[英]C++: candidate template ignored: invalid explicitly-specified argument for template parameter
I have this function header: 我有这个函数头:
template <
bool src_alpha,
int sbpp, int dbpp,
typename T1, typename T2,
Color (*getFunc)(T1 data, Uint8* addr),
void (*putFunc)(T2 data, Uint8* addr, Color c)
>
static void OperateOnSurfaces(T1 data1, T2 data2, SDL_Surface * bmpDest, SDL_Surface * bmpSrc, SDL_Rect& rDest, SDL_Rect& rSrc)
This is how I use it: 这就是我使用它的方式:
OperateOnSurfaces<
true,
32, 32,
SDL_PixelFormat*, SDL_PixelFormat*,
GetPixel<true,32>, PutPixel<true,true,32> >(
bmpSrc->format, bmpDest->format,
bmpDest, bmpSrc, rDest, rSrc);
This is GetPixel
and PutPixel
: 这是
GetPixel
和PutPixel
:
template<bool alpha, int bpp>
static Color GetPixel(SDL_PixelFormat* format, Uint8* addr) { /* .. */ }
template<bool alpha, bool alphablend, int bpp>
static void PutPixel(SDL_PixelFormat* format, Uint8* addr, Color col) { /* .. */ }
And I get this error: 我收到这个错误:
note: candidate template ignored: invalid explicitly-specified argument for template parameter 'getFunc' [3]
Why? 为什么?
I suspect that all those functions are free functions. 我怀疑所有这些功能都是免费功能。 When you declare a free function
static
, it gains internal linkage. 当你声明一个自由函数
static
,它会获得内部链接。 Non-type template parameters, in C++03, must have external linkage † . C ++ 03中的非类型模板参数必须具有外部链接† 。 Just remove
static
in front of the functions. 只需删除函数前面的
static
。
template <
bool src_alpha,
int sbpp, int dbpp,
typename T1, typename T2,
char (*getFunc)(T1 data, unsigned* addr),
void (*putFunc)(T2 data, unsigned* addr, char c)
>
void OperateOnSurfaces(){}
template<bool alpha, int bpp>
char GetPixel(void* format, unsigned* addr);
template<bool alpha, bool alphablend, int bpp>
void PutPixel(void* format, unsigned* addr, char col);
int main(){
OperateOnSurfaces<
true,
32, 32,
void*, void*,
GetPixel<true,32>, PutPixel<true,true,32> >();
}
This modified example compiles fine on Clang 3.1 and GCc 4.4.5 in C++98 and C++11 mode, no warnings. 这个修改过的例子在C ++ 98和C ++ 11模式下在Clang 3.1和GCc 4.4.5上编译得很好,没有任何警告。 If I leave the
static
in, I get a similar error + note to what you got with Clang, and GCC spits out the vital information (scroll to the right, "has not external linkage"): 如果我保留
static
,我会得到一个类似的错误+注意你得到的Clang,并且GCC吐出重要信息(滚动到右边,“没有外部链接”):
15:02:38 $ g++ t.cpp
t.cpp: In function ‘int main()’:
t.cpp:21: error: ‘GetPixel<true, 32>’ is not a valid template argument for type ‘char (*)(void*, unsigned int*)’ because function ‘char GetPixel(void*, unsigned int*) [with bool alpha = true, int bpp = 32]’ has not external linkage
t.cpp:21: error: ‘PutPixel<true, true, 32>’ is not a valid template argument for type ‘void (*)(void*, unsigned int*, char)’ because function ‘void PutPixel(void*, unsigned int*, char) [with bool alpha = true, bool alphablend = true, int bpp = 32]’ has not external linkage
t.cpp:21: error: no matching function for call to ‘OperateOnSurfaces()’
† (C++03) §14.3.2 [temp.arg.nontype] p1
†
(C++03) §14.3.2 [temp.arg.nontype] p1
A template-argument for a non-type, non-template template-parameter shall be one of:
模板参数的用于非类型的,非模板的模板参数应是以下之一:
[...]
[...]
the address of an object or function with external linkage [...]
具有外部链接的对象或函数的地址 [...]
[...]
[...]
Note that C++11 changed the wording and allows functions with internal linkage too now: 请注意,C ++ 11现在改变了措辞并允许具有内部链接的功能:
(C++11) §14.3.2 [temp.arg.nontype] p1
A template-argument for a non-type, non-template template-parameter shall be one of:
模板参数的用于非类型的,非模板的模板参数应是以下之一:
[...]
[...]
a constant expression (5.19) that designates the address of an object with static storage duration and external or internal linkage or a function with external or internal linkage [...]
一个常量表达式(5.19),用于指定具有静态存储持续时间和外部或内部链接的对象的地址, 或具有外部或内部链接的函数 [...]
- [...]
[...]
Clang does currently not obey to this in C++11 mode, it still only allows functions with external linkage. Clang目前在C ++ 11模式下不遵守这一点,它仍然只允许具有外部链接的功能。
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