strtol(3) - NetBSD Manual Pages

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STRTOL(3)               NetBSD Library Functions Manual              STRTOL(3)


NAME

     strtol, strtoll, strtoimax, strtoq -- convert string value to a long,
     long long, intmax_t or quad_t integer


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #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);


DESCRIPTION

     The 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 deter-
     mined 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.)


RETURN VALUES

     The 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.


EXAMPLES

     Because the return value of 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 trail-
     ing whitespace is acceptable, further checks must be done on *ep; alter-
     nately, 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;


ERRORS

     [EINVAL]           The base is not between 2 and 36 and does not contain
                        the special value 0.

     [ERANGE]           The given string was out of range; the value converted
                        has been clamped.


SEE ALSO

     atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtou(3), strtoul(3),
     strtoull(3), strtoumax(3)


STANDARDS

     The 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.


BUGS

     Ignores the current locale.

NetBSD 10.1                    November 4, 2016                    NetBSD 10.1