C语言-求字符串长度-strlen()与sizeof()

#include <string.h>

char s1[20] = "hello world";
char s2[20] = {'h','e','l','l','0',' ','w','o','r','l','d','\0'};
char s3[] = "hello\0 world";
char s4[] = {'h','e','l','l','0','\0',' ','w','o','r','l','d','\0'};   
printf("%d\t%d\t%d\t%d\n",strlen(s1),strlen(s2),strlen(s3),strlen(s4));
printf("%d\t%d\t%d\t%d\n",sizeof(s1),sizeof(s2),sizeof(s3),sizeof(s4));
/*
输出：
11      11      5       5
20      20      13      13
*/