STRTOL(3) | Library Functions Manual | STRTOL(3) |
strtol
, strtoll
,
strtoimax
, strtoq
—
#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);
strtol
() 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.)
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.
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;
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.
November 4, 2016 | NetBSD 9.2 |