STRTOUL(3) | Library Functions Manual | STRTOUL(3) |
unsigned long int
strtoul(const char * restrict nptr, char ** restrict endptr, int base);
unsigned long long int
strtoull(const char * restrict nptr, char ** restrict endptr, int base);
#include <inttypes.h>
uintmax_t
strtoumax(const char * restrict nptr, char ** restrict endptr, int base);
#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>
u_quad_t
strtouq(const char * restrict nptr, char ** restrict endptr, int base);
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 an unsigned long value in the obvious manner, stopping at the end of the string or at the first character that does not produce 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, 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.)
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 the base argument is not supported then errno is set to EINVAL and the functions return 0.
If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.
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).
December 2, 2009 | NetBSD 6.1 |