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strtol(3) — Linux manual page

strtol(3) Library Functions Manual strtol(3)

NAME top

 strtol, strtoll, strtoq - convert a string to a long integer

LIBRARY 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_SOURCE

DESCRIPTION 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)) 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; if base is
 zero or 2, the string may then include a "0b" or "0B" prefix, and
 the number will be read in base 2; 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円'
 but **endptr is '0円' 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  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  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 top

 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 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

 C23, POSIX.1-2024.

HISTORY top

 strtol()
 POSIX.1-2001, C89, SVr4, 4.3BSD.
 strtoll()
 POSIX.1-2001, C99.
 "0b", "0B"
 C23. glibc 2.38. (Not in POSIX.)

CAVEATS top

 Range checks
 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 == ERANGE after the call.
 errno = 0;
 n = strtol(s, &end, base);
 if (end == s)
 goto no_number;
 if ((errno == ERANGE && n == LONG_MIN) || n < min)
 goto too_low;
 if ((errno == ERANGE && n == LONG_MAX) || n > max)
 goto too_high;
 base
 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;

BUGS top

 White space
 These functions silently accept leading white space. To reject
 white space, call isspace(3) before strtol().

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), 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
 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円') /* Not necessarily an error... */
 printf("Further characters after number: \"%s\"\n", endptr);
 exit(EXIT_SUCCESS);
 }

SEE ALSO top

 atof(3), atoi(3), atol(3), strtod(3), strtoimax(3), strtoul(3)

COLOPHON top

 This page is part of the man-pages (Linux kernel and C library
 user-space interface documentation) project. Information about
 the project can be found at 
 ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
 for this manual page, see
 ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
 This page was obtained from the tarball man-pages-6.15.tar.gz
 fetched from
 ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
 2025年08月11日. If you discover any rendering problems in this HTML
 version of the page, or you believe there is a better or more up-
 to-date source for the page, or you have corrections or
 improvements to the information in this COLOPHON (which is not
 part of the original manual page), send a mail to
 man-pages@man7.org
Linux man-pages 6.15 2025年05月17日 strtol(3)

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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)

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