size_t and null characters...

[Yoshima]

Hello,

I just got myself a bit confused over size_t... I have written the following function to extract the last four characters of a date to get the year:

string yearSet(string fullDate)
{
	char yearBuf[4];
	size_t yearLength;
	
	yearLength = fullDate.copy(yearBuf,4,6);
	yearBuf[yearLength] = '\0';
	return yearBuf;
}

I assume that the code...
fullDate.copy(yearBuf,4,6)
... copies the last four char from fullDate into yearBuf....

... what does this make yearLength? Is it's value 4? Or is it the 4 characters?

Thanks for any help...

[Athar]

Don't assume, check:
http://www.cplusplus.com/reference/string/string/copy/

[Yoshima]

ok... so fullDate.copy will give four characters and the yearLength will be assigned to the number of characters? Does this mean the null character is assigned to the 4th element in yearBuf?

Thanks.

[Athar]

The function does not append a null character after the content copied.

[Duthomhas]

Why mess with char[] arrays at all?
Use the substr() member function:
http://www.cplusplus.com/reference/string/string/substr/

[Yoshima]

ok, so it does become the 4th character... thanks for the help... I think I understand it better now..

[Yoshima]

thanks Duoas... I think I'll try out the substr()... seems simpler...

[moorecm]

Does this mean the null character is assigned to the 4th element in yearBuf?
[...]
ok, so it does become the 4th character... thanks for the help... I think I understand it better now..

No, no. I think everybody has skipped your question. Although std::string is a much better solution, I'll point out a flaw and answer your question.

string yearSet(string fullDate)
{
	char yearBuf[4];                         // allocate 4 characters (indexes 0-3)
	size_t yearLength;
	
	yearLength = fullDate.copy(yearBuf,4,6); // copy 4 characters into yearBuf
                                                 // and set yearLength to 4
	yearBuf[yearLength] = '\0';              // write a null to the 5th character--beyond the end of
                                                 // yearBuf because array indexes start at 0
	return yearBuf;
}

To fix the buffer overrun, you would want to allocate 5 characters: 4 for the year and 1 for the null.