什么是整数文字类型？以及它们如何存储？ [英] What Are Integer Literal Type? And How They Are Stored?

问题描述

我刚刚开始学习C，现在有一个问题困扰了我一段时间。如果我写

I have just started learning C and a question has bugged me for a while now. If I write

int i = -1;
unsigned int j = 2;
unsigned int k = -2;

整数常量 -1 和 2 和 -2 ，以及如何将其转换为存储在 signed中int 和 unsigned int ？

What is the type of integer literal -1 and 2 and -2, and how does it get converted to get stored in signed int and unsigned int?

带符号整数是什么意思，变量或整数文字的属性也是吗？像 -2 是有符号整数而 2 是无符号整数吗？

What is meant by signed integer, is that the property of variable or integer literal too? Like -2 is signed integer and 2 is unsigned integer?

推荐答案

首先， -1 不是整数常量。该表达式由应用于常量 1 的一元-运算符组成。

First off, -1 is not an integer constant. It's an expression consisting of a unary - operator applied to the constant 1.

在C99和C11中，十进制整数常量的类型是 int ， long int 或 long long int ，其值将适合其中。同样，八进制或十六进制文字的类型为 int ， unsigned int ， long int ， unsigned long int ， long long int 或 unsigned long long int 。有关详细信息，请参见 N1570 6.4.4.1 。

In C99 and C11, the type of a decimal integer constant is the first of int, long int, or long long int in which its value will fit. Similarly, an octal or hexadecimal literal has type int, unsigned int, long int, unsigned long int, long long int, or unsigned long long int. The details are in N1570 6.4.4.1.

-1 和 -2 是常量表达式。一元-运算符的结果与操作数具有相同的类型（即使该结果导致溢出，如 -INT_MIN

-1 and -2 are constant expressions. The result of the unary - operator has the same type as the operand (even if that result causes an overflow, as -INT_MIN does in most implementations).

int i = -1;

常量 1 和表达式 -1 均为 int 类型。该值存储在 int 对象 i 中；无需转换。 （严格来说，它是从 int 转换为 int 的，但这没关系。）

The constant 1 and the expression -1 are both of type int. The value is stored in the int object i; no conversion is necessary. (Strictly speaking, it's converted from int to int, but that doesn't matter.)

unsigned int j = 2;

2 类型为 int 。它从 int 转换为 unsigned int 。

2 is of type int. It's converted from int to unsigned int.

unsigned int k = -2;

-2 类型为 int 。它从 int 转换为 unsigned int 。这次，由于 -2 不在 unsigned int 的范围之外，因此转换是不平凡的；结果是 UINT_MAX-1 。

-2 is of type int. It's converted from int to unsigned int. This time, because -2 is outside the range of unsigned int, the conversion is non-trivial; the result is UINT_MAX - 1.

某些术语：

常量被其他一些语言称为文字。它是代表恒定值的单个令牌。例如 1 和 0xff 。

A constant is what some other languages call a literal. It's a single token that represents a constant value. Examples are 1 and 0xff.

A constant expression 是在编译时需要评估的表达式。常数是常数表达式；其操作数是常量或常量表达式的表达式也是如此。例如 -1 和 2 + 2 。

A constant expression is an expression that's required to be evaluated at compile time. A constant is a constant expression; so is an expression whose operands are constants or constant expressions. Examples are -1 and 2+2.

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