string inversion

[Lynch1975]

I would like to know the BEST way for a function, to invert a string received by pointer. Do you have code to propose? Number of parameters is free. Thanks

 

[mingis]

bool inverse(char *szStr)
{
char *pnts;
char *pntd;
char *buffer;
int ii;
bool retc=0;

ii=strlen(szStr);
buffer=new char[ii];
if(buffer!=NULL)
{
pntd=buffer;
pnts=szStr+ii;
while(pnts>szStr) *(pntd++)=*(--pnts);
*pntd=0;
strcpy(szStr, buffer);
retc=1;
delete buffer;
}

return(retc);
}

 

[Zyrenthian]

Just another approach

void inverse(char* buffer)
{
 int end = strlen(buffer)-1;
 int begin = 0;

 for(;begin<end;begin++,end--)
 {
   buffer[begin]^=buffer[end]^=buffer[begin]^=buffer[end];
 }
}

Matt

 

[lionelhill]

All goes to prove how starting with the right language and question produces the right solution! I followed a thread once on reversing a string without using any additional storage. Somehow that limitation forced everyone to think about methods that did use storage, and everyone was bursting into assembler and pushing things onto stacks and all that stuff. It was ages before anyone realised you just swap pairs of letters working your way towards the middle of the string.

(oh, if anyone wants an assembler version, I'll post it)

 

[Leibnitz]

Here is a very simple way to do it:

#include <iostream.h>
#include <string.h>

char *inverse( char *str )
{
	unsigned int len = strlen(str);
	char *cp = new char[len+1];
    int j = 0;
	
	for( int i = len - 1; i >= 0; i-- )
	{
		cp[j] = str[i];
		j++;
	}
	cp[j] = 0;
	strcpy( str, cp );

	delete cp;
	return str;
}


void main()
{
	char str[20] = {&quot;Hello world !&quot;};
	cout<<inverse(str)<<endl;
}

// output: ! dlrow olleH

 

[beetee]

Perhaps we should pay heed to lionelhill's sage advice:

void InvertInPlace(char *ptr)
{
char *start = ptr;
char *end = ptr;
while (*end)
++end;
int delta = end - start;
if (delta < 2)
return;
--end;
char *mid = &ptr[(delta + 1) / 2];
while (ptr < mid)
{
char temp = *end;
*end = *ptr;
*ptr = temp;
--end;
++ptr;
}
}

Newton