将std :: accumulate中的double转换为int转换警告

Question

How to force the gcc/clang to show a warning about converting double to int in such code (in particular when using std::accumulate for container of doubles but have result in integer):

#include <iostream>
#include <numeric>
#include <vector>

int main() {

    std::vector<double> v = { 0.5, 0.6, 0.7 };

    // gives wrong result due integer initial value
    std::cout << std::accumulate( v.begin(), v.end(), 0 ) << std::endl; // no warning

    int i = 4.2; // warning

    return 0;
}

-Wconversion does not work well. Link: http://goo.gl/efJUou

PS VS2013 reports about type deduction warning in template function, by which you can catch the error.

Answer 1

Warnings are disabled by default for system headers. You can use the option -Wsystem-headers to enable them, but the downside is that it will output additional irrelevant warnings.