SAS/C Library Reference, Vol. 1

atol -- Convert a String to Long

SYNOPSIS

 #include <stdlib.h>

 long int atol(const char *str);

DESCRIPTION

atol converts the character string str to a long integer. The string should consist of an optional plus or minus sign, followed by one or more decimal digits. Initial white-space characters are ignored.

RETURN VALUE

atol returns the integer value represented by the character string, up to the first unrecognized character. If no initial segment of the string is a valid integer, the return value is 0L.

CAUTION

No indication of overflow or other error is returned, so you should validate the string before calling atol.

DIAGNOSTICS

No indication is returned to the program to specify whether the string contains a valid integer.

If the correct value is too large to be stored in a 370 long, either LONG_MAX (2**31 - 1) or LONG_MIN ( - 2**31) is returned, depending on the sign of the value.

EXAMPLE

  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>

  #define MAXLINE 25

  main()
  {
    long value;
    char *input;
    char line[MAXLINE];

    puts("Enter a number: ");
    input = gets(line);

       /* If string contains only digits, white space, or +/-,  */
       /*  convert. Note that the input may still not represent */
       /*  a valid integer. Consider +-14+5.                    */
    if (strspn(input, " +-0123456789") == strlen(input)){
       value = atol(input);
       printf("The long integer equivalent of given string is %ldn",
       value);
    }
    else
      printf("Invalid count value: %sn", input);
  }

RELATED FUNCTIONS

strtol