是的，一元
#include <stdio.h>
int main() {
int a;
char b;
short int c;
double d;
printf("%d %d %d %dn", sizeof(a), sizeof(b), sizeof(c), sizeof(d));
printf("%d %d %d %dn", sizeof(+a), sizeof(+b), sizeof(+c), sizeof(+d));
printf("%d %d %d %dn", sizeof(-a), sizeof(-b), sizeof(-c), sizeof(-d));
return 0;
}
32位编译器输出：
4 1 2 84 4 4 84 4 4 8
如果我像sizeof(-a)一样更改sizeof()内部的符号，则输出是相同的。我想知道为什么会发生这种事。+和-运算符是否在推广数据类型？
+和-运算符integer将小整数类型提升为int。C17 6.5.3.3：
一元+运算符的结果是其(提升(操作数的值。整数对操作数执行提升，结果具有提升类型。
一元运算符的结果是其(提升的(操作数的负数。整数对操作数执行提升，结果具有提升类型。
有关整数提升的详细信息，请参阅隐式类型提升规则。
你可以玩_Generic来找出任何表达式的实际类型：
#include<stdio.h>
#define type(x) _Generic((x),
int: puts(#x " is int"),
short: puts(#x " is short"),
char: puts(#x " is char") );
int main (void)
{
int a;
char b;
short int c;
type(a); type(+a);
type(b); type(+b);
type(c); type(+c);
}
输出：
a is int
+a is int
b is char
+b is int
c is short
+c is int
正是这样。当进行计算时(例如+或-(，较短的整数格式会提升到基本大小，即int，即4字节长。
当在简单算术表达式中用作参数时，小整数类型会升级为int或unsigned int。因此，sizeof(b)是1，相当于char的大小，但sizeof(+b)是4，相当于您平台上的int的大小。
但是请注意，printf期望%d转换规范有一个int参数。sizeof()具有类型size_t，这是一种可能不同于unsigned int的无符号类型。您应该使用%zu或将sizeof()表达式强制转换为(int)。
下面是一个示例程序：
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#define typeof(X) _Generic((X),
long double: "long double",
double: "double",
float: "float",
unsigned long long int: "unsigned long long int",
long long int: "long long int",
unsigned long int: "unsigned long int",
long int: "long int",
unsigned int: "unsigned int",
int: "int",
unsigned short: "unsigned short",
short: "short",
unsigned char: "unsigned char",
signed char: "signed char",
char: "char",
bool: "bool",
__int128_t: "__int128_t",
__uint128_t: "__uint128_t",
default: "other")
int main() {
int a;
char b;
short int c;
#define TEST(x) printf("%8s has type %s and size %zun", #x, typeof(x), sizeof(x))
TEST(a);
TEST(+a);
TEST(b);
TEST(+b);
TEST(c);
TEST(+c);
TEST('0');
TEST(*"");
TEST(0);
TEST(0L);
TEST(0LL);
TEST(0.F);
TEST(0.);
TEST(0.L);
TEST(sizeof(a));
return 0;
}
64位操作系统/X:上的输出
a has type int and size 4
+a has type int and size 4
b has type char and size 1
+b has type int and size 4
c has type short and size 2
+c has type int and size 4
'0' has type int and size 4
*"" has type char and size 1
0 has type int and size 4
0L has type long int and size 8
0LL has type long long int and size 8
0.F has type float and size 4
0. has type double and size 8
0.L has type long double and size 16
sizeof(a) has type unsigned long int and size 8