为什么char不带符号或不带符号，而wchar_t是带符号的? [英] Why is char neither signed or unsigned, but wchar_t is?

问题描述

以下C ++程序可正确编译:

The following C++ program compiles without errors:

void f(char){}
void f(signed char){}
void f(unsigned char){}
int main(){}  

同一程序的wchar_t版本没有:

void f(wchar_t){}
void f(signed wchar_t){}
void f(unsigned wchar_t){}
int main(){}

错误:重新定义了"void f(wchar_t)"
无效f(signed wchar_t){}

error: redefinition of ‘void f(wchar_t)’
void f(signed wchar_t){}

似乎wchar_t是unsigned.
为什么超载不一致?

It seems that wchar_t is unsigned.
Why is there an inconsistency in overloading?

推荐答案

char都是不同的类型，可以重载

The chars are all distinct types and can be overloaded

[基本原理]/1

[...]普通char，signed char和unsigned char是三种不同的类型， 统称为窄字符类型. [...]

[...] Plain char, signed char, and unsigned char are three distinct types, collectively called narrow character types. [...]

wchar_t也是一种独特的类型，但是不能用signed或unsigned限定，它们只能与标准整数类型一起使用.

wchar_t is also a distinct type, but it cannot be qualified with signed or unsigned, which can only be used with the standard integer types.

[dcl.type]/2

[dcl.type] / 2

通常，最多允许一个 type-specifier 声明的完整 decl-specifier-seq 或 type-specifier-seq 或 trailing-type-specifier-seq .唯一的例外 该规则如下:

As a general rule, at most one type-specifier is allowed in the complete decl-specifier-seq of a declaration or in a type-specifier-seq or trailing-type-specifier-seq. The only exceptions to this rule are the following:

[...]

signed或unsigned可以与char，long，short或int组合.

signed or unsigned can be combined with char, long, short, or int.

[dcl.type.simple]/2

[dcl.type.simple] / 2

[...]表9总结了简单类型说明符及其指定类型的有效组合.

[...] Table 9 summarizes the valid combinations of simple-type-specifiers and the types they specify.

wchar_t的签名是由实现定义的:

The signedness of wchar_t is implementation defined:

[基本知识]/5

[...]类型wchar_t必须具有相同的大小，符号和对齐方式 要求(3.11)作为其他整数类型之一，称为 基础类型.

[...] Type wchar_t shall have the same size, signedness, and alignment requirements (3.11) as one of the other integral types, called its underlying type.

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