c - C 中合法的数组赋值语句

Question

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What is the difference between char s[] and char *s in C?
Difference between char *str = “…” and char str[N] = “…”?

我是 C 编程初学者。我对这些事情感到困惑:

char ar[]="hello";
char ar2[], *ar3;
ar2=ar;
ar3=ar;

对于 2D 数组，上述内容也是合法的，例如:

int arr[2][2]={{1,2},{3,4}};
int arr1[2][2],**arr2,*arr3;
arr1[0]=arr[0];
arr1=arr;
arr2=arr;
arr3=arr;

另一个令人困惑的是，我已经看到上面的结构在结构情况下是有效的。

struct test{
int ar[2];
} t1, t2;

int main()
{
t1.ar[0]=0;
t1.ar[1]=1;
t2.ar=t1.ar;
}

请耐心等待，我是 C 初学者。

Answer 1

char ar[] = "hello";
char ar2[];
char *ar3;

数组是一个不可修改的左值，因此以下语句无效:

ar2 = ar;

否则，可能会影响该值到指针。

ar3 = ar;

该行为与 2D 数组和结构成员相同。

C11 (n1570)

§ 6.3.2.1 Lvalues, arrays, and function designators
A modifiable lvalue is an lvalue that does not have array type [...].

§ 6.5.16 Assignment operators
An assignment operator shall have a modifiable lvalue as its left operand.