C语言什么时候支持结构体变量之间直接赋值
struct A
{
int a1;
int a2;
}A1,A2;
.....
A1=A2?
这种直接赋值什么时候可以的啊，我记得以前谭老师的书说这种是错误的
[解决办法]
谭浩强那本书最大的作用就是通过找其中的错误来检验自己的水平。
C语言直接支持结构体变量的赋值，它是按值逐元素赋值的。
参看K&R A.7.17 Assignment Expressions
In the simple assignment with =, the value of the expression replaces that of the object referred to by the lvalue. One of the following must be true: both operands have arithmetic type, in which case the right operand is converted to the type of the left by the assignment; or both operands are structures or unions of the same
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
type; or one operand is a pointer and the other is a pointer to void, or the left
~~~~
operand is a pointer and the right operand is a constant expression with value 0; or both operands are pointers to functions or objects whose types are the same except for the possible absence of const or volatile in the right operand.
进一步，C99标准§6.7.2.1上说：
struct s { int n; double d[]; };
……
struct s *s1;
struct s *s2;
……
The assignment:
*s1 = *s2;
only copies the member n and not any of the array elements.
而C99标准的TC2 Committee Draft则进一步指出：
if any of the array elements are within the first sizeof (struct s) bytes
of the structure, they might be copied or simply overwritten with indeterminate values.
