你能帮我理解这个程序吗？

Question

Can you help me out to understand why I'm getting this output.

#include<stdio.h>
#include<string.h>
void main() {
char a[] = "Hello World";
char *p;
p=a;
printf("%d%d%d%d",sizeof(a),sizeof(p),strlen(a),strlen(p));
}

output: 1281111 (My OS is of 64-bits)

Saying that the above code should have shown 1241111(output) if It is compiled and ran on a 32-bit system. Due to 64-bit It shows 1281111.

In my First year, I saw this question and when I went to look for the output, I get 1281111.

But surprisingly above code's output has two options:1)12121111 and 2)1221111.(University Question).

Answer 1

If you change the printf() statement to the following, it's easier to see what's going on:

printf("%d\n%d\n%d\n%d\n",sizeof(a),sizeof(p),strlen(a),strlen(p));

On my system, this results in the output:

12
8
11
11

In other words:

• The size of the array is 12 bytes. (11 for the string, plus one for the \\0 character.)
• The size of the pointer is 8 bytes (because I'm using a computer with 64-bit memory addresses, as opposed to a 32-bit computer which would likely output 4 ).
• When used as strings ( char* pointers), a and p are equivalent. (because p points to a .) The length of the string Hello World is 11 (since strlen() doesn't include the \\0 byte at the end of the string).

Hope this helps.