strtol() -- General Function (libc)

Convert string to long integer
#include <stdlib.h>
long strtol(string, tailptr, base)
char *string; char **tailptr; int base;

strtol() converts  the number  given in  string to a  long and  returns its
value; it is  a more general version of the  function atol(). strtol() also
stores  a  pointer to  the  first character  following  the number  through
tailptr, provided tailptr does not equal NULL.

base gives the  base of the number being read,  either zero or a value from
two to 36.  If the given base is zero, strtol() determines an implicit base
for the number:  hexadecimal if the number starts with   0x or 0X, octal if
the number  starts with  0, or  decimal otherwise.  Alternatively,  you can
specify a base between 2 and 36.

strtol() parses  string into  three portions: beginning,  subject sequence,
and tail.

The beginning  consists of zero  or more white-space  characters that begin
the string.

The subject  sequence is the  portion of the string  that strtol() converts
into a long. It consists of  an optional sign character, an optional prefix
0x  or 0X  if the  base is  16, and  a nonempty sequence  of digits  in the
specified base.   For example, if the base is  16, then strtol() recognizes
numeric characters `0' to `9' and alphabetic characters `A' through `F' and
`a' to `f' as digits.  It continues to scan until it encounters a nondigit.

The  tail continues  from  the end  of  the subject  sequence  to the  null
character that ends the string.

strtol()  ignores the  beginning portion  of the  string.  It  converts the
subject sequence  to a long. Finally,  if tailptr is not  NULL, it sets the
pointer pointed to by tailptr to  the address of the first character of the
string's tail.

strtol() returns a long representing the value of the subject sequence.  If
the  input string  does not  specify a  valid number,  it returns  zero and
stores the initial value of string through tailptr. If the number it builds
is too large  or too small to fit into  a long, it sets the global variable
errno to  the value of the  macro ERANGE and returns  LONG_MAX or LONG_MIN,
respectively.

See Also

libc
ANSI Standard, §7.10.1.5

Notes

strtol() ignores  initial white space  in the input string.  White space is
defined as being all characters so recognized by the function isspace().

© 2012 by Stephen A. Ness