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Topic: Maximum ATOI string (Read 1 time)previous topic - next topic

Pedro Ferrer

Jan 31, 2012, 09:31 am
Good morning

I would like to know which is the maximum string that I can convert to a number?

Eg:
Suppose that I have '999999999', I suppose that I can't convert to a number...

It's true?

Best regards
Pedro Ferrer

Nick Gammon

#1
Jan 31, 2012, 09:45 am
Well, how big is an int?
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

Pedro Ferrer

#2
Jan 31, 2012, 09:48 am
Hello

32768...
How can I convert '999999999' string to a numeric value at once?

Best regards

Nick Gammon

#3
Jan 31, 2012, 11:32 amLast Edit: Jan 31, 2012, 11:36 am by Nick Gammon Reason: 1
Hello.

Close, but no banana. 32767.

Quote
Suppose that I have '999999999', I suppose that I can't convert to a number...

You can always do things, but there is a cost ...

You can do it with BIG numbers:

http://arduino.cc/forum/index.php?topic=85692.0

It depends on what data type you want to end up with.

A "signed long" goes up to 2,147,483,647. That might work for you.

A "long long" goes up to 9,223,372,036,854,775,807.

(complaint) This is like pushing my way up through sludge. It took an hour to make this reply.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

PaulS

#4
Jan 31, 2012, 12:47 pm
You also need to use the correct function. atoi() converts strings to ints. atol() converts strings to longs. Both assume that the value is signed. There are not specific versions for unsigned values.

Pedro Ferrer

#5
Jan 31, 2012, 06:45 pm
Hello

Very interesting issue.

Best regards
Pedro Ferrer

dc42

#6
Jan 31, 2012, 06:54 pmLast Edit: Jan 31, 2012, 06:57 pm by dc42 Reason: 1
You can also use (from the AVR C library):

Quote

/**
The strtoul() function converts the string in \c nptr to an
unsigned long value.  The conversion is done according to the
given base, which must be between 2 and 36 inclusive, or be the
special value 0.

The string may begin with an arbitrary amount of white space (as
determined by isspace()) followed by a single optional \c '+' or \c '-'
sign.  If \c base is zero or 16, the string may then include a
\c "0x" prefix, and the number will be read in base 16; otherwise,
a zero base is taken as 10 (decimal) unless the next character is
\c '0', in which case it is taken as 8 (octal).

The remainder of the string is converted to an unsigned long value
in the obvious manner, stopping at the first character which is
not a valid digit in the given base.  (In bases above 10, the
letter \c 'A' in either upper or lower case represents 10, \c 'B'
represents 11, and so forth, with \c 'Z' representing 35.)

If \c endptr is not NULL, strtoul() stores the address of the first
invalid character in \c *endptr.  If there were no digits at all,
however, strtoul() stores the original value of \c nptr in \c
*endptr.  (Thus, if \c *nptr is not \c '\\0' but \c **endptr is \c '\\0'
on return, the entire string was valid.)

The strtoul() function return either the result of the conversion
or, if there was a leading minus sign, the negation of the result
of the conversion, unless the original (non-negated) value would
overflow; in the latter case, strtoul() returns ULONG_MAX, and \c
errno is set to \ref avr_errno "ERANGE".  If no conversion could
be performed, 0 is returned.
*/
extern unsigned long strtoul(const char *__nptr, char **__endptr, int __base);
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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