Re: C++ string::find functions and size_t

[Andreas Weber]

Am 27.02.2015 um 18:47 schrieb rik:
> 2/27/15
> 
> Dan Sebald found a subtle bug in the use of the C++ string find functions
> that was leading to segfaults.
> 
> -- Code --
> size_t pos = file.find_first_not_of ("|");
> if (pos > 0)
>   file = file.substr (pos);
> else
> -- End Code --

I think the idea here was to check if the first char in file is "|" and
omit the check (because we are building a pipe) for an existent
directory in the else path.

> The issue is that the size_t is an unsigned quantity and the find functions
> do not return -1 on failure as do regular C functions.  Instead they return
> std::string::npos (a very large number) when they fail to find the search 
> term.
> 
> This was easily corrected to
> 
> -- Code --
> size_t pos = file.find_first_not_of ("|");
> if (pos != std::string::npos)
>   file = file.substr (pos);
> else
> -- End Code --

Please correct me if I'm wrong but shouldn't this then be

-- Code --
size_t pos = file.find_first_not_of ("|");
if (pos != std::string::npos && pos > 0)
-- End Code --

-- Andy