Thread: recursive function question

Hi,

I was trying to see why does this code works , i found it at another website. It is a function to reverse a string

Code:

char* reverse_str(char* s)
{
	char* reverse = malloc(1);
	//char* reverse;

	int i;

	if(*s != '\0')
		reverse = reverse_str(s+1);

	i = strlen(s) - 1;

	if (i >= 0)
		reverse[i] = s[0];

	return reverse;
}

my question is , why does this code works? because I see that each recursive call to the function assigns just one memory location to the "char *reverse " variable and then when the recursive calls end , the variable "char *recursive" is treated like if it was assigned more than one location.

sorry for my english.

Define "works". This code is wrong.... horribly wrong.

Originally Posted by hkl01

the code reverse all strings , i can't understand how the recursive memory assignment with malloc(1) creates consecutive memory locations in the same variable

It doesn't. It's a waste of memory that is allocated and goes nowhere.

Are you trying to reverse a character? Well, that's certainly nice.

You could reverse a string very easily using 1 for loop.

Code:

void reverse(char str[])
{
int i;
for(i = strlen(str); i > 0; i--)
printf("%c", str[i]);
}

int main(void)
{
char str[10] = "HelloWorld";
reverse(str);

return 0;
}

That's not much better -- you're printing the NULL and ignoring the first character in the string. Plus strlen() returns a size_t. And it's not indented.

Try something more along the lines of this: (codeformed)

Code:

#include <stdio.h>  /* for putchar() */
#include <string.h>  /* for strlen() */

void print_string_reverse(const char *str) {
    size_t x;

    for(x = strlen(str); x > 0; x --) {
        putchar(str[x - 1]);
    }
}

I don't think that was the OP's original question anyway . . . .