strlen

char c1[] = "sdfa";//系统自动添加结束字符 \0

char c2[] = {'1','2','3'};//这样赋值的话，要自己加上结束字符 \0

printf("%s\t %s\n",c1,c2);

printf("%lu\t %lu\n",strlen(c1),sizeof(c2));//strlen获得字符串长度，不包括\0