strtol(3) - OpenBSD manual pages

NAME

strtol, strtoll, strtoimax, strtoq — convert string value to a long, long long or intmax_t integer

SYNOPSIS

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

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

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

#include <inttypes.h>

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

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

quad_t
strtoq(const char *nptr, char **endptr, int base);

The strtol() function converts the string in nptr to a long value. The strtoll() function converts the string in nptr to a long long value. The strtoimax() function converts the string in nptr to an intmax_t value. The strtoq() function is a deprecated equivalent of strtoll() 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.

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 a long, long long, or intmax_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, 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(), strtoll(), strtoimax(), and strtoq() functions return the result of the conversion. If overflow or underflow occurs, errno is set to ERANGE and the function return value is as follows:

Function	underflow	overflow
`strtol`()	`LONG_MIN`	`LONG_MAX`
`strtoll`()	`LLONG_MIN`	`LLONG_MAX`
`strtoimax`()	`INTMAX_MIN`	`INTMAX_MAX`
`strtoq`()	`LLONG_MIN`	`LLONG_MAX`

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

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

[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 strtol(), strtoll(), and strtoimax() 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 strtoq() function is a BSD extension and is provided for backwards compatibility with legacy programs.

BUGS

Ignores the current locale.

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