[C/C++] char* 和 char[] 使用差別

char *p = "abc"; // 指標宣告, "abc"這個陣列會放在記憶體的"常數區塊",不允許被修改
char q[] = {'a','b','c',0}; // 陣列宣告,同時給予初始值
char r[] = "abc"; // 陣列宣告, 此空間就放在堆疊上
q[0] = '!'; // q字串變成 "!bc"
r[0] = '!'; // r字串變成 "!bc"
*p = '!'; // 這在Unix系統上會造成Segmentation fault (core dumped)

#include <iostream>
#include <string.h>
#include <stdlib.h>

using namespace std;

char * strcopy(char *dest, char *from)
{
    char *p = dest;
    while(*dest++ = *from++)
    ;
    return p;
}

char * strconcat(char *dest, char *from)
{
    char *p = dest;
    while(*dest) dest++;
    
    while(*dest++ = *from++)
    ;
    
    return p;
}

char * strrever(char *dest)
{
    char *p = dest;
    char *pt = dest;
    
    while(*dest) dest++;
    ; 
    for(--dest; pt < dest; pt++, dest--)   
    {
        *pt = *pt ^ *dest;
        *dest = *pt ^ *dest;
        *pt = *pt ^ *dest;   
    }
   
    return p;
}


int main()
{
   //char str1[]="123      ";           // dest須給足空間 否則會有問題
   //char *str1 = "123456789"           // error 指標已指定長數空間 不能更改其內容
   char *str1 = (char *)malloc(20);     // dest須給足空間 否則會有問題
   char *str2="abcdef";
   
   char *str3 = strcopy(str1, str2);
   
   cout << str1 <<endl;
   cout << str2 <<endl;
   cout << str3 <<endl;
   
   //strcat(str1, str2);
   char *str4 = strconcat(str1, "test");
   
   cout << str1 <<endl;
   cout << str2 <<endl;
   cout << str4 <<endl;
   
   char *str5 = strrever(str1);
   
   cout << str1 <<endl;
   cout << str2 <<endl;
   cout << str5 <<endl;
   
   return 0;
}