C ++ 11转换错误

Question

我正在尝试调用int向量的模板，但我没有找到解决以下错误的方法（我已查看网站上的建议问题）：

D:\CodeBlocks\Tests\Templates\main.cpp|51|error: conversion from 'std::vector<std::vector<int>, std::allocator<std::vector<int> > >' to non-scalar type 'std::vector<int>' requested|

Bellow这是我的代码：

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
#include <string>
#include <functional>

template<typename C> C f(C x)
{
    return x;
}

template <class A, class B> typename std::vector<B> my_map(A fct,B v)
{
    int n = v.size();
    std::vector<B> r(n);
    int i;
    for(i=0;i<n;i++)
    {
        r[i]=(B) fct(v[i]);
    }
    return r;
}
int main()
{
   std::vector<int> mapvector {1,2,5,7,9};

   std::vector<int> ret = my_map(&f<int>,mapvector);

   std::copy(ret.begin(), ret.end(), std::ostream_iterator<int>(std::cout));

   return 0;
}

Answer 1

@Autowired
public void configAuthentication(AuthenticationManagerBuilder auth) 
    throws Exception {

    auth.jdbcAuthentication().dataSource(dataSource)
        .passwordEncoder(passwordEncoder())
        .usersByUsernameQuery("sql...")
        .authoritiesByUsernameQuery("sql...");
}   

@Bean
public PasswordEncoder passwordEncoder(){
    PasswordEncoder encoder = new BCryptPasswordEncoder();
    return encoder;
}