How do you swap two strings in c plus plus?

Answer 1

The most efficient way to swap strings is to point at them, and swap the pointers. Swapping the actual strings is problematic if the strings are of unequal length but impossible when they are also statically allocated. Dynamic strings can always be physically swapped, however it's highly inefficient. If it really must be done, then use a built-in method such as string::swap(). Otherwise just use string pointers and swap the pointers, never the strings themselves.

The following example shows how both techniques can be used on statically allocated strings. Example output is show below.

#include <iostream>

using namespace std;

void SwapPointers(char ** pp1, char ** pp2 )

{

cout<<"\nSwapping pointers:"<<endl;

char * t = *pp1;

*pp1 = *pp2;

*pp2 = t;

}

void SwapStatics(char * String1, char * String2, size_t len)

{

cout<<"\nSwapping static strings:"<<endl;

while(len--) String1[len]^=String2[len]^=String1[len]^=String2[len];

}

int main()

{

char s1[] = "one ";

char s2[] = "two ";

char s3[] = "three ";

// Note that the output statements before and after

// swapping are exactly the same, proving the strings

// have really swapped.

cout<<"Original strings:"<<endl;

cout<<s1<<s2<<s3<<endl;

SwapStatics(s1,s2,sizeof(s1));

cout<<s1<<s2<<s3<<endl;

cout<<endl;

// We cannot swap s3 with either s1 or s2, because

// s1 and s2 don't have the space to accomodate s3.

// However, we can use pointers instead:

char * p1 = s1;

char * p2 = s2;

char * p3 = s3;

// Again, note that the output statements are the

// same before and after swapping, proving the

// pointers have swapped.

cout<<"Original pointers:"<<endl;

cout<<p1<<p2<<p3<<endl;

SwapPointers(&p1,&p3);

cout<<p1<<p2<<p3<<endl;

cout<<endl;

// Just to prove the strings didn't swap...

cout<<"The strings have not swapped:"<<endl;

cout<<s1<<s2<<s3<<endl;

cout<<endl;

return(0);

}

Output:

Original strings:

one two three

Swapping static strings:

two one three

Original pointers:

two one three

Swapping pointers:

three one two

The strings have not swapped:

two one three

Answer 2

//Using string.swap function to swap two strings
#include
#include
#include
using namespace std;
int main()
{
string frst("one");
string scnd("two");
cout<<" Before swap:\n First: "<frst.swap(scnd);
cout<<"\n After swap:\n First: "<getch();
return 0;
}

Answer 3

Except in certain limiting cases, you cannot swap two strings without using temporary variables.

Case one is where the two strings are actually pointers to strings. In that case, you can swap the pointer values, effectively swapping the strings.

Case two is where the two strings are not pointers, andthe strings have the same length. However, you need an index or pointer to walk through the strings, so, if that counts as a temporary variable, then case two is out.