Specifying number of lines to be read

[corp1117]

Hi,

I wrote a script to remove a chunk of data ( a matrix) from one file and operate on it. I then wanted to put it back into the original file and replace the old matrix. I was told I could not put data lines back into the old file (the matric is in the middle of other data). So I tried to put it into a new file, and altered my program to also copy the previous data and put it all in the right order. My original file contains 9000 lines of 5 large floatiing point numbers. Is there a way to tell it to copy all these lines in a shorthand way, I can't imagine I need to write out:

fscanf(in, "%f etc...) and

then use printf 9000 times. Can anybody help me with this?

Thanks, Michael

[Banfa]

If you know the position in the original file of the start and end of the data you are reading and writing then you can use

fread and fwrite (you will be reading and writing in binary mode).

In theory you could write the new file in 3 logical steps

1. Write the beginning of the file
   Call fread to read the entire beginning of the original file in 1 chunk
   Call fwrite to write the beginning of the new file in 1 chunk
2. Write your new data
3. Write the end of the file
   Call fread to read the entire end of the original file in 1 chunk
   Call fwrite to write the end of the new file in 1 chunk

You may find that there is a limitation in that you have to supply the buffer for fread and fwrite to read and write into/out of so for a really large file in reality you may have to perform the block read/writes in a number of steps (say use a buffer of 10240 bytes and read and write blocks in multiples of that size) so you may want to create a wrapper function that takes the offset in the original file and the size of the data to copy and then internally if required does the copy in several steps.

When working out offsets and sizes fseek and ftell should come in handy.