strtol(3) - Linux manual page (original) (raw)
strtol(3) Library Functions Manual strtol(3)
NAME top
strtol, strtoll, strtoq - convert a string to a long integerLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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_SOURCEDESCRIPTION top
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)](../man3/isspace.3.html)) 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 top
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](../man3/errno.3.html)_ is set to **ERANGE**.
Precisely the same holds for **strtoll**() (with **LLONG_MIN** and
**LLONG_MAX** instead of **LONG_MIN** and **LONG_MAX**).ERRORS top
This function does not modify _[errno](../man3/errno.3.html)_ 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](../man3/errno.3.html)_ to **EINVAL** in case no
conversion was performed (no digits seen, and 0 returned).ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌───────────────────────────────┬───────────────┬────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├───────────────────────────────┼───────────────┼────────────────┤
│ **strtol**(), **strtoll**(), **strtoq**() │ Thread safety │ MT-Safe locale │
└───────────────────────────────┴───────────────┴────────────────┘VERSIONS top
According to POSIX.1, in locales other than "C" and "POSIX", these
functions 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 **strtol**().STANDARDS top
C11, POSIX.1-2008.HISTORY top
**strtol**()
POSIX.1-2001, C89, SVr4, 4.3BSD.
**strtoll**()
POSIX.1-2001, C99.CAVEATS top
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](../man3/errno.3.html)_ to 0 before the
call, and then determine 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 differentiate the errors.
errno = 0;
strtol("0", NULL, base);
if (errno == EINVAL)
goto unsupported_base;EXAMPLES top
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)](../man3/atoi.3.html), 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 rangeProgram 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 top
[atof(3)](../man3/atof.3.html), [atoi(3)](../man3/atoi.3.html), [atol(3)](../man3/atol.3.html), [strtod(3)](../man3/strtod.3.html), [strtoimax(3)](../man3/strtoimax.3.html), [strtoul(3)](../man3/strtoul.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 strtol(3)
Pages that refer to this page:pmstore(1), pmtrace(1), atof(3), atoi(3), scanf(3), sscanf(3), strtod(3), strtoimax(3), strtoul(3), slapo-retcode(5), bpf-helpers(7)