++i 在C 为什么不是左值

shihyu

++i 在C 为什么不是左值 , 但是在C++ 是左值

1. #include <stdio.h>
   
2. 
   
3. int main(void)
   
4. {
   
5.           int c = 0;
   
6.           ++c = 100;
   
7.           printf("c = %d\n",c);
   
8.           return 0;
   
9. }

复制代码

gcc 无法编译成功 , g++ 可以

谢谢

[ 本帖最后由 shihyu 于 2009-3-14 09:00 编辑 ]

ztz0223

有吗？

alexhappy

常量可以是左值么？？？

雨过白鹭洲

规定就是规定，或许以后会变成你期望的方式

scutan

原帖由 shihyu 于 2009-3-14 08:10 发表
++i 在C 为什么不是左值 , 但是在C++ 是左值


#include

int main(void)
{
          int c = 0;
          ++c = 100;
          printf("c = %d\n",c);
          return 0;
}

gcc 无法编译 ...

C标准规定的. 在 6.3.2节中

1 Anlvalue is an expression with an object type or an incomplete type other than void;53)
if an lvalue does not designate an object when it is evaluated, the behavior is undefined.
When an object is said to have a particular type, the type is specified by the lvalue used to
designate the object. A modifiable lvalue is an lvalue that does not have array type, does
not have an incomplete type, does not have a const-qualified type, and if it is a structure
or union, does not have any member (including, recursively, any member or element of
all contained aggregates or unions) with a const-qualified type.

2 Except when it is the operand of the sizeof operator, the unary & operator, the ++
operator, the -- operator, or the left operand of the . operator or an assignment operator,
an lvalue that does not have array type is converted to the value stored in the designated
object (and is no longer an lvalue). If the lvalue has qualified type, the value has the
unqualified version of the type of the lvalue; otherwise, the value has the type of the
lvalue. If the lvalue has an incomplete type and does not have array type, the behavior is
undefined.

MMMIX

原帖由 shihyu 于 2009-3-14 08:10 发表
++i 在C 为什么不是左值 , 但是在C++ 是左值

C 和 C++ 是两种不同的语言，你怎么能指望它们的语义相同？