STRTOL(3) Linux Programmer's Manual STRTOL(3)NAME
strtol, strtoll, strtoq - convert a string to a long integer
SYNOPSIS
#include <stdlib.h>
long int
strtol(const char *nptr, char **endptr, int base);
long long int
strtoll(const char *nptr, char **endptr, int base);
DESCRIPTION
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 deter‐
mined 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.
RETURN 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).
ERRORS
EINVAL (not in C99) The given base contains an unsupported value.
ERANGE 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).
NOTES
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 deter‐
mine 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 str‐
tol().
CONFORMING TOstrtol() conforms to SVr4, 4.3BSD, C99 and POSIX.1-2001, and strtoll()
to C99 and POSIX.1-2001.
EXAMPLE
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 pro‐
duced 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);
}
SEE ALSOatof(3), atoi(3), atol(3), strtod(3), strtoul(3)GNU 2002-05-30 STRTOL(3)
