dear there,
I need to read a large file line by line into a vector, and it is inefficient to let vector resize itself as needed. so i would like to count how many lines are there, reserve the vector size, and read from the beginning of the file line by line again.
can anyone give me an idea how to count, and how to move point to beginning of the file again? Thanks.
The rewind() function resets the file position to the start.
Although, with a smart standard library I'll contend that reading the file twice is not necessarily faster than letting the vector resize, especially if you give it a good initial size. For example, Microsoft's STL in VS 2008 is smart, and will not create copies of all the strings during a resize. So is GCC's STL in 4.3 and higher, if you enable C++0x features (rvalue references).
All the buzzt!
CornedBee
"There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
- Flon's Law
If the file is very large, it is extremely likely that it will take longer to read it twice.
Also, if you do your own resizing (e.g. reserve double the size when you run out of current size), you can reduce the number of times the vector is resized.
--
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
Vector usually doubles its size anyway.
All the buzzt!
"There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
- Flon's Law
>> it is inefficient to let vector resize itself as needed
As indicated by the other posters, this may not be true. Did you profile it or are you just making that assumption?
