Question

如果我写:

char arr[8] = "abc";

Is there any specification over what arr[4] might be? I did some tests with Clang and it seems that the remaining chars in the array are set to null. Also, char arr[8] = ""; zeroes every byte. Not sure if this is a compiler convenience, standard behavior, pure coincidence or I got it wrong.

void a()
{
    char arr[8] = "abc";    /* breakpoint here, line 3 */
    strcpy(arr, "1234567");
}
int main()
{
    a();
    a();
    return 0;
}

夸张记录:

Breakpoint 1, a () at str.c:3
3           char arr[8] = "abc";
(gdb) s
Current language:  auto; currently minimal
4           strcpy(arr, "1234567");
(gdb) p arr
$1 = "abc00000000"
(gdb) c      
Continuing.

Breakpoint 1, a () at str.c:3
3           char arr[8] = "abc";
(gdb) p arr
$2 = "1234567"
(gdb) s
4           strcpy(arr, "1234567");
(gdb) p arr
$3 = "abc00000000"

Answer 1

它具有标准的行为。

arr[3]被初步确定为0,因为终止0是说明字面的一部分。

其余部分均已初步确定为0,ISO/IEC 9899:<1999>a>, 6.7.8,21:

If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.

And char objects with static storage are initialized to 0.

Answer 2

char arr[8] = "abc";

完全等于

char arr[8] = { a ,  b ,  c ,   };

ISO C 6.7.8 §21指出:

If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.

In plain English this means that all values at the end of your array will be set to 0. So the standard guarantees that your code is equivalent to:

char arr[8] = { a ,  b ,  c ,   , 0, 0, 0, 0};

当然,的数值也是零。

This rule is universal to all arrays and not just to strings. Also, the same applies when initializing a struct but only explicitly setting a few of its members (6.7.8 §18).

This is why you can write code like

char arr[8] = "";

In this example, the first element of the array is initialized explicity to , and the rest of the items implicitly to zero. The compiler translates this to

char arr[8] = {0, 0, 0, 0, 0, 0, 0, 0};

Answer 3

这是标准行为。未明确入门的阵列的每一部分,如果在声明中初步确定阵列的任何序号,则先入为违约值(<>code >。它还从事其他类型的工作:

int a[10] = {1};

zeroes out a[1] through a[9].

Answer 4

根据该标准,除具体规定外的所有指数都将定为零/年。 https://stackoverflow.com/q/1352379/900873”

友情链接