程序中寫過這樣幾個函數：

extractUInt
?1unsigned?int?extractUInt(byte?*element)
?2{
?3????byte?id?=?0;
?4????byte?*decodedUInt?=?NULL;
?5????unsigned?short?decodedUIntLength?=?ElementHandler::decode(element,?&id,?&decodedUInt);
?6????unsigned?int?ui?=?0;
?7????memcpy_s(&ui,?sizeof(ui),?decodedUInt,?decodedUIntLength);
?8
?9????delete?[]decodedUInt;
10????return?ui;
11}
extractUShort
?1unsigned?short?extractUShort(byte?*element)
?2{
?3????byte?id?=?0;
?4????byte?*decodedUShort?=?NULL;
?5????unsigned?short?decodedUShortLength?=?ElementHandler::decode(element,?&id,?&decodedUShort);
?6????unsigned?short?us?=?0;
?7????memcpy_s(&us,?sizeof(us),?decodedUShort,?decodedUShortLength);
?8
?9????delete?[]decodedUShort;
10????return?us;
11}
extractByte
?1byte?extractByte(byte?*element)
?2{
?3????byte?id?=?0;
?4????byte?*decodedByte?=?NULL;
?5????unsigned?short?decodedByteLength?=?ElementHandler::decode(element,?&id,?&decodedByte);
?6????byte?by?=?0;
?7????//memcpy_s(&by,?sizeof(by),?decodedByte,?decodedByteLength);
?8????by?=?*decodedByte;
?9
10????delete?[]decodedByte;
11????return?by;
12}
寫的時候并未覺得異樣，昨天再次查看的時候才發現三個函數語義重復，僅返回值不同，于是想到模板函數。想當然地寫成了這樣:

Code
?1template<class?T>
?2T?extractNumber(byte?*element)
?3{
?4????byte?id?=?0;
?5????byte?*decoded?=?NULL;
?6????unsigned?short?decodedLength?=?ElementHandler::decode(element,?&id,?&decoded);
?7
?8????T?t?=?0;
?9????memcpy_s(&t,?sizeof(t),?decoded,?decodedLength);
10
11????delete?[]decoded;
12????return?t;
13}
編譯時未報錯，但在調用時

1unsigned?short?us?=?extractNumber(element);
會出現編譯錯誤，提示無法為“T”推導模板參數。改成如下模樣即可解決問題：

1unsigned?short?us?=?extractNumber<unsigned?short>(element);

轉載于:https://www.cnblogs.com/tonyyang132/archive/2009/10/14/1583123.html

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