STRTOL(3) | NetBSD Library Functions Manual | STRTOL(3) |
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);
#include <inttypes.h>
intmax_t
strtoimax(const char * restrict nptr, char ** restrict endptr, int base);
#include <sys/types.h>
#include <stdlib.h>
#include <limits.h>
quad_t
strtoq(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 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.)
If no error occurs, errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards.
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;
July 23, 2009 | NetBSD 5.99 |