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' 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 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 upper or lower
     case represents 10, `B' represents 11, and so forth, with `Z' represent-
     ing 35.)

     If endptr is non nil, strtol() stores the address of the first invalid
     character in *endptr.  If there were no digits at all, however, strtol()
     stores 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.


EXAMPLES

     Ensuring that a string is a valid number (i.e., in range and containing
     no trailing characters) requires clearing errno beforehand explicitly
     since errno is not changed on a successful call to strtol(), and the
     return value of strtol() cannot be used unambiguously to signal an error:

           char *ep;
           long lval;

           ...

           errno = 0;
           lval = strtol(buf, &ep, 10);
           if (buf[0] == '\0' || *ep != '\0')
                   goto not_a_number;
           if (errno == ERANGE && (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 (buf[0] == '\0' || *ep != '\0')
                   goto not_a_number;
           if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN)) ||
               (lval > INT_MAX || lval < INT_MIN))
                   goto out_of_range;
           ival = lval;


ERRORS

     [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), 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'').


BUGS

     Ignores the current locale.

NetBSD 4.0                      August 11, 2002                     NetBSD 4.0