How to find string contains a numeric value

[nishit.gupta]

Is their any fuction available in C++ that can determine that a string
contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"
Thnx

[Old Wolf]

On Apr 4, 4:01 pm, nishit.gu...@st .com wrote:

Is their any fuction available in C++ that can determine that a
string contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"

Try strtol(). If that gives an error then try strtod(). If that also
gives an error, then the string does not contain a numeric value.

[user923005]

On Apr 3, 9:01 pm, nishit.gu...@st .com wrote:

Is their any fuction available in C++ that can determine that a string
contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"

If you want a C++ solution, then post in news:comp.lang. c++

One answer to your question is to write a formal grammar for numbers
and then use the grammar to write a parser.

You could do it by hand in C by using fuctions:
isdigit()
isxdigit()
ispunct()
isalpha()
and a bit of logic.

P.S.
It's harder than it looks to get it right.

Just because something is a number doesn't mean you can read it in
either.

For example:
1.0e99999

[nishit.gupta]

Thanx fr reply but what does an error means......
strtol & strtod returns 0 on failure and my string can contains zero
too i.e. "0"
So how will i differentiate?? ?
and in strtol onre needs to give the base value, which i am not sure
it can be hex(16), decimal(10)???
Old Wolf wrote:

On Apr 4, 4:01 pm, nishit.gu...@st .com wrote:

Is their any fuction available in C++ that can determine that a
string contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"

Try strtol(). If that gives an error then try strtod(). If that also
gives an error, then the string does not contain a numeric value.

[Martin Ambuhl]

ni**********@st .com wrote:

Is their any fuction available in C++ that can determine that a string
contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"

If you tru;y want a C++ answer, you should post to a C++ newsgroup. We
don't do Fortran, COBOL, or Ada here, either.

If a C answer will suffice, have a look at the strto* family of
functions: strtod, strtof, strtold for floating point numbers;
strtoimax, strtol, strtoll, strtoul, strtoull, strtoumax for integral
numbers. In C these are prototyped in <stdlib.c>; for C++ the header
should be <cstdlib>, but check your C++ text to make sure. If you have
questions after checking your textbook (or implementation documentation)
ask in a C++ newsgroup, not here.

[Old Wolf]

On Apr 4, 4:10 pm, nishit.gu...@st .com wrote:

Thanx fr reply but what does an error means......
strtol & strtod returns 0 on failure and my string can contains zero
too i.e. "0"
So how will i differentiate?? ?
and in strtol onre needs to give the base value, which i am not sure
it can be hex(16), decimal(10)???

All your questions are answered by the documentation of strtol
and strtod. I tried a Google search and it found sufficient
documentation as the first hit for 'strtod'. You could also
look in the C Standard.

[Default User]

ni**********@st .com wrote:

Thanx fr reply but what does an error means......

Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or:
<http://www.caliburn.nl/topposting.html >

[user923005]

On Apr 3, 10:43 pm, "Old Wolf" <oldw...@inspir e.net.nzwrote:

On Apr 4, 4:10 pm, nishit.gu...@st .com wrote:

Thanx fr reply but what does an error means......
strtol & strtod returns 0 on failure and my string can contains zero
too i.e. "0"
So how will i differentiate?? ?
and in strtol onre needs to give the base value, which i am not sure
it can be hex(16), decimal(10)???

All your questions are answered by the documentation of strtol
and strtod. I tried a Google search and it found sufficient
documentation as the first hit for 'strtod'. You could also
look in the C Standard.

Neither strtol() nor strtod() is capable of deciding whether a string
contains a numeric value.
They would be jim-dandy for turning a string into a numeric value,
once it has been determined that the string does contain one of the
proper format.

[John Bode]

On Apr 3, 11:01 pm, nishit.gu...@st .com wrote:

Is their any fuction available in C++ that can determine that a string
contains a numeric value.
The value cabn be in hex, int, float. i.e. "1256" , "123.566" ,
"0xffff"
Thnx

AFAIK, there is no *single* function that can recognize a numeric
string in any format. You can go one of two ways here: you can use a
combination of standard library functions (strtol(), strtod(),
strchr(), etc.) to attempt to convert the string to a numeric value,
and then check for any unconverted characters. The general algorithm
would be:

Strip leading whitespace
If the first character is '0' then
If the second character is 'x' or 'X' then
Convert the string using strtol(string, &check, 16)
where check is a pointer to a character
If *check is 0 or whitespace then
the string is an integer in hex format
Else
the string is not numeric
Else
Convert the string using strtol(string, &check, 8)
If *check is 0 or whitespace
the string is an integer in octal format
Else
the string is not numeric
End If
Else
If strpbrk(string, ".eE") is not null then
Convert the string using strtod(string, &check)
If *check is whitespace or 0 then
the string is a float in decimal
Else
the string is not numeric
End If
Else
Convert the string using strtol(string, &check, 10)
If *check is whitespace or 0 then
the string is an integer in decimal
Else
the string is not numeric
End If
End If
End If

Alternately, you can build a finite state machine that will scan the
string character by character; if the machine is in an accepting state
after scanning the whole string, then the string is numeric. This
isn't as straightforward a method as the above, and it can involve
quite a bit more work. The tradeoff is that you can accept strings in
any format you like, such as "1,234,567" , where the method above
won't.

FSMs can get *very* tedious to write if you have a lot of states.
There are tools like lex or flex that will generate FSMs based on
rules you specify, but they take a little time to learn, and they're
not universally available. However, if you decide to expand your
rules for a valid numeric string, it's a helluva lot easier to edit
the specification file for lex than to try to edit the FSM code
itself.

[Old Wolf]

On Apr 5, 9:01 am, "user923005 " <dcor...@connx. comwrote:

Neither strtol() nor strtod() is capable of deciding whether a string
contains a numeric value.

C & V ?