[TUHS] History of strncpy

Random832 random832 at fastmail.us
Fri Feb 1 09:52:22 AEST 2013

On 1/24/2013 9:52 AM, Warner Losh wrote:
> On Jan 24, 2013, at 7:42 AM, Ronald Natalie wrote:
>> Amen. For practical matters, there is no way given the rest of the 
>> library that an implementation can do anything other than multiply 
>> the two middle args together. 

Is there any part of the rest of the library that will be broken if it 
does something like call (e.g. on UNIX) fflush (or _flsbuf), fileno, and 
write in a loop?

vfprintf doesn't call fwrite, so it won't break sprintf.

In theory all I can even think of is if some piece of userspace code 
made assumptions about the state of a setvbuf buffer.

> Historically the only implementation I know that didn't just multiply the two args together was on VAX/VMS's VAXC. The underlying filesystem had a notion of a file of records, so you'd get very different result from n * size, 1 and n, size.

You might get a different result in terms of the resulting underlying 
file, and maybe in terms of performance, but given the requirements the 
standard puts on fread (which I don't imagine it would do if a 
then-prominent implementation violated them), I have to wonder what 
would happen, if this is the case, if you attempted to call fread when 
the file pointer is positioned on a different sized record, or in the 
middle of a record.

Because for all the concessions to non-unix-like file systems the 
standard _does_ make (binary files may be padded with extra zero bytes 
[because they may not be able to be an arbitrary size], text files may 
have a maximum line length and may not be able to contain some control 
characters, heck, _everything_ the standard says about text files is 
non-unix-like), it's IIRC rather strict about "fread has equivalent 
results to getc in a loop".

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