CODEWITHSUNDEEP
c++
klm_
klm_

Reputation: 1209

C++ cout pointer

Hello Can somebody explain why second cout in func(char *p) doesn't work:

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

using namespace std;

char *strhex(char *str);
char *func(char *p);

int  main()
{
     char *ptr;    

     char *p=strhex("d");
     cout<<"main:"<<p<<endl;

     cout<<func(p)<<endl;

     system("PAUSE");
     return 0;
}

char *func(char *p)
{ 
      cout<<"func1:"<<p<<endl;
      char buffer[500]="";
   char *zbuffer = buffer; 
      cout<<"func2:"<<p<<endl; ///doesn't work

      return zbuffer;
}

char *strhex(char *str)
{
     char buffer[500]="";
  char *pbuffer = buffer;
  int len = strlen( str );

     for( int i = 0; i < len ;i++ )
  {
  itoa(str[i],pbuffer,16);  
        pbuffer +=2;
     };

     *pbuffer = '\0'; 
     pbuffer=buffer;

     return pbuffer;
}

Edit: i'm using DEV C++ 4.9.9.2 on Windows

Upvotes: 0

Views: 1778

Answers (4)

codaddict
codaddict

Reputation: 454950

Adding to others answers:

You need not reset pbuffer to point to the start of the array and then return it's value:

pbuffer=buffer;
return pbuffer;

you can just say

return buffer;

the array name is also a pointer(pointer to the first element of the array.

Upvotes: 0

Mr. Mr.
Mr. Mr.

Reputation: 4285

it looks like it is working but the second cout in main is not printing out a value because you are returning an empty buffer.

Upvotes: 0

Chuck
Chuck

Reputation: 237010

Your entire code doesn't work. Both functions return pointers to local arrays, which don't point to anything valid after the function returns. That causes undefined behavior. Since the value of p is one of these invalid pointers, you can't depend on it to be anything at any particular time — that memory probably gets overwritten during func(). You need to either new[] and delete[] the appropriate memory or, preferably, use a proper C++ data structure like std::string.

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272467

One big problem here is that strhex is returning a pointer to a local variable (buffer[]). This variable goes out of scope at the end of the function, so the return value points at undefined memory contents that can be overwritten at any time.

Upvotes: 4

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