How do you reverse a given string in c plus plus?

Answer 1

The simplest way is to use the strrev() function.

To manually reverse a string, point to the first and last characters, swap their values, then move the pointers one character towards the middle of the string and repeat. If the pointers point to the same character or pass each other, the string is reversed.

The following is an example implementation. The function only process the given string when the string has 2 or more characters and a null-terminator is found within the first lencharacters.

#include

#include

using namespace std;

void strRev( char * input, size_t len )

{

// Minimum length is three (2 characters, 1 null-terminator).

const int min = 3;

if( len < min )

return;

// Locate the left-most character.

char * l = input;

// Locate the null-terminator:

char * n = l;

while( *n && n < l+len )

++n;

if( *n )

return; // null-terminator not found.

// Confirm the length (ignoring null-terminator).

if( n-l < min-1 )

return;

// Locate the right-most character (left of null-terminator)

char * r = n-1;

// Repeat while right pointer is greater than left pointer.

while( r>l )

{

*n = *l; // use the null-terminator to assist the swap.

*l++ = *r; // change left value and advance pointer.

*r-- = *n; // change right value and retreat pointer.

}

// Restore the null terminator.

*n = 0;

}

int main()

{

// Safest method of entering a string:

string input = "";

printf( "Enter a string: ");

getline( cin, input );

// Determine length of input + null-terminator.

size_t len = input.length() + 1;

// Convert string to a null-terminated string.

char * p = ( char * ) calloc( len, sizeof( char ));

memcpy( p, input.data(), input.length() );

// Reverse the string.

strRev( p, len );

printf( "Reversed: %s\n", p );

// Release memory.

free( p );

return( 0 );

}