将 unsigned 转换为 complex<int> 会导致符号转换警告

Question

考虑以下代码：

#include <complex>

int main()
{
    unsigned u = 1u;
    auto result = static_cast<std::complex<int>>(u);
    return 0;
}

编译

g++ -std=c++11 -Werror -Wsign-conversion -o a.out source_file.cpp

导致编译错误

source_file.cpp: In function ‘int main()’:
source_file.cpp:8:51: error: conversion to ‘int’ from ‘unsigned int’ may change the sign of the result [-Werror=sign-conversion]
     auto result = static_cast<std::complex<int>>(u);
                                                   ^

clang 报类似错误

source_file.cpp:6:50: error: implicit conversion changes signedness: 'unsigned int' to 'const value_type' (aka 'const int') [-Werror,-Wsign-conversion]
    auto result = static_cast<std::complex<int>>(u);
                  ~~~~~~~~~~~                    ^

这个错误乍一看没有多大意义，我错过了什么？

Answer 1

您收到的转换警告不是来自转换，而是来自内部 std::complex 的构造。

对于 'fix' 你的例子你应该改为：

auto result = std::complex<int>{static_cast<int>(u)};

将 unsigned 转换为 complex<int> 会导致符号转换警告

casting unsigned to complex<int> causes sign-conversion warning

c++

compiler-warnings