g ++给出错误：类型'char&'的引用的无效初始化来自'unsigned char'类型的表达式 [英] g++ gives error : invalid initialization of reference of type ‘char&’ from expression of type ‘unsigned char’

问题描述

当我尝试编译以下代码

int main()
{
    unsigned char uc;
    char & rc = uc;
}

g ++会出现以下错误：char&从表达式的'unsigned char'。使用signed char而不是unsigned char时也会发生同样的情况。
但下面的编译很好

g++ gives the following error : invalid initialization of reference of type ‘char&’ from expression of type ‘unsigned char’. The same happens when using signed char instead of unsigned char. But the following compiles well

int main()
{
    unsigned char uc;
    const char & rc = uc;
}

为什么不能用变量初始化'char&'类型为'unsigned char'，但可以用它初始化'const char&'？

Why isn't it possible to initialize 'char &' with a variable of type 'unsigned char' while it is possible to initialize 'const char &' with it?

推荐答案

是不是可以用'unsigned char'类型的变量初始化'char&'，而且可以用它初始化'const char&'？

Why isn't it possible to initialize 'char &' with a variable of type 'unsigned char' while it is possible to initialize 'const char &' with it?

因为当 unsigned char 转换为 char ，你不能用非const引用。 char ， signed char 和 unsigned char 类型，如C ++ 11§3.9.1中所述：

Because the latter creates a temporary to bind to the const reference when the unsigned char is converted to a char, something you can't do with non-const references. char, signed char, and unsigned char are three distinct types, as explained in C++11 § 3.9.1:

Plain char，signed char和unsigned char是三种不同类型

Plain char, signed char, and unsigned char are three distinct types

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