strtol(3) Library Functions Manual strtol(3)
NAME
strtol, strtoll, strtoq - convert a string to a long integer
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
long strtol(const char *restrict nptr,
char **_Nullable restrict endptr, int base);
long long strtoll(const char *restrict nptr,
char **_Nullable restrict endptr, int base);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strtoll():
_ISOC99_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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" 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 a long 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 uppercase
or lowercase represents 10, 'B' represents 11, and so forth, with 'Z'
representing 35.)
If endptr is not NULL, and the base is supported, 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() re-
turns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In
both cases, errno is set to ERANGE. Precisely the same holds for str-
toll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).
ERRORS
This function does not modify errno on success.
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).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│ strtol(), strtoll(), strtoq() │ Thread safety │ MT-Safe locale │
└─────────────────────────────────────┴───────────────┴────────────────┘
VERSIONS
According to POSIX.1, in locales other than "C" and "POSIX", these func-
tions may accept other, implementation-defined numeric strings.
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().
STANDARDS
C11, POSIX.1-2008.
HISTORY
strtol()
POSIX.1-2001, C89, SVr4, 4.3BSD.
strtoll()
POSIX.1-2001, C99.
CAVEATS
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 == ERANGE after the
call.
If the base needs to be tested, it should be tested in a call where the
string is known to succeed. Otherwise, it's impossible to portably dif-
ferentiate the errors.
errno = 0;
strtol("0", NULL, base);
if (errno == EINVAL)
goto unsupported_base;
EXAMPLES
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 sim-
pler 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
Program source
#include <errno.h>
#include <stdio.h>
#include <stdlib.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]) : 0;
errno = 0; /* To distinguish success/failure after call */
strtol("0", NULL, base);
if (errno == EINVAL) {
perror("strtol");
exit(EXIT_FAILURE);
}
errno = 0; /* To distinguish success/failure after call */
val = strtol(str, &endptr, base);
/* Check for various possible errors. */
if (errno == ERANGE) {
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 ALSO
atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3)
Linux man-pages 6.9.1 2024-06-16 strtol(3)
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