--- name: "strtol" section: "3" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/strtol" --- # strtol(3) string to long int ## NAME strtol, strtoll, strtoq - string to long int ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include ``` **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)](/feature_test_macros/7.md)): **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 determined by [**isspace**(3)](/isspace/3.md)) 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' 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 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)](/attributes/7.md). | | | | | --- | --- | --- | | **Interface** | **Attribute** | **Value** | | **strtol**(), **strtoll**(), **strtoq**() | Thread safety | MT-Safe locale | ## VERSIONS 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 C23, POSIX.1-2024. ## HISTORY - **strtol**() POSIX.1-2001, C89, SVr4, 4.3BSD. - **strtoll**() POSIX.1-2001, C99. - "0b", "0B" C23. glibc 2.38. (Not in POSIX.) ## CAVEATS ### 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 == _Minof(long)) || n < min) goto too_low; if ((errno == ERANGE && n == _Maxof(long)) || 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 ### White space These functions silently accept leading white space. To reject white space, call [**isspace**(3)](/isspace/3.md) before **strtol**(). ## 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)](/atoi/3.md), 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 #include #include 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)](/atof/3.md), [**atoi**(3)](/atoi/3.md), [**atol**(3)](/atol/3.md), [**strtod**(3)](/strtod/3.md), [**strtoimax**(3)](/strtoimax/3.md), [**strtoul**(3)](/strtoul/3.md)