NAME
strtol
, strtoll
,
strtoimax
, strtoq
—
convert string value to a long, long
long, intmax_t or quad_t integer
LIBRARY
library “libc”
SYNOPSIS
#include
<stdlib.h>
#include <limits.h>
long int
strtol
(const
char * restrict nptr,
char ** restrict endptr,
int base);
long long int
strtoll
(const
char * restrict nptr,
char ** restrict endptr,
int base);
#include <inttypes.h>
intmax_t
strtoimax
(const
char * restrict nptr,
char ** restrict endptr,
int base);
#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>
quad_t
strtoq
(const
char * restrict nptr,
char ** restrict endptr,
int base);
DESCRIPTION
Thestrtol
()
function converts the string in nptr to a
long int value. The
strtoll
()
function converts the string in nptr to a
long long int value. The
strtoimax
()
function converts the string in nptr to an
intmax_t value. The
strtoq
()
function converts the string in nptr to a
quad_t 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(3)) followed by a single optional
‘+
’ or
‘-
’ sign. If
base is zero or 16, the string may then include a
‘0x
’ or
‘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
‘0
’, in which case it is taken as 8
(octal).
The remainder of the string is converted to an appropriate 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
‘A
’ in either upper or lower case
represents 10, ‘B
’ represents 11, and
so forth, with ‘Z
’ representing
35.)
If endptr is non-nil, the functions store
the address of the first invalid character in *endptr.
If there were no digits at all, however, the functions store the original
value of nptr in *endptr. (Thus,
if *nptr is not
‘\0
’ but
**endptr is ‘\0
’
on return, the entire string was valid.)
RETURN VALUES
The strtol
() function returns the result
of the conversion, unless the value would underflow or overflow. If an
underflow occurs, strtol
() returns
LONG_MIN
, strtoll
() returns
LLONG_MIN
, and strtoimax
()
returns INTMAX_MIN
. If an overflow occurs,
strtol
() returns LONG_MAX
,
strtoll
() returns LLONG_MAX
,
and strtoimax
() returns
INTMAX_MAX
. In these cases,
errno is set to ERANGE
. If the
base argument is not supported then
errno is set to EINVAL
and the
functions return 0.
If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.
EXAMPLES
Because the return value of strtol
()
cannot be used unambiguously to detect an error, errno
is left unchanged after a successful call. To ensure that a string is a
valid number (i.e., in range and containing no trailing characters), clear
errno beforehand explicitly, then check it
afterwards:
char *ep; long lval; ... errno = 0; lval = strtol(buf, &ep, 10); if (ep == buf) goto not_a_number; if (*ep != '\0') goto trailing_garbage; if (errno) { assert(errno == ERANGE); assert(lval == LONG_MAX || lval == LONG_MIN); goto out_of_range; }
This example will accept “12” but not “12foo” or “12\n”. If trailing whitespace is acceptable, further checks must be done on *ep; alternately, use sscanf(3).
If strtol
() is being used instead of
atoi(3), error checking is further complicated because the desired
return value is an int
rather than a
long
; however, on some architectures integers and
long integers are the same size. Thus the following is necessary:
char *ep; int ival; long lval; ... errno = 0; lval = strtol(buf, &ep, 10); if (ep == buf) goto not_a_number; if (*ep != '\0') goto trailing_garbage; if (errno == ERANGE || lval < INT_MIN || INT_MAX < lval) goto out_of_range; assert(errno == 0); assert(INT_MIN <= lval); assert(lval <= INT_MAX); ival = lval;
ERRORS
- [
EINVAL
] - The base is not between 2 and 36 and does not contain the special value 0.
- [
ERANGE
] - The given string was out of range; the value converted has been clamped.
SEE ALSO
atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtou(3), strtoul(3), strtoull(3), strtoumax(3)
STANDARDS
The strtol
() function conforms to
ANSI X3.159-1989 (“ANSI C89”).
The strtoll
() and
strtoimax
() functions conform to
ISO/IEC 9899:1999
(“ISO C99”).
The strtoq
() function is a
BSD legacy function equivalent to
strtoll
() and should not be used in a new code.
BUGS
Ignores the current locale.