String reverse error

Can anyone explain to m开发者_如何学运维e why im getting a ".exe has encountered a problem and needs close"error, it compiles and works sometimes when i fiddle with the char array, but when it does work i sometimes get strange characters at the end of the string.

    #include <iostream>
using namespace std;
char* StrReverse3(char*);
char* StrReverse3(char* str)
{
    char *p;

    int length=0,start=0,end=0;
    length=strlen(str);

    for(start=0,end=length-1;end>= 0,start<=length-1;end--,start++)
    {
        p[start]=str[end];
    }   


    return p;
}
int main()
{
  char str[100]="Saw my reflection in snow covered hills";
  StrReverse3(str);

cin.get();
return 0;
}

---

You are not initializing p. It's an uninitialized pointer that you are writing to.

Since you are writing this in C++, not C, I'd suggest using std::string and std::reverse:

#include <string>
#include <algorithm>
#include <iostream>

int main()
{
    std::string str = "Saw my reflection in snow covered hills";
    std::reverse(str.begin(), str.end());
    std::cout << str;
    return 0;
}

Output:

sllih derevoc wons ni noitcelfer ym waS

See it working online at ideone

---

char *p; is never initialized, yet p[start] is used as the destination of an assignment. Don't you get compiler warnings from this? I'm amazed it even "works sometimes".

---

You are accessing memory that wasn't allocated by your program (p can point anywhere!). This is the reason for the problems you have.

I strongly encourage you to

• read into the topic of dynamically allocating memory with new and delete to understand a very important topic
• read into the standard template library, especially std::string. You should not use raw pointers like char*, always use standard types when possible.

---

#include <iostream>
#include <cstring>

using namespace std;

char* StrReverse3(char* str){
    int length=0,start=0,end=0;
    length=strlen(str);

    for(start=0,end=length-1;end > start;end--,start++){
        char temp;
        temp = str[start];
        str[start]=str[end];
        str[end]=temp;
    }

    return str;
}
int main(){
  char str[100]="Saw my reflection in snow covered hills";
  cout << StrReverse3(str);
  cin.get();
  return 0;
}