String constants for C + +

Today to do a pen test of Baidu, the title is such, the use of C + + language to write a function, to achieve the reversal of the string, requires no system functions, and the time complexity of the least. The function prototype is: Char *reverse_str (char *str).
After a few thoughts, wrote the following code on the VC6.0: #include <stdio.h>char *reverse_str (char *str);

void Main ()
{
char* s = "ABCD";
printf ("%s\n", Reverse_str (s));
}

Char *reverse_str (char *str)
{
     Char *p=str,*q=str,t;
    while (*q!= ')
    q++;
    q--;
    while (P&LT;Q)
    {
        t = *p;
        *p = *q;
        *q = t;
        p++;
        q--;
    }
    return str;
}

As a result, the debug encountered 0xc0000005:access violation error. The understanding of C + + string constants is involved here. 1. Local variables are stored in the stack, 2. Global variables, static variables are stored in static storage, 3.new of memory is in the heap, and 4. String constants are also stored in the static storage area.
Note: The variable memory in the stack is automatically freed with the end of the defined interval, and for the heap, manual free is required. For static stores, the variable constants are persisted during the run of the program, are not freed, and have only one copy.
Char *s = "ABCD"; defines a string constant stored in a static storage area. It cannot be modified by a pointer. In fact, the usual notation is const char *s = "ABCD"; If you want to modify the string contents, you should define the string variable as follows: char s[5] = "ABCD"; note that the character array is 1 more than the number of visible characters because the compiler adds the character ' Identifies as a string end. So, the following test code: Char *str1 = "ads";
Char *str2 = "ads";
Char *STR3 = "ads";
Char str4[4] = "ads";
Char str5[4] = "ads";

if (STR1==STR2)
cout<< "STR1==STR2" <<endl;
if (STR2==STR3)
cout<< "STR2==STR3" <<endl;
if (STR3!=STR4)
cout<< "STR3!=STR4" <<endl;
if (STR4!=STR5)
cout<< "STR4!=STR5" <<endl;
The output is:STR1==STR2
Str2==str3str3!=str4STR4!=STR5
Go back to the beginning of the code, make the following changes, you can successfully execute. #include <stdio.h>Char *reverse_str (char *str);

void Main ()
{
char s[5] = "ABCD";
printf ("%s\n", Reverse_str (s));
}

Char *reverse_str (char *str)
{
    Char *p=str,*q=str,t;
    While (*q!= ')
    q++;
    q--;
    While (P<Q)
    {
        t = *p;
        *p = *q;
        *q = t;
        p++;
        q--;
    }
    return str;
}

String constants for C + +