如何在不强制转换每个参数的情况下在初始值设定项列表中删除从 int 到 char 的缩小转换？

Question

Here's what i tried to do: (with comparison to std::vector<int> )

char s = 4;
std::vector<int> i;
std::vector<char> c;

i.insert(i.end(),{s+1,s+2,s+3}); // no warnings
c.insert(c.end(),{s+1,s+2,s+3}); // narrowing conversions of {s+1,s+2,s+3} from ints to chars

I know i can cast, but that gets ugly quickly. (especially with more arguments)

c.insert(c.end(),{(char)(s+1),(char)(s+2),(char)(s+3),(char)(s+4),(char)(s+5),(char)(s+6)});

Do we have to live with this? Or is there a better way?

Answer 1

Narrowing conversion in an initializer_list is a problem. See the answers to warning: narrowing conversion C++11 .

You can use a helper function to get around the problem.

namespace MyApp
{
   char next(char c, int n) { return c+n; }
}

and use it as

c.insert(c.end(), {MyApp::next(s, 1), MyApp::next(s, 2), MyApp::next(s, 3)});

Answer 2

If your list is regular, you could use a loop instead like

for (int i = 1; i <= 3; ++1)
{
    c.insert(c.end(), s + i);
}

If it s not regular, you could build a std::initializer_list , and then use insert 's range overload to insert into the vector like

{
    auto elems  = {s+1,s+2,s+3};
    c.insert(c.end(), elems.begin(), elems.end());
}