strtol, strtoll, strtoq — convert a string to a long integer
#include <stdlib.h>
long
int strtol( |
const char * | nptr, |
char ** | endptr, | |
int | base) ; |
long
long int strtoll( |
const char * | nptr, |
char ** | endptr, | |
int | base) ; |
The strtol
() function
converts the initial part of the string in nptr
to a long integer value
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' 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 a long int 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 not
NULL, strtol
() stores the
address of the first invalid character in *endptr
. If there were no
digits at all, strtol
() stores
the original value of nptr
in *endptr
(and returns 0). In
particular, if *nptr
is not `\0' but
**endptr
is `\0' on
return, the entire string is valid.
The strtoll
() function works
just like the strtol
() function
but returns a long long integer value.
The strtol
() function
returns the result of the conversion, unless the value would
underflow or overflow. If an underflow occurs, strtol
() returns LONG_MIN. If an overflow
occurs, strtol
() returns
LONG_MAX. In both cases, errno
is set to ERANGE. Precisely the same holds for strtoll
() (with LLONG_MIN and LLONG_MAX
instead of LONG_MIN and LONG_MAX).
(not in C99) The given base
contains an
unsupported value.
The resulting value was out of range.
The implementation may also set errno
to EINVAL in case no conversion was performed
(no digits seen, and 0 returned).
Since strtol
() can
legitimately return 0, LONG_MAX, or LONG_MIN (LLONG_MAX or
LLONG_MIN for strtoll
()) on
both success and failure, the calling program should set
errno
to 0 before the call, and
then determine if an error occurred by checking whether
errno
has a non-zero value after
the call.
In locales other than the "C" locale, other strings may also be accepted. (For example, the thousands separator of the current locale may be supported.)
BSD also has
quad_t strtoq
(const char *nptr
,char **endptr
,int base
);
with completely analogous definition. Depending on the
wordsize of the current architecture, this may be equivalent
to strtoll
() or to strtol
().
strtol
() conforms to SVr4,
4.3BSD, C89, C99 and POSIX.1-2001, and strtoll
() to C99 and POSIX.1-2001.
The program shown below demonstrates the use of
strtol
(). The first command
line argument specifies a string from which strtol
() should parse a number. The second
(optional) argument specifies the base to be used for the
conversion. (This argument is converted to numeric form using
atoi(3), a function that
performs no error checking and has a simpler interface than
strtol
().) Some examples of the
results produced by this program are the following:
$ ./a.out 123 strtol() returned 123 $ ./a.out ' 123' strtol() returned 123 $ ./a.out 123abc strtol() returned 123 Further characters after number: abc $ ./a.out 123abc 55 strtol: Invalid argument $ ./a.out '' No digits were found $ ./a.out 4000000000 strtol: Numerical result out of range
The source code of the program is as follows:
#include <stdlib.h> #include <limits.h> #include <stdio.h> #include <errno.h> int main(int argc, char *argv[]) { int base; char *endptr, *str; long val; if (argc < 2) { fprintf(stderr, "Usage: %s str [base]\n", argv[0]); exit(EXIT_FAILURE); } str = argv[1]; base = (argc > 2) ? atoi(argv[2]) : 10; errno = 0; /* To distinguish success/failure after call */ val = strtol(str, &endptr, base); /* Check for various possible errors */ if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN)) || (errno != 0 && val == 0)) { perror("strtol"); exit(EXIT_FAILURE); } if (endptr == str) { fprintf(stderr, "No digits were found\n"); exit(EXIT_FAILURE); } /* If we got here, strtol() successfully parsed a number */ printf("strtol() returned %ld\n", val); if (*endptr != '\0') /* Not necessarily an error... */ printf("Further characters after number: %s\n", endptr); exit(EXIT_SUCCESS); }
atof(3), atoi(3), atol(3), strtod(3), strtoul(3)
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