strtoul(3) - OpenBSD manual pages

NAME

strtoul, strtoull, strtoumax, strtouq — convert a string to an unsigned long, unsigned long long or uintmax_t integer

SYNOPSIS

#include <limits.h>
#include <stdlib.h>

unsigned long
strtoul(const char *nptr, char **endptr, int base);

unsigned long long
strtoull(const char *nptr, char **endptr, int base);

#include <inttypes.h>

uintmax_t
strtoumax(const char *nptr, char **endptr, int base);

#include <sys/types.h>
#include <limits.h>
#include <stdlib.h>

u_quad_t
strtouq(const char *nptr, char **endptr, int base);

The strtoul() function converts the string in nptr to an unsigned long value. The strtoull() function converts the string in nptr to an unsigned long long value. The strtoumax() function converts the string in nptr to a umaxint_t value. The strtouq() function is a deprecated equivalent of strtoull() and is provided for backwards compatibility with legacy programs. The conversion is done according to the given base, which must be a number between 2 and 36 inclusive or the special value 0. If the string in nptr represents a negative number, it will be converted to its unsigned equivalent. This behavior is consistent with what happens when a signed integer type is cast to its unsigned counterpart.

The string may begin with an arbitrary amount of whitespace (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 an unsigned long, unsigned long long, or uintmax_t 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-null, strtoul() stores the address of the first invalid character in *endptr. If there were no digits at all, however, strtoul() 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 strtoul(), strtoull(), strtoumax() and strtouq() functions return either the result of the conversion or, if there was a leading minus sign, the negation of the result of the conversion, unless the original (non-negated) value would overflow. If overflow occurs, strtoul() returns ULONG_MAX, strtoull() returns ULLONG_MAX, strtoumax() returns UINTMAX_MAX, strtouq() returns ULLONG_MAX and the global variable errno is set to ERANGE.

There is no way to determine if strtoul() has processed a negative number (and returned an unsigned value) short of examining the string in nptr directly.

If there is no valid digit, 0 is returned. If base is invalid, 0 is returned and the global variable errno is set to EINVAL.

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 strtoul(), and the return value of strtoul() cannot be used unambiguously to signal an error:

char *ep;
unsigned long ulval;

...

errno = 0;
ulval = strtoul(buf, &ep, 10);
if (buf[0] == '\0' || *ep != '\0')
	goto not_a_number;
if (errno == ERANGE && ulval == ULONG_MAX)
	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).

ERRORS

[EINVAL]: The value of base was neither between 2 and 36 inclusive nor the special value 0.
[ERANGE]: The given string was out of range; the value converted has been clamped.

STANDARDS

The strtoul(), strtoull(), and strtoumax() functions conform to ISO/IEC 9899:1999 (“ISO C99”). Setting errno to EINVAL is an extension to that standard required by IEEE Std 1003.1-2008 (“POSIX.1”).

The strtouq() function is a BSD extension and is provided for backwards compatibility with legacy programs.

BUGS

Ignores the current locale.

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