How to reverse a string into a empty string recursively in c

Question

I have this problem with an assignment. Im supposed to reverse a string recursively into another empty string. The thing is that the function modifies the source string which it is not supposed to do, just to copy the string backwards to the destination string. I don't understand why this is happening...

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

void
invert(const char *src, char dest[])
{
    if(*src=='\0')
        return;
    else
    {
        invert(src+1, dest);
        dest[strlen(src)-1]=*src;
    }
}

int main(int argc, const char * argv[])
{
    char dest[]="";
    char src[]="";
    printf("write a word: \n");
    scanf("%s", src);
    invert(src, dest);
    dest[strlen(src)]='\0';
    printf("the inversion of the word is: %s\n", dest);
    return 0;
}

For example: writing Ulysses => sessesU and writing Jones => seesJ\377

@dbeer Don't do that. The homework tag is deprecated.

user529758
– user529758

2012-11-28 21:54:23 +00:00
Commented Nov 28, 2012 at 21:54 — user529758
– user529758, Commented Nov 28, 2012 at 21:54
Sorry, I somehow missed that.

dbeer
– dbeer

2012-11-28 21:54:48 +00:00
Commented Nov 28, 2012 at 21:54 — dbeer
– dbeer, Commented Nov 28, 2012 at 21:54

dreamcrash · Accepted Answer · 2012-11-28 21:59:16Z

4

The problem is here:

char dest[]="";
char src[]="";

you're allocating two times one character - the variables are probably next to each other on the stack, that's why writing to the one erroneously overwrites the contents of another.

You should allocate sufficient storage for the strings. If you're sure the input of your program will never exceed for example 1023 bytes, then two 1k buffers should be good:

char src[1024], dest[1024];

edited Nov 28, 2012 at 21:59

dreamcrash

52.5k26 gold badges114 silver badges138 bronze badges

answered Nov 28, 2012 at 21:50

user529758

Sign up to request clarification or add additional context in comments.

4 Comments

bph Over a year ago

or perhaps dest and scr point to the same address as compilers may optimise assignment to identical string literals to conserve memory (see stackoverflow.com/questions/11399682/…)

user529758 Over a year ago

@Hiett In no way. Since dest and src are declared as arrays, and not pointers, they're stack-allocated and pre-filled with the appropriate string. Your statement would be true if the declaration was const char *src = "", *dest = "";.

bph Over a year ago

@Carbonic thanks for the explanation - so char dest[]="" is not a string literal with static storage, its a local array?

bph Over a year ago

have just found this which explained things [stackoverflow.com/questions/2036096/… - bit of a C gotcha if you don't know whats going on...

Collectives™ on Stack Overflow

How to reverse a string into a empty string recursively in c

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related