CODEWITHSUNDEEP
iphonensstringreverse
vivianaranha
vivianaranha

Reputation: 2781

How to reverse a string without allocating memory

I was asked this question on how to reverse a string without allocating memory. Any takers?

Upvotes: 0

Views: 894

Answers (3)

vivianaranha
vivianaranha

Reputation: 2781

void reverseStringBetter(char* str)
{
    int i, j;
    i=j=0;

    j=strlen(str)1;
    for (i=0; i<j; i++, j-)
    {
        str[i] ^= str[j] ;
        str[j] ^= str[i] ;
        str[i] ^= str[j] ;
    }
}

Upvotes: 1

Kekoa
Kekoa

Reputation: 28240

It is not possible with NSString since they are immutable and the only way is to create a new string.

Though this might not be what you are looking for, you can convert the NSString to a normal c-string, and edit that in-place. You are still allocating memory, but you'll at least get half of what you want by being able to modify the string in place.

I'm not sure what your use case is for not wanting to allocate memory, or if this is simply a hypothetical.

Upvotes: 0

rob mayoff
rob mayoff

Reputation: 385600

You cannot reverse an NSString, with or without allocating memory, because an NSString is immutable.

You cannot reverse an NSMutableString in place without allocating memory, because the only methods that NSMutableString provides to replace its contents require the new characters to be specified in an NSString, which you would have to allocate.

CFMutableString has the same “problem”.

Upvotes: 4

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