| STRTOL(3) | Library Functions Manual | STRTOL(3) | 
strtol, strtoll,
  strtoimax, strtoq —
#include <stdlib.h>
#include <limits.h>
long int
  
  strtol(const
    char * restrict nptr,
    char ** restrict endptr,
    int base);
long long int
  
  strtoll(const
    char * restrict nptr,
    char ** restrict endptr,
    int base);
  
  #include <inttypes.h>
intmax_t
  
  strtoimax(const
    char * restrict nptr,
    char ** restrict endptr,
    int base);
  
  #include <sys/types.h>
  
  #include <stdlib.h>
  
  #include <limits.h>
quad_t
  
  strtoq(const
    char * restrict nptr,
    char ** restrict endptr,
    int base);
strtol() function converts the string in
  nptr to a long int value. The
  strtoll() function converts the string in
  nptr to a long long int value. The
  strtoimax() function converts the string in
  nptr to an intmax_t value. The
  strtoq() function converts the string in
  nptr to a quad_t value.
The conversion is done 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; 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 an appropriate 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 upper or lower case
    represents 10, ‘B’ represents 11, and
    so forth, with ‘Z’ representing
  35.)
If endptr is non-nil, the functions store
    the address of the first invalid character in *endptr.
    If there were no digits at all, however, the functions store the original
    value of nptr in *endptr. (Thus,
    if *nptr is not
    ‘\0’ but
    **endptr is ‘\0’
    on return, the entire string was valid.)
strtol() function returns the result of the
  conversion, unless the value would underflow or overflow. If an underflow
  occurs, strtol() returns
  LONG_MIN, strtoll() returns
  LLONG_MIN, and strtoimax()
  returns INTMAX_MIN. If an overflow occurs,
  strtol() returns LONG_MAX,
  strtoll() returns LLONG_MAX,
  and strtoimax() returns
  INTMAX_MAX. In these cases,
  errno is set to ERANGE. If the
  base argument is not supported then
  errno is set to EINVAL and the
  functions return 0.
If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.
strtol() cannot be used
  unambiguously to detect an error, errno is left
  unchanged after a successful call. To ensure that a string is a valid number
  (i.e., in range and containing no trailing characters), clear
  errno beforehand explicitly, then check it afterwards:
char *ep;
long lval;
...
errno = 0;
lval = strtol(buf, &ep, 10);
if (ep == buf)
	goto not_a_number;
if (*ep != '\0')
	goto trailing_garbage;
if (errno) {
	assert(errno == ERANGE);
	assert(lval == LONG_MAX || lval == LONG_MIN);
	goto out_of_range;
}
This example will accept “12” but not “12foo” or “12\n”. If trailing whitespace is acceptable, further checks must be done on *ep; alternately, use sscanf(3).
If strtol() is being used instead of
    atoi(3), error checking is
    further complicated because the desired return value is an
    int rather than a long;
    however, on some architectures integers and long integers are the same size.
    Thus the following is necessary:
char *ep; int ival; long lval; ... errno = 0; lval = strtol(buf, &ep, 10); if (ep == buf) goto not_a_number; if (*ep != '\0') goto trailing_garbage; if (errno == ERANGE || lval < INT_MIN || INT_MAX < lval) goto out_of_range; assert(errno == 0); assert(INT_MIN <= lval); assert(lval <= INT_MAX); ival = lval;
strtol() function conforms to ANSI
  X3.159-1989 (“ANSI C89”). The
  strtoll() and strtoimax()
  functions conform to ISO/IEC 9899:1999
  (“ISO C99”).
The strtoq() function is a
    BSD legacy function equivalent to
    strtoll() and should not be used in a new code.
| November 4, 2016 | NetBSD 10.0 |