Manpages - strtol.3
Table of Contents
NAME
strtol, strtoll, strtoq - convert a string to a long integer
SYNOPSIS
#include <stdlib.h> long strtol(const char *restrict nptr, char **restrict endptr, int base); long long strtoll(const char *restrict nptr, char **restrict endptr, int base);
Feature Test Macro Requirements for glibc (see *feature_test_macros*(7)):
*strtoll*():
_ISOC99_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
DESCRIPTION
The *strtol*() function converts the initial part of the string in nptr to a long integer value 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” or “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 uppercase or lowercase represents 10, ’B’ represents 11, and so forth, with ’Z’ representing 35.)
If endptr is not NULL, *strtol*() stores the address of the first invalid character in *endptr. If there were no digits at all, *strtol*() stores the original value of nptr in *endptr (and returns 0). In particular, if *nptr is not ’\0’ but **endptr is ’\0’ on return, the entire string is valid.
The *strtoll*() function works just like the *strtol*() function but returns a long long integer value.
RETURN VALUE
The strtol*() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, *strtol*() returns *LONG_MIN. If an overflow occurs, strtol*() returns *LONG_MAX. In both cases, errno is set to ERANGE. Precisely the same holds for strtoll*() (with *LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).
ERRORS
- EINVAL
- (not in C99) The given base contains an unsupported value.
- ERANGE
- The resulting value was out of range.
The implementation may also set errno to EINVAL in case no conversion was performed (no digits seen, and 0 returned).
ATTRIBUTES
For an explanation of the terms used in this section, see *attributes*(7).
| Interface | Attribute | Value |
| *strtol*(), *strtoll*(), *strtoq*() | Thread safety | MT-Safe locale |
CONFORMING TO
*strtol*(): POSIX.1-2001, POSIX.1-2008, C89, C99 SVr4, 4.3BSD.
*strtoll*(): POSIX.1-2001, POSIX.1-2008, C99.
NOTES
Since strtol*() can legitimately return 0, *LONG_MAX, or LONG_MIN (LLONG_MAX or LLONG_MIN for *strtoll*()) on both success and failure, the calling program should set errno to 0 before the call, and then determine if an error occurred by checking whether errno has a nonzero value after the call.
According to POSIX.1, in locales other than “C” and “POSIX”, these functions may accept other, implementation-defined numeric strings.
BSD also has
quad_t strtoq(const char *nptr, char **endptr, int base);
with completely analogous definition. Depending on the wordsize of the current architecture, this may be equivalent to *strtoll*() or to *strtol*().
EXAMPLES
The program shown below demonstrates the use of *strtol*(). The first command-line argument specifies a string from which *strtol*() should parse a number. The second (optional) argument specifies the base to be used for the conversion. (This argument is converted to numeric form using *atoi*(3), a function that performs no error checking and has a simpler interface than *strtol*().) Some examples of the results produced by this program are the following:
$ ./a.out 123 strtol() returned 123 $ ./a.out ' 123' strtol() returned 123 $ ./a.out 123abc strtol() returned 123 Further characters after number: "abc" $ ./a.out 123abc 55 strtol: Invalid argument $ ./a.out '' No digits were found $ ./a.out 4000000000 strtol: Numerical result out of range
Program source
#include <stdlib.h>
#include <limits.h>
#include <stdio.h>
#include <errno.h>
int
main(int argc, char *argv[])
{
int base;
char *endptr, *str;
long val;
if (argc < 2) {
fprintf(stderr, "Usage: %s str [base]\n", argv[0]);
exit(EXIT_FAILURE);
}
str = argv[1];
base = (argc > 2) ? atoi(argv[2]) : 0;
errno = 0; /* To distinguish success/failure after call */
val = strtol(str, &endptr, base);
/* Check for various possible errors. */
if (errno != 0) {
perror("strtol");
exit(EXIT_FAILURE);
}
if (endptr == str) {
fprintf(stderr, "No digits were found\n");
exit(EXIT_FAILURE);
}
/* If we got here, strtol() successfully parsed a number. */
printf("strtol() returned %ld\n", val);
if (*endptr != '\0') /* Not necessarily an error... */
printf("Further characters after number: \"%s\"\n", endptr);
exit(EXIT_SUCCESS);
}
SEE ALSO
*atof*(3), *atoi*(3), *atol*(3), *strtod*(3), *strtoimax*(3), *strtoul*(3),
COLOPHON
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