C ++ cout指针

Question

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

Answer 1

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.

Answer 2

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 .

Answer 3

看起来好像正在工作，但是main中的第二个cout没有打印出值，因为您正在返回一个空缓冲区。

Answer 4

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.