="sentence"><span class="sentence-number">10</span> <a name="P2S10"></a>In the table, x and y are nonzero finite values, and z is the result of x + y.</span> <span class="sentence"><span class="sentence-number">11</span> <a name="P2S11"></a>If x and y have the same magnitude but opposite signs, z is positive zero.</span> <span class="sentence"><span class="sentence-number">12</span> <a name="P2S12"></a>If x + y is too large to represent in the destination type, z is an infinity with the same sign as x + y.</span> <span class="sentence"><span class="sentence-number">13</span> <a name="P2S13"></a>If x + y is too small to represent in the destination type, z is a zero with the same sign as x + y.</span>
<table border="1">
<tr>
<th>+</th>
<th>y</th>
<th>+0</th>
<th>-0</th>
<th>+∞</th>
<th>-∞</th>
<th>NaN</th>
</tr>
<tr>
<th><b>x</th>
<td>z</td>
<td>x</td>
<td>x</td>
<td>+∞</td>
<td>-∞</td>
<td>NaN</td>
</tr>
<tr>
<th>+0</th>
<td>y</td>
<td>+0</td>
<td>+0</td>
<td>+∞</td>
<td>-∞</td>
<td>NaN</td>
</tr>
<tr>
<th>-0</th>
<td>y</td>
<td>+0</td>
<td>-0</td>
<td>+∞</td>
<td>-∞</td>
<td>NaN</td>
</tr>
<tr>
<th>+∞</th>
<td>+∞</td>
<td>+∞</td>
<td>+∞</td>
<td>+∞</td>
<td>NaN</td>
<td>NaN</td>
</tr>
<tr>
<th>-∞</th>
<td>-∞</td>
<td>-∞</td>
<td>-∞</td>
<td>NaN</td>
<td>-∞</td>
<td>NaN</td>
</tr>
<tr>
<th>NaN</th>
<td>NaN</td>
<td>NaN</td>
<td>NaN</td>
<td>NaN</td>
<td>NaN</td>
<td>NaN</td>
</tr>
</table>
</span></li><li><span class="sentence"><span class="sentence-number">14</span> <a name="P2S14"></a> Decimal addition: <pre class="code-example">
decimal operator +(decimal x, decimal y);
</pre><span class="sentence"><span class="sentence-number">15</span> <a name="P2S15"></a>If the resulting value is too large to represent in the <span class="keyword">decimal</span> format, a System.OverflowException is thrown.</span> <span class="sentence"><span class="sentence-number">16</span> <a name="P2S16"></a>The scale of the result, before any rounding, is the larger of the scales of the two operands.</span> <span class="sentence"><span class="sentence-number">17</span> <a name="P2S17"></a>Decimal addition is equivalent to using the addition operator of type System.Decimal.</span> </span></li><li><span class="sentence"><span class="sentence-number">18</span> <a name="P2S18"></a> Enumeration addition.</span> <span class="sentence"><span class="sentence-number">19</span> <a name="P2S19"></a>Every enumeration type implicitly provides the following predefined operators, where E is the enum type, and U is the underlying type of E: <pre class="code-example">
E operator +(E x, U y);
E operator +(U x, E y);
</pre><span class="sentence"><span class="sentence-number">20</span> <a name="P2S20"></a>The operators are evaluated exactly as (E)((U)x + (U)y).</span> </span></li><li><span class="sentence"><span class="sentence-number">21</span> <a name="P2S21"></a> String concatenation: <pre class="code-example">
string operator +(string x, string y);
string operator +(string x, object y);
string operator +(object x, string y);
</pre><span class="sentence"><span class="sentence-number">22</span> <a name="P2S22"></a>The binary + operator performs string concatenation when one or both operands are of type string.</span> <span class="sentence"><span class="sentence-number">23</span> <a name="P2S23"></a>If an operand of string concatenation is null, an empty string is substituted.</span> <span class="sentence"><span class="sentence-number">24</span> <a name="P2S24"></a>Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object.</span> <span class="sentence"><span class="sentence-number">25</span> <a name="P2S25"></a>If ToString returns null, an empty string is substituted.</span> </span><span class="example">[Example: <pre class="code-example">
using System;
class Test
{
static void Main() {
string s = null;
Console.WriteLine("s = >" + s + "<"); // displays s = ><
int i = 1;
Console.WriteLine("i = " + i); // displays i = 1
float f = 1.2300E+15F;
Console.WriteLine("f = " + f); // displays f = 1.23E+15
decimal d = 2.900m;
Console.WriteLine("d = " + d); // displays d = 2.900
}
}
</pre>end example]</span> <span class="sentence"><span class="sentence-number">26</span> <a name="P2S26"></a>The result of the string concatenation operator is a string that consists of the characters of the left operand followed by the characters of the right operand.</span> <span class="sentence"><span class="sentence-number">27</span> <a name="P2S27"></a>The string concatenation operator never returns a null value.</span> <span class="sentence"><span class="sentence-number">28</span> <a name="P2S28"></a>A System.OutOfMemoryException may be thrown if there is not enough memory available to allocate the resulting string.</span> </li><li><span class="sentence"><span class="sentence-number">29</span> <a name="P2S29"></a> Delegate combination.</span> <span class="sentence"><span class="sentence-number">30</span> <a name="P2S30"></a>Every delegate type implicitly provides the following predefined operator, where D is the delegate type: <pre class="code-example">
D operator +(D x, D y);
</pre><span class="sentence"><span class="sentence-number">31</span> <a name="P2S31"></a>The binary + operator performs delegate combination when both operands are of some delegate type D.</span> <span class="sentence"><span class="sentence-number">32</span> <a name="P2S32"></a>(If the operands have different delegate types, a compile-time error occurs.)</span> <span class="sentence"><span class="sentence-number">33</span> <a name="P2S33"></a>If the first operand is null, the result of the operation is the value of the second operand (even if that is also null).</span> <span class="sentence"><span class="sentence-number">34</span> <a name="P2S34"></a>Otherwise, if the second operand is null, then the result of the operation is the value of the first operand.</span> <span class="sentence"><span class="sentence-number">35</span> <a name="P2S35"></a>Otherwise, the result of the operation is a new delegate instance that, when invoked, invokes the first operand and then invokes the second operand.</span> </span><span class="note">[Note: For examples of delegate combination, see <a href="14.7.5.htm">§14.7.5</a> and <a href="22.3.htm">§22.3</a>. Since System.Delegate is not a delegate type, operator + is not defined for it. end note]</span> </li></ul></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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