atof.3

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3 代码 · 共 220 行

.\" SCCSID: @(#)atof.3	2.5	8/10/87
.TH atof 3 
.SH Name
atof, atoi, atol, strtol, strtoul, strtod \- convert ASCII to numbers
.SH Syntax
.nf
.B #include <math.h>
.PP
.B double atof(\fInptr\fP)
.B char *\fInptr\fP;
.PP
.B atoi(\fInptr\fP)
.B char *\fInptr\fP;
.PP
.B long atol(\fInptr\fP)
.B char *\fInptr\fP;
.PP
.B long strtol(\fInptr\fP, \fIeptr\fP, \fIbase\fP)
.B char *\fInptr\fP, **\fIeptr\fP;
.B int \fIbase\fP;
.PP
.B unsigned long strtoul(\fInptr\fP, \fIeptr\fP, \fIbase\fP)
.B char *\fInptr\fP, **\fIeptr\fP;
.B int \fIbase\fP;
.PP
.B double strtod (\fInptr\fP, \fIeptr\fP)
.B char *\fInptr\fP, **\fIeptr\fP;
.PP
.B unsigned long strtoul(\fInptr, eptr, base\fP)
.B char *\fInptr, **eptr\fP;
.B int \fIbase\fP;
.fi
.SH Description
.NXR "atof subroutine (standard C)"
.NXR "atoi subroutine"
.NXR "atol subroutine"
.NXR "strtol subroutine"
.NXR "strtod subroutine"
.NXR "atof subroutine (standard C) " "isalpha subroutine"
.NXR "isalpha subroutine" "atof subroutine (standard C)"
.NXR "ASCII string" "converting to numbers"
These functions convert a string pointed to by
.I nptr
to floating, integer, and long integer representation respectively.
The first unrecognized character ends the string.
.PP
The
.PN atof
function recognizes (in order), an optional string of spaces, 
an optional sign, a string of digits optionally containing a radix
character, an optional `e' or `E', and then an optionally signed integer.
.PP
The
.PN atoi
and
.PN atol
functions recognize (in order), an optional string of spaces, 
an optional sign, then a string of digits.
.PP
The
.PN strtol
function
returns as a long integer, the value represented by the 
character string
.I nstr.
The string is scanned up to the first character
inconsistent with the 
.I base.
Leading white-space
characters are ignored.
.PP
If the value of 
.I eptr
is not (char **) NULL, a pointer to the 
character terminating the scan is returned in
.I **eptr. 
If no integer can be formed, 
.I **eptr
is set to 
.I nstr ,
and zero is returned.
.PP
If \fIbase\fP is positive and not greater than 36,
it is used as the base for conversion.  After an
optional leading sign, leading zeros are ignored,
and 0x or 0X is ignored if \fIbase\fP is 16.
.PP
If \fIbase\fP is zero, the string itself determines 
the base thus:  After an optional leading sign, a
leading zero indicates octal conversion, and a 
leading 0x or 0X hexadecimal conversion.
Otherwise, decimal conversion is used.
.PP
Truncation from \fIlong\fR to \fIint\fR can take place upon 
assignment, or by an explicit cast.
.PP
The
.PN strtoul
function is the same as
.PN strtol
except that
.PN strtoul
returns, as an unsigned long integer, the value represented by the
character string
.I nstr.
.PP
The
.PN strtod
function returns as a double-precision floating point number,
the value represented by the character string pointed to by
.I nptr.
The string is scanned up to the first unrecognized character.
.PP
The
.PN strtod 
function recognizes an optional string of white-space characters,
as defined by \fIisspace\fP in
.PN ctype ,
then an optional sign, then a string of digits
optionally containing a radix character, then an optional \fIe\fR or \fIE\fR followed by an optional sign or space, followed by an integer.
.PP
If the value of
.I eptr
is not (char **)NULL, a pointer to the character
terminating the scan is returned in the location pointed to by
.I eptr.
If no number can be formed, \fI*eptr\fP is set to \fInptr\fP,
and zero is returned.
.PP
The radix character for
.PN atof
and
.PN strtod
is that defined by the last successful call to
.PN setlocale
category
.PN LC_NUMERIC .
If
.PN setlocale
category
.PN LC_NUMERIC
has not been called successfully, or if the radix character is not defined for a supported language, the radix character is defined as a period (.).
.SS International Environment
.IP LC_CTYPE 15
If this environment variable is set and valid,
.PN strtod
uses the international language database named in the definition to
determine character classification rules.
.IP LC_NUMERIC 15
If this environment is set and valid, 
.PN atof
and
.PN strtod
use the international language database named in the definition to
determine radix character rules.
.IP LANG 15
If this environment variable is set and valid 
.PN atof
and
.PN strtod
use the international language database named in the definition to
determine collation and character classification rules.  If
.PN LC_CTYPE
or 
.PN LC_NUMERIC 
is defined, their definition supercedes the definition of
LANG.
.SH Diagnostics
The
.PN atof
function returns HUGE
if an overflow occurs, and  a 0 value if an
underflow occurs, and sets
.I errno
to ERANGE.
HUGE is defined in
.PN <math.h>.
.PP
The 
.PN atoi 
function returns INT_MAX or INT_MIN (according to
the sign of the value) and sets 
.I errno 
to ERANGE, if the correct
value is outside the range of values that can be represented.
.PP
The 
.PN atol 
function returns LONG_MAX or LONG_MIN (according to
the sign of the value) and sets 
.I errno 
to ERANGE, if the correct
value is outside the range of values that can be represented.
.PP
The
.PN strtol
function returns LONG_MAX or LONG_MIN (according to the 
sign of the value) and sets
.I errno
to ERANGE, if the correct value is outside the 
range of values that can be represented.
.PP
The
.PN strtoul
function returns ULONG_MAX and sets
.I errno
to ERANGE, if the correct value is outside the range of values that can
be represented.
.PP
The
.PN strtod
function returns HUGE
(according to the sign of the value), and sets 
.I errno
to ERANGE if the correct value would cause overflow.  A 0 is returned and
.I errno
is set to ERANGE if the correct value would cause underflow.
.SH See Also
ctype(3), setlocale(3), scanf(3s), environ(5int)