C++ 模板特化语法
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C++ templates specialization syntax
提问by Jan Turoň
In C++ Primer Plus (2001, Czech Translation) I have found these different template specialization syntax:
在 C++ Primer Plus（2001，捷克语翻译）中，我发现了这些不同的模板特化语法：
function template
功能模板
template <typename T> void foo(T);
specialization syntax
专业化语法
void foo(int param); // 1
void foo<int>(int param); // 2
template <> void foo<int>(int param); // 3
template <> void foo(int param); // 4
template void foo(int param); // 5
Googling a bit, I have found only No.3 examples. Is there any difference (in call, compiling, usage) among them? Are some of them obsolete/deprecated? Why not just use No.1?
谷歌搜索了一下，我只找到了第 3 个例子。它们之间有什么区别（在调用、编译、使用方面）？其中一些是否已过时/已弃用？为什么不直接使用 No.1？
回答by Nawaz
Here are comments with each syntax:
以下是每种语法的注释：
void foo(int param); //not a specialization, it is an overload
void foo<int>(int param); //ill-formed
//this form always works
template <> void foo<int>(int param); //explicit specialization
//same as above, but works only if template argument deduction is possible!
template <> void foo(int param); //explicit specialization
//same as above, but works only if template argument deduction is possible!
template void foo(int param); //explicit instantiation
Added by me:
由我添加：
//Notice <int>. This form always works!
template void foo<int>(int param); //explicit instantiation
//Notice <>. works only if template argument deduction is possible!
template void foo<>(int param); //explicit instantiation
From coding point of view, overload is preferred over function-template-specialization.
从编码的角度来看，重载优于函数模板特化。
So, don't specialize function template:
所以，不要专门化函数模板：
And to know the terminologies:
并了解术语：
- instantiation
- explicit instantiation
- specialization
- explicit specialization
- 实例化
- 显式实例化
- 专业化
- 明确的专业化
See this :
看到这个：
回答by gerardw
Using Visual Studio 2012, it seems to work slightly different if there's no function argument:
使用 Visual Studio 2012，如果没有函数参数，它的工作似乎略有不同：
template <typename T> T bar( );
//template int bar<int>( ) { return 0; } doesn't work
template < > int bar<int>( ) { return 0; } //does work
