strtol, strtoll, atol, atoll, atoi, lltostr, ulltostr - string conver‐
long strtol(const char *restrict str, char **restrict endptr, int base);
long long strtoll(const char *restrict str, char **restrict endptr,
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);
DESCRIPTIONstrtol() 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 rep‐
resented in some radix determined by the value of base; and a final
string of one or more unrecognized characters, including the terminat‐
ing 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 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 sub‐
ject sequence is a sequence of letters and digits representing an inte‐
ger 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 charac‐
ters 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 inter‐
preted 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
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) str‐
tol(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 termi‐
nating null is produced. The low-order digit of the result always occu‐
pies memory position endptr−1. The behavior of lltostr() is undefined
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 EIN‐
If the correct value is outside the range of representable values, str‐
tol() 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
Upon successful completion, lltostr() and ulltostr() return a pointer
to the converted string.
The strtol() and strtoll() functions will fail if:
The value to be returned is not representable. The strtol()
and strtoll() functions may fail if:
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 occurred.
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
SEE ALSOisalpha(3C), isspace(3C), scanf(3C), strtod(3C), strtoul(3C),
May 6, 2003 STRTOL(3C)