On 06/04/2012 10:28 AM, Corey Bryant wrote:
But at least strtol lets you detect errors:
char *tmp;
errno = 0;
fd = strtol(p,&tmp, 10);
if (errno || tmp == p) {
/* raise your error here */
}
I don't think this is legitimate. errno can be set under the covers of
library calls even if the strtol() call is successful.
Wrong. POSIX _specifically_ requires that strtol() leave errno
unchanged unless strtol() is reporting a failure, no matter what other
library calls (if any) are made under the covers by strtol().
In other words, pre-setting errno to 0, then calling strtol(), then
checking errno, _is_ the documented way to check for strtol() failures,
and a correct usage of strtol() MUST use this method. See also commit
6b0e33be88bbccc3bcb987026089aa09f9622de9. atoi() does not have this
same guarantee, which makes atoi() worthless at detecting errors in
relation to strtol().
I was thinking if strtol returns 0 and errno is 0, perhaps we could
assume success, but I don't think this is guaranteed either.
Actually, it _is_ guaranteed - if you pre-set errno to 0, then call
strtol(), then errno is still 0, then the result did not encounter an
error, so a result of 0 at that point means that you indeed parsed a 0.
Maybe a combination of isdigit() then strtol() will give a better idea
of success.
Not necessary.