String reverse using pointers

Question

I'm trying to reverse a string using pointers.When i try to print the reversed string instead of getting DCBA i'm getting out only as BA?Can anyone help me on this?

#include<stdio.h>
void reverse(char *);
void main()
{
  char str[5] = "ABCD";
  reverse(str);
}

void reverse(char *str)
{
  char *rev_str = str;
  char temp;
  while(*str)
      str++;
  --str;

  while(rev_str < str)
  {
      temp = *rev_str;
      *rev_str = *str;
      *str = temp;   
      rev_str++;      
      str--;
  }
  printf("reversed string is %s",str);
}

Think about what str is pointing to at the time you call printf — David Gelhar
– David Gelhar, Commented Apr 24, 2012 at 17:03
possible duplicate of How to reverse a string in place in c using pointers? — Bo Persson
– Bo Persson, Commented Apr 24, 2012 at 17:10

Charles Salvia · Accepted Answer · 2012-04-24 17:04:12Z

2

You're losing your pointer to the beginning of the string, so when you print it out you're not starting from the first character, because str no longer points to the first character. Just put in a placeholder variable to keep a pointer to the beginning of the string.

void reverse(char *str)
{
  char *begin = str; /* Keeps a pointer to the beginning of str */
  char *rev_str = str;
  char temp;
  while(*str)
      str++;
  --str;

  while(rev_str < str)
  {
      temp = *rev_str;
      *rev_str = *str;
      *str = temp;   
      rev_str++;      
      str--;
  }
  printf("reversed string is %s\n", begin);
}

answered Apr 24, 2012 at 17:04

Charles Salvia

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SK17 · Accepted Answer · 2022-01-14 12:55:35Z

0

char* strrev(chr* src)
{      
       char* dest
       int len=0 ;    //calculate length of the src string
       int index=0 ;  // index for dest (output) string
       int rindex=0; //Index to be counted from end toward beginning of src string

       //Calculate length of the string
       //Keep iterating till it reaches to null char '\0'

       while(*(src+len) != '\0')
       { len++ }

       //pointing rindex at the last character of src string 
       rindex=len-1;

       
       //Start copying from last char of src string at first index of dest array
       // Copying second last char of src string at second index of dest array and so on ..


       while(rindex > =0)
       {
           *(dest+index) = *(src + rindex)
            index++;
            rindex--;
       }

   // Finally covert array of char into string , by inserting a null char at the end of dest array

      *(dest+index) = '\0';


return dest;
}

edited Jan 14, 2022 at 12:55

answered Sep 3, 2018 at 8:15

SK17

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1 Comment

Alex Riabov Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

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