c++ - 在模板中使用#define VALUE

Question

我无法将定义的值传递给模板。即使是简单的计算也行不通:

    #define IR_TIMEOUT 564*173/2
    return decodeSpace<IR_TIMEOUT>(
    duration);

    return decodeSpace<564*173/2>(
    duration);

工作:

    return decodeSpace<48786>(
    duration);

定义:

    template <uint16_t irTimeout>
    bool decodeSpace(unsigned long duration){}

错误:

E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp: In member function 'virtual bool IRLprotocolNEC::decodeIR(long unsigned int)': E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp:46:11: error: no matching function for call to 'IRLprotocolNEC::decodeSpace(long unsigned int&)' duration); ^ E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp:46:11: note: candidate is: In file included from E:\Arduino\sketchbook\libraries\IRLremote/IRLprotocolNEC.h:27:0, from E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp:24: E:\Arduino\sketchbook\libraries\IRLremote/CIRLremote.h:103:9: note: template bool CIRLprotocol::decodeSpace(long unsigned int) bool decodeSpace(unsigned long duration){ ^ E:\Arduino\sketchbook\libraries\IRLremote/CIRLremote.h:103:9: note: template argument deduction/substitution failed: E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp:46:11: error: overflow in constant expression [-fpermissive] duration); ^ E:\Arduino\sketchbook\libraries\IRLremote\IRLprotocolNEC.cpp:46:11: note: in template argument for type 'unsigned int'

这是错误还是功能？或者更好:我怎样才能避免/解决这样的事情？

我想创建结构相同但时序不同的不同解码函数。传递值需要大量的闪存，所以我最好一遍又一遍地复制函数。这就是我想使用模板的原因。

Answer 1

问题是 564*173 溢出了 uint16。

当涉及到常量折叠时，使用定义或直接表达式是一回事。

常量折叠是编译器“展开”你的表达式的事实。例如，将“2*3”替换为“6”。