C++ String Terminator

[sake]

Hi, : )
I know that C++ Strings are not terminated with a NULL terminator like C strings, so what are they terminated with? I'm making a calculator currently that parses an expression by separating the numbers and operators and putting them in a list with accordance to the order of operations. When I parse the expression, I go through the string with a for loop, and test each character against a switch statement. If the character is a number (0-9), then its added to a separate string, when the switch reaches an operator, it dumps the separate string into the list and starts over. The problem is getting the last number, because there is no operator after it. Think "22+33", there is nothing after 33 to test the switch against, and thus, the string never gets dumped into the list. Any way I can test for the end of the string, or anyone got a different idea to go about this whole process?

Thanks,
Austen

[JosAH]

Hi, : )
I know that C++ Strings are not terminated with a NULL terminator like C strings, so what are they terminated with? I'm making a calculator currently that parses an expression by separating the numbers and operators and putting them in a list with accordance to the order of operations. When I parse the expression, I go through the string with a for loop, and test each character against a switch statement. If the character is a number (0-9), then its added to a separate string, when the switch reaches an operator, it dumps the separate string into the list and starts over. The problem is getting the last number, because there is no operator after it. Think "22+33", there is nothing after 33 to test the switch against, and thus, the string never gets dumped into the list. Any way I can test for the end of the string, or anyone got a different idea to go about this whole process?

Thanks,
Austen

If you need a '\0' character at the end of the string you can even mimic it:

for (int i= 0, n= your_string.size(); i <= n; i++) {
   char chr= (i == n)?'\0':your_string[i];
   // your code here 
}

You can even append a literal '\0' char to your_string and remove it again when
you're done with parsing the string, but I prefer the approach above.

kind regards,

Jos

[ayan4u]

even with c++ strings thr is a null termination....cause u can iterate thru the string makng a condition tht u continue unless u meet the NULL...

i.e.,

string expression ="Am i worthy enough":
int i=0;
while(expression[i]!=NULL)
{ code...
i++;}
 

[JosAH]

even with c++ strings thr is a null termination....cause u can iterate thru the string makng a condition tht u continue unless u meet the NULL...

That is not true; try the at() member function instead of operator[] and see for
yourself. (at() performs a range check, operator[] simply goes berzerk).

kind regards,

Jos

[sake]

That is not true; try the at() member function instead of operator[] and see for
yourself. (at() performs a range check, operator[] simply goes berzerk).

kind regards,

Jos

Yeah, I've tried testing for a NULL terminator, but it didn't work. I guess this has to do with not having to define the space required for a string. I think the easiest way to get this done is to just manually append a '\0' to the end of the string.

Thanks Josah and Ayan : )

[weaknessforcats]

You test for end of a C++ string by using an iterator:

string::iterator itr;

itr = str.begin();

while (itr != str.end())
{
//string hasn't ended
++itr;
}
//string has ended.

STL uses iterators everywhere.

The null terminator is for a C string. Try not to make C++ into C.

[ayan4u]

Yeah, I've tried testing for a NULL terminator, but it didn't work. I guess this has to do with not having to define the space required for a string. I think the easiest way to get this done is to just manually append a '\0' to the end of the string.

Thanks Josah and Ayan : )

u are saying tht running a loop around the string object till u encounter /0 isn't operating...i know the operator [] is sumthing bizzare with c++ strings...but the above said process does work...and i checkd....

u can as well use iterators....they r friendly....but i just responded as i saw in one f my pros tht '\0' chkn in strings is workn....

[JosAH]

u are saying tht running a loop around the string object till u encounter /0 isn't operating...i know the operator [] is sumthing bizzare with c++ strings...but the above said process does work...and i checkd....

u can as well use iterators....they r friendly....but i just responded as i saw in one f my pros tht '\0' chkn in strings is workn....

There is nothing bezarre about the operator[], it is simply overloaded. There
is no '\0' character following the other characters in a string. Read chapter 20,
page 586 of Stroustrup's "The C++ Programming Language, edition III or the
documentation of any conforming STL. If there *does* happen to be a trailing
'\0' character at position string.size() that'd be just serendipity, i.e. undefined.

kind regards,

Jos

[weaknessforcats]

If you insist on using a null terminator check like the string objkect is a C string then call the method that makes the string object appear as a const C string:

if (str.c_str()[i] == '\0')
{
    //string has ended
}
 

[JosAH]

If you insist on using a null terminator check like the string objkect is a C string then call the method that makes the string object appear as a const C string:

if (str.c_str()[i] == '\0')
{
    //string has ended
}
 

If you'd put that in a loop it would be extremely inefficient, i.e. the c_str()
function cannot assume that the string data had remained the same between
two c_str() invocations so it would allocate another buffer again for a copy
of the relevant string data.

kind regards,

Jos

[sake]

I'm not insisting to use a Null terminator, I'm just trying to find the best way. The iterator seems to work. Thanks alot for everyone's help :-)

[sake]

Sorry about double posting, but I have just one more question. I didn't think it needed a new thread.
I've tried using the clear() method, but it doesnt seem to get rid of verything in a string. I shtere any other way to surely eradicate everything in a string? Like make all of the characters it contains blank. I've also tried doing that manually within a for loop, setting every element to: '' (two single quotes), "" (two double quotes), and NULL. None of these worked, however. Specifically, my problem is when I convert my string to a C string and then convert that into a number. Because the string storing the number is reused, a larger number preceding the new number will not get overwritten (Think "235+3", when parsed, "3" will become "335". Or, "3"+"35", because only the "2" in the previous string was overwritten. Any ideas?
Thanks again,
Austen

[ayan4u]

wht dnt u use erase....

string s ="abcd is 1234";

s.erase(4,2);

this will make s = "abcds 1234";

s.erase(2);

this will make s="ab";

s.erase(); // this erases the entire string

or u can use iterators...

s.erase(iterator begin, iterator end);

s.erase(iterator pos);


now as far as detecting charecters as numbers...

use isdigit() or isalpha() included in ctype.h....then use the corresponding ASCII value if you find it to be a digit...