another c++ i/o questions

[Doug Harvey]

I have a question that hopefully someone here has already figured out.

I have more experience programming in "C", and in order to improve I/O
throughput we would use setvbuf() to increase the buffer size that
fread/read used when reading files. It made a pretty big difference.
I tried the following:

char mybuffer[1000000];
inp.rdbuf()->pubsetbuf(mybuffer,1000000);

while (getline((inp),line)) {
...

but it changed the output, seemed like it no longer read all of the
data.
Any thoughts on the above would be appreciated.

Also, is the read() function the proper way to read fixed-length records
using the C++ i/o libraries?
Thanks in advance of course.

doug

--

[Victor Bazarov]

Doug Harvey wrote:

I have a question that hopefully someone here has already figured out.

I have more experience programming in "C", and in order to improve I/O
throughput we would use setvbuf() to increase the buffer size that
fread/read used when reading files. It made a pretty big difference.
I tried the following:

char mybuffer[1000000];
inp.rdbuf()->pubsetbuf(mybuffer,1000000);

while (getline((inp),line)) {
...

but it changed the output,
In what way? What was the output before and what is it after? "Changed"
isn't much to work on.
seemed like it no longer read all of the
data.
How much of the data does it read? 10%? 90%? 99.9%? What's missing?
Any thoughts on the above would be appreciated.
From the archives: pubsetbuf does not guaranteed to turn buffering on.
See this: http://tinyurl.com/7a9a6 (I searched for 'pubsetbuf')

Also, is the read() function the proper way to read fixed-length records
using the C++ i/o libraries?

Sure.

Perhaps you could be a good sport and read the FAQ first. Perhaps after
that you would consider following the recommendation of FAQ 5.8...

V