Character pointer problem :

[kulkarniamit]

#include<stdio.h>
#include<string.h>
#include<conio.h>

void strrevi(char *start,char *end)
{
     char *temp;
     if((!start || !end))
     return;
     for(;start<=end;start++,end--)
     {
//       printf("%c %c %c\n",*temp,*start,*end);

       temp=*start;
       *start=*end;
       *end=temp;     
  //     printf("%c %c %c\n",*temp,*start,*end);
       }
}



int main()
{
        char string[20]="some text";
        printf("%s\n",string); 
        strrevi(string,string+strlen(string)-1);
        printf("%s",string);
        getch();
        return 0;
}

The problem is in the strrevi function:
Why doesnt the program work properly if i use
char *temp in place of char temp and replace every instance of temp with *temp?
The commented lines may be uncommented for analysis purpose

[anduril462]

Making temp a char * doesn't actually give you a place to store the temporary character for your swap. Besides, even if you had it pointing to a valid character where you could store the data for the swap, you would need to dereference it. Here is how it would look if you properly used temp as a char * (note, this is NOT how I would recommend doing it, it's just for demo purposes).

void strrevi(char *start,char *end)
{
     char c;
     char *temp = &c;
     if((!start || !end))
     return;
     for(;start<=end;start++,end--)
     {
//       printf("%c %c %c\n",*temp,*start,*end);

       *temp=*start;
       *start=*end;
       *end=*temp;     
  //     printf("%c %c %c\n",*temp,*start,*end);
       }
}

Stick with "char temp;"

[quzah]

Why doesnt the program work properly if i use char *temp in place of char temp and replace every instance of temp with *temp?

It doesn't work because you have no understanding of pointers.

type var; /* a variable of type that holds a value */
type *ptr; /* a pointer to type, that holds an address of type variable */

ptr = &var; /* put the address of var into ptr as its value */
something = *ptr; /* get the value of what is at the address ptr holds */


Quzah.

[iMalc]

To perform a swap you need some temporary location to store the value you are swapping.
If you declare temp as a pointer then what's supposed to hold the actual value you are swapping around?

There's also no point in your ending condition being start<=end because you don't need to swap the middle character with itself. Just use start < end.

I also recommend you use the "end is one past the last character" approach as used by C++, which makes for more efficient code.

Edit: Damn 3 replies in as many minutes. At least we're saying pretty much exactly the same thing.