STRTOL(3P)

💖 STRTOL(3P) 💖

okay bestie, sit down, hydrate, because today we're talking about strtol and strtoll — the POSIX Programmer's Manual girlies. this page lives in the POSIX Programmer's Manual, and quick heads up before we go any further: the Linux implementation of this interface may differ (so go check the matching Linux manual page for the deets on Linux behavior), or the interface might not even be implemented on Linux at all. 🙈 not me warning you first thing, but that's the vibe.

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✨ NAME ✨

strtol, strtoll — convert a string to a long integer. that's it, that's the job, and they ate. 💅

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🦋 SYNOPSIS 🦋

#include <stdlib.h>

long strtol(const char *restrict nptr, char **restrict endptr, int base);
long long strtoll(const char *restrict nptr, char **restrict endptr,
    int base)

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🌸 DESCRIPTION 🌸

first things first, the functionality described on this reference page is aligned with the ISO C standard. any conflict between the requirements described here and the ISO C standard is unintentional, and this volume of POSIX.1‐2017 defers to the ISO C standard. we respect the canon, no cap. 👑

so these functions shall convert the initial portion of the string pointed to by nptr into a type long and long long representation, respectively. and how do they do it? they decompose the input string into three parts, like a little three-act play:

1. an initial, possibly empty, sequence of white-space characters (as specified by isspace())
2. a subject sequence interpreted as an integer represented in some radix determined by the value of base
3. a final string of one or more unrecognized characters, including the terminating NUL character of the input string

then they shall attempt to convert the subject sequence to an integer, and return the result. iconic behavior tbh.

if the value of base is 0, the expected form of the subject sequence is that of a decimal constant, octal constant, or hexadecimal constant — any of which may be preceded by a '+' or '-' sign. let's break that down:

• a decimal constant begins with a non-zero digit, and consists of a sequence of decimal digits.
• an octal constant consists of the prefix '0' optionally followed by a sequence of the digits '0' to '7' only.
• a hexadecimal constant consists of the prefix 0x or 0X followed by a sequence of the decimal digits and letters 'a' (or 'A') to 'f' (or 'F') with values 10 to 15 respectively.

if the value of base is between 2 and 36, the expected form of the subject sequence is a sequence of letters and digits representing an integer with the radix specified by base, optionally preceded by a '+' or '-' sign. the letters from 'a' (or 'A') to 'z' (or 'Z') inclusive are ascribed the values 10 to 35, and only letters whose ascribed values are less than that of base are permitted. and if the value of base is 16, the characters 0x or 0X may optionally precede the sequence of letters and digits, following the sign if present. 💜

okay now the definition, because this part matters: the subject sequence is defined as the longest initial subsequence of the input string, starting with the first non-white-space character, that is of the expected form. the subject sequence shall contain no characters if:

• the input string is empty, or
• it consists entirely of white-space characters, or
• the first non-white-space character is other than a sign or a permissible letter or digit

if the subject sequence has the expected form and the value of base is 0, the sequence of characters starting with the first digit shall be interpreted as an integer constant. if the subject sequence has the expected form and the value of base is between 2 and 36, it shall be used as the base for conversion, ascribing to each letter its value as given above. and if the subject sequence begins with a <hyphen-minus>, the value resulting from the conversion shall be negated. 🫶

a pointer to the final string shall be stored in the object pointed to by endptr, provided that endptr is not a null pointer.

in other than the C or POSIX locale, additional locale-specific subject sequence forms may be accepted. (yes, locales really said "let me add some lore." 🌈)

if the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr shall be stored in the object pointed to by endptr, provided that endptr is not a null pointer.

these functions shall not change the setting of errno if successful. periodt.

⚠️ listen up because this is the trap: since 0, {LONG_MIN} or {LLONG_MIN}, and {LONG_MAX} or {LLONG_MAX} are returned on error and are also valid returns on success, an application wishing to check for error situations should set errno to 0, then call strtol() or strtoll(), then check errno. do all three steps, bestie, don't skip the vibe check. 🔥

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💫 RETURN VALUE 💫

upon successful completion, these functions shall return the converted value, if any. if no conversion could be performed, 0 shall be returned and errno may be set to [EINVAL].

if the value of base is not supported, 0 shall be returned and errno shall be set to [EINVAL].

if the correct value is outside the range of representable values, {LONG_MIN}, {LONG_MAX}, {LLONG_MIN}, or {LLONG_MAX} shall be returned (according to the sign of the value), and errno set to [ERANGE]. she overflowed, your honor. 😭

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🎀 ERRORS 🎀

these functions shall fail if:

• EINVAL — the value of base is not supported.
• ERANGE — the value to be returned is not representable.

these functions may fail if:

• EINVAL — no conversion could be performed.

the following sections are informative. (translation: the main character part is over, this is bonus content. 💖)

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⭐ EXAMPLES ⭐

None.

(it's giving "no thoughts, head empty." nothing to show here, moving on. 🦋)

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🍓 APPLICATION USAGE 🍓

since the value of *endptr is unspecified if the value of base is not supported, applications should either:

• ensure that base has a supported value (0 or between 2 and 36) before the call, or
• check for an [EINVAL] error before examining *endptr

pick one, don't be out here reading *endptr off vibes alone. 🙈

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🧚 RATIONALE 🧚

None.

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🌈 FUTURE DIRECTIONS 🌈

None.

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👑 SEE ALSO 👑

• fscanf()
• isalpha()
• strtod()

and from the Base Definitions volume of POSIX.1‐2017: <stdlib.h>

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💜 COPYRIGHT 💜

portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group.

in the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. the original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. to report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay and that's the whole page bestie, we made it to the end 🎉

this one's brought to you by IEEE/The Open Group, dated 2017, and it's the STRTOL(3P) page — take care of her, she's iconic. mwah. 💅✨💖