strtol(3C) Standard C Library Functions strtol(3C)
strtol, strtoll, atol, atoll, atoi, lltostr, ulltostr - string conversion routines
long strtol(const char *restrict str, char **restrict endptr, int base);
long long strtoll(const char *restrict str, char **restrict endptr, int base);
long atol(const char *str);
long long atoll(const char *str);
int atoi(const char *str);
char *lltostr(long long value, char *endptr);
char *ulltostr(unsigned long long value, char *endptr);
strtol() and strtoll()
The strtol() function converts the initial portion of the string pointed to by str to a type long int representation.
The strtoll() function converts the initial portion of the string pointed to by str to a type long long representation.
Both functions first decompose the input string into three parts: an initial, possibly empty, sequence of white-space characters (as speci-
fied by isspace(3C)); a subject sequence interpreted as an integer represented in some radix determined by the value of base; and a final
string of one or more unrecognized characters, including the terminating null byte of the input string. They then attempt to convert the
subject sequence to an integer and return the result.
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. A decimal constant begins with a non-zero digit, and consists of a sequence of decimal dig-
its. An octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 to 7 only. A hexadecimal constant con-
sists 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 respec-
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; only letters whose ascribed values are less than that of base are permitted. 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.
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 contains no characters if the input string is empty or consists entirely of white-space
characters, or if 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 is
interpreted as an integer constant. If the subject sequence has the expected form and the value of base is between 2 and 36, it is used as
the base for conversion, ascribing to each letter its value as given above. If the subject sequence begins with a minus sign, the value
resulting from the conversion is negated. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr
is not a null pointer.
In other than the POSIX locale, additional implementation-dependent subject sequence forms may be accepted.
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of str is stored in the object
pointed to by endptr, provided that endptr is not a null pointer.
atol(), atoll() and atoi()
Except for behavior on error, atol() is equivalent to: strtol(str, (char **)NULL, 10).
Except for behavior on error, atoll() is equivalent to: strtoll(str, (char **)NULL, 10).
Except for behavior on error, atoi() is equivalent to: (int) strtol(str, (char **)NULL, 10).
If the value cannot be represented, the behavior is undefined.
lltostr() and ulltostr()
The lltostr() function returns a pointer to the string represented by the long long value. The endptr argument is assumed to point to the
byte following a storage area into which the decimal representation of value is to be placed as a string. The lltostr() function converts
value to decimal and produces the string, and returns a pointer to the beginning of the string. No leading zeros are produced, and no ter-
minating null is produced. The low-order digit of the result always occupies memory position endptr-1. The behavior of lltostr() is unde-
fined if value is negative. A single zero digit is produced if value is 0.
The ulltostr() function is similar to lltostr() except that value is an unsigned long long.
Upon successful completion, strtol(), strtoll(), atol(), atoll(), and atoi() return the converted value, if any. If no conversion could be
performed, strtol() and strtoll() return 0 and errno may be set to EINVAL.
If the correct value is outside the range of representable values, strtol() returns LONG_MAX or LONG_MIN and strtoll() returns LLONG_MAX or
LLONG_MIN (according to the sign of the value), and errno is set to ERANGE.
Upon successful completion, lltostr() and ulltostr() return a pointer to the converted string.
The strtol() and strtoll() functions will fail if:
ERANGE The value to be returned is not representable. The strtol() and strtoll() functions may fail if:
EINVAL The value of base is not supported.
Because 0, LONG_MIN, LONG_MAX, LLONG_MIN, and 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, call the function, then check errno and if it is non-zero, assume an error has
The strtol() function no longer accepts values greater than LONG_MAX or LLONG_MAX as valid input. Use strtoul(3C) instead.
Calls to atoi() and atol() might be faster than corresponding calls to strtol(), and calls to atoll() might be faster than corresponding
calls to strtoll(). However, applications should not use the atoi(), atol(), or atoll() functions unless they know the value represented by
the argument will be in range for the corresponding result type.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Interface Stability |See below. |
|MT-Level |MT-Safe |
The strtol(), strtoll(), atol(), atoll(), and atoi() functions are Standard.
isalpha(3C), isspace(3C), scanf(3C), strtod(3C), strtoul(3C), attributes(5), standards(5)
SunOS 5.10 6 May 2003 strtol(3C)