#include <iostream>
#include <boost/static_assert.hpp>
using namespace std;
// I understand how the following template function works
// template <class T>
// T GetMax (T a, T b) {
// T result;
// result = (a>b)? a : b;
// return (result);
// }
// I have difficulties to understand how the following code works
// when we should use this syntax
template<int i> void accepts_values_between_1_and_10() {
BOOST_STATIC_ASSERT(i >=1 && i < 10);
cout << "i(between 1 and 10): " << i << endl;
}
// I created the following function to test the understanding of BOOST_STATIC_ASSERT
template<typename T> void accepts_values_between_1_and_10_alternative(T i) {
BOOST_STATIC_ASSERT(i >=1 && i < 10);
cout << "i(between 1 and 10): " << i << endl;
}
int main () {
const int i = 5;
accepts_values_between_1_and_10<i>();
const int j = 6;
accepts_values_between_1_and_10_alternative(j);
return 0;
}
// $> g++ -o template_function -Wall -g template_function.cpp
// template_function.cpp: In function ‘void accepts_values_between_1_and_10_alternative(T) [with T = int]’:
// template_function.cpp:33:48: instantiated from here
// template_function.cpp:23:1: error: ‘((i > 0) && (i <= 9))’ is not a valid template argument for type ‘bool’ because it is a non-constant expression
问题1>以下语句的语法是什么?我们应该在何时使用它?如果这是一个模板特化,为什么我们需要提供一个参数而不只是
template<int> void accepts_values_between_1_and_10()
instead of
template<int i> void accepts_values_between_1_and_10()
template<int> void accepts_values_between_1_and_10(int i)
instead of
template<int i> void accepts_values_between_1_and_10()
问题2> 如果我们必须使用这种形式,那么在函数作用域内采用这种语法是真实的吗?
问题3> 如何纠正accepts_values_between_1_and_10_alternative
的定义,以使其与BOOST_STATIC_ASSERT
一起工作?
谢谢
static_assert
语言结构,因此您将不再需要 Boost。 - Kerrek SB