C++ 函数模板返回值指定

C++函数模板不能偏特化，可以全特化。另外，返回值也是可以用static_cast指定的。
举例如下：

template<typename T1, typename T2, typename T3>T1 add(T2 a, T3 b){    return static_cast<int>(a + b);}

指定T1为int，代码如下:

    int result = add<int>(0.4, 0.9);

指定T1, T2参数为int和float，代码如下:

int result = add<int, float>(0.4, 0.9);

一个完整的利用函数模板指定函数返回值的例子如下:

#include <iostream>enum class AAA : int {    TYPE1 = 33,    TYPE2 = 52,    TYPE3 = 92,    TYPE4 = 102,    TYPE5 = 22,    TYPE6 = 8,    TYPE7 = 12,};enum class BBB : int {    TPYE1 = AAA::TYPE1,    TYPE3 = AAA::TYPE3,    TYPE5 = AAA::TYPE5,};enum class CCC : int {    TPYE2 = AAA::TYPE2,    TYPE3 = AAA::TYPE3,    TYPE5 = AAA::TYPE5,};AAA uec2AAA (int uec) {    AAA rc;    switch (uec) {        case 1:             rc = AAA::TYPE1;            break;        case 2:            rc = AAA::TYPE2;            break;        case 3:            rc = AAA::TYPE3;            break;        case 4:            rc = AAA::TYPE4;            break;        case 5:                rc = AAA::TYPE5;            break;        case 6:            rc = AAA::TYPE6;            break;        default:            break;        }    return rc;    }template<typename T1>T1 uec2Rc(int a){    return static_cast<T1>(uec2AAA(a));}int main(void){    BBB result = uec2Rc<BBB>(3);    printf("result = %d\n", static_cast<int>(result));    CCC result2 = uec2Rc<CCC>(2);    printf("result = %d\n", static_cast<int>(result2));    return 0;}

还有一些下次再写。