.TH ATOF 2
.SH NAME
atof, atoi, atol, charstod, strtod, strtol, strtoul \- convert text to numbers
.SH SYNOPSIS
.nf
.ta \w'\fLdouble 'u
.B
double	atof(char *nptr)
.PP
.B
int	atoi(char *nptr)
.PP
.B
long	atol(char *nptr)
.PP
.B
double	charstod(int (*f)(void *), void *a)
.PP
.B
double	strtod(char *nptr, char **rptr)
.PP
.B
long	strtol(char *nptr, char **rptr, int base)
.PP
.B
ulong	strtoul(char *nptr, char **rptr, int base)
.fi
.SH DESCRIPTION
.IR Atof ,
.IR atoi ,
and
.I atol
convert a string pointed to by
.I nptr
to floating, integer, and long integer
representation respectively.
The first unrecognized character ends the string.
Leading C escapes are understood, as in
.I strtol
with
.I base
zero.
.PP
.I Atof
recognizes an optional string of tabs and spaces,
then an optional sign, then
a string of digits optionally containing a decimal
point, then an optional 
.L e
or 
.L E
followed
by an optionally signed integer.
.PP
.I Atoi
and
.I atol
recognize an optional string of tabs and spaces,
then an optional sign, then a string of
decimal digits.
.PP
.I Strtod,
.I strtol,
and
.I strtoul,
behave similarly to 
.I atof,
and
.I atol
and, if
.I rptr
is not zero, set
.I *rptr
to point to the input character
immediately after the string converted.
.PP
.I Strtol
and
.I strtoul
interpret the digit string in the specified
.I base,
from 2 to 36,
each digit being less than the base.
Digits with value over 9 are represented by letters,
a-z or A-Z.
If
.I base
is 0, the input is interpreted as an integral constant in
the style of C (with no suffixed type indicators):
numbers are octal if they begin with
.LR 0 ,
hexadecimal if they begin with
.L 0x
or
.LR 0X ,
otherwise decimal.
.I Strtoul
does not recognize signs.
.PP
.I Charstod
interprets floating point numbers like
.IR atof ,
but it gets successive characters by calling
.BR (*\fIf\fP)(a) .
The last call to
.I f
terminates the scan, so it must have returned a character that
is not a legal continuation of a number.
Therefore, it may be necessary to back up the input stream one character
after calling
.IR charstod .
.SH SEE ALSO
.IR fscanf (2)
.SH DIAGNOSTICS
Zero is returned if the beginning of the input string is not
interpretable as a number; even in this case,
.I rptr
will be updated.
.SH BUGS
.I Atoi
and
.I atol
accept octal and hexadecimal numbers in the style of C,
contrary to the ANSI specification.
