Why does this code allocate too much space?

[strack]

I have just begun learning pointer operations, and am attempting to create a function that will reverse a string. For some reason, however, revString is always allocated with an extra 4-5 bytes. The code is below, and I would appreciate anyone's help.

char *strrev(char *string)
{
	int n=strlen(string);
	char* revString=new char[n];

	while( n-- )
		*(revString+n) = *(string++);
	
	return revString;
}

 

[Jeffray]

You should add
revString[n]='\0';
to terminate your string before you reverse it.

 

[Jeffray]

And moreover, you should allocate one more byte for the null terminator.

 

[Zyrenthian]

I will make an assumption here and say it is a padding issue. Just for kicks try to rever the string "ABCD" and see if it works correctly. Also, I would do the new with n+1 and not n so you could add an extra character at the end of '\0' or 0 (zero). This may be your problem as well.

Matt

 

[tchouch]

Bad things can be with n = 0: new char[0] does not work (that is one of reasons to work witn n+1 (see Jeffray and Zyrenthian). Do it so:
char *strrev(char *string)
{
if(string == 0)
return (char*)NULL; //if string == NULL, strlen does not work
int n=strlen(string); //strlen returns size_t, not int -> by very-very big strings n < 0
char* revString=new char[n+1];

if(revString == NULL)
return (char*)NULL; //Not enough memory; for example, string hasn't 0 on end

revString[n] = 0; //or revString[n]='\0'; - it works by n= 0 too

while( n-- )
*(revString+n) = *(string++);

return revString;
}

 

[strack]

Thanks for your help. It was a null terminator problem.