July 23, 2009 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

```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`)

```intmax_t` strtoimax(```const char * restrict nptr``, char ** restrict endptr``, int base`)

```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 determined 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' representing 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`.

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 (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 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 (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.