Read line after line but from the eof.

[Ground21]

Hello.
How could I read the whole text file line after line from the end of
file? (I want to ~copy~ file)

I want to copy file in this way:

file 1:

a
b
c
file 2:

c
b
a
--
Ground21_______ _____\\
ground21@poczta KROPKAfm

[Rolf Magnus]

Ground21 wrote:

Hello.
How could I read the whole text file line after line from the end of
file? (I want to ~copy~ file)

I want to copy file in this way:

file 1:

a
b
c
file 2:

c
b
a

The easiest way would be to read all the lines into something like an
std::vector<std ::string, then write the new file iterating backwards
through the vector. As long as you don't have huge files, this should work
ok.

[Ground21]

The easiest way would be to read all the lines into something like an
std::vector<std ::string, then write the new file iterating backwards
through the vector. As long as you don't have huge files, this should work
ok.

I think I wrote bad example:

Once more:

file1:

text1
text2
text3
abctest

file2:

abctest
text3
text2
text1
--
Ground21_______ _____\\
ground21@poczta KROPKAfm

[Rolf Magnus]

Ground21 wrote:

>

>The easiest way would be to read all the lines into something like an
std::vector<st d::string, then write the new file iterating backwards
through the vector. As long as you don't have huge files, this should
work ok.

I think I wrote bad example:

I did understand your posting anyway.

Once more:

file1:

text1
text2
text3
abctest

file2:

abctest
text3
text2
text1

Yup. What you should do is read the file line by line and put each line as a
separate string into a vector. So later you have a vector of lines. Then
you can iterate through that vector backwards and write the strings out
again.

[Ondra Holub]

Rolf Magnus napsal:

Ground21 wrote:

The easiest way would be to read all the lines into something like an
std::vector<std ::string, then write the new file iterating backwards
through the vector. As long as you don't have huge files, this should
work ok.

I think I wrote bad example:

I did understand your posting anyway.

Once more:

file1:

text1
text2
text3
abctest

file2:

abctest
text3
text2
text1

Yup. What you should do is read the file line by line and put each line as a
separate string into a vector. So later you have a vector of lines. Then
you can iterate through that vector backwards and write the strings out
again.

I would recommend std::list instead of std::vector, because list can be
simplier (== more effectively) extended in length.

[red floyd]

Ondra Holub wrote:

Rolf Magnus napsal:

>Ground21 wrote:

>>>The easiest way would be to read all the lines into something like an
std::vector< std::string, then write the new file iterating backwards
through the vector. As long as you don't have huge files, this should
work ok.
I think I wrote bad example:

I did understand your posting anyway.

>>Once more:

file1:

text1
text2
text3
abctest

file2:

abctest
text3
text2
text1

Yup. What you should do is read the file line by line and put each line as a
separate string into a vector. So later you have a vector of lines. Then
you can iterate through that vector backwards and write the strings out
again.

I would recommend std::list instead of std::vector, because list can be
simplier (== more effectively) extended in length.

I used deque.

I tried to be real clever, with reverse_copy on an istream_iterato r, and
an ostream_iterato r, but reverse_copy requires Bidirectional Iterators. :(

[Ground21]

Rolf Magnus napisał(a):

Yup. What you should do is read the file line by line and put each line as a
separate string into a vector. So later you have a vector of lines. Then
you can iterate through that vector backwards and write the strings out
again.

can You tell me what's wrong with this code?:
(I want to save lines from file 'file' to vectors, and then, write them
into "tmp.txt"). I got wrong output "tmp.log".. . I think that is problem
with char*...

#include <vector.h>
vector <char*tab(10) ;

tmp=fopen("tmp. txt","w");
fseek(file, 0L, SEEK_SET);
for(int i=0; i<lines; i++)
{
fgets(tab[i],256,file);
}
for(int i=lines; i>0; i--)
{
fputs(tab[i],tmp);
}
--
Ground21_______ _____\\
ground21@poczta KROPKAfm

[red floyd]

Ground21 wrote:

Rolf Magnus napisał(a):

>Yup. What you should do is read the file line by line and put each
line as a
separate string into a vector. So later you have a vector of lines. Then
you can iterate through that vector backwards and write the strings out
again.

can You tell me what's wrong with this code?:
(I want to save lines from file 'file' to vectors, and then, write them
into "tmp.txt"). I got wrong output "tmp.log".. . I think that is problem
with char*...

#include <vector.h>
vector <char*tab(10) ;

tmp=fopen("tmp. txt","w");
fseek(file, 0L, SEEK_SET);
for(int i=0; i<lines; i++)
{
fgets(tab[i],256,file);
}
for(int i=lines; i>0; i--)
{
fputs(tab[i],tmp);
}

Lets see...

1. What is "lines"?
2. What happens if there are more than 10 lines in a file?
3. What happens if a line is bigger than 256?
4. Why are you using arrays and C-style I/O?
5. What is <vector.h>? The C++ header is <vector>
6. Every entry in your vector is identical, since you're storing the
same address over and over.

And that's just off the top of my head.

[Ground21]

red floyd napisał(a):

1. What is "lines"?

int lines=0;
fseek(fileh,0L, SEEK_SET);
while(feof(file h)==0) if(fgetc(fileh) =='\n') linies++;

lines - number of lines in my text file.

2. What happens if there are more than 10 lines in a file?

I read in wikibooks, that value of size will automaticlly increase if
necessary...

3. What happens if a line is bigger than 256?

I know, that it can be done better using something like strlen to check
line lenght, but for me, 256 is OK.

4. Why are you using arrays and C-style I/O?
5. What is <vector.h>? The C++ header is <vector>

in c++ builder 6 it works the same for <vectorand <vector.h>...

6. Every entry in your vector is identical, since you're storing the
same address over and over.

I though, that I take first line to tab[0], second line to tab[1]...

--
Ground21_______ _____\\
ground21@poczta KROPKAfm

[r]

Ground21 wrote:

>
can You tell me what's wrong with this code?:
(I want to save lines from file 'file' to vectors, and then, write them
into "tmp.txt"). I got wrong output "tmp.log".. . I think that is problem
with char*...

#include <vector.h>
vector <char*tab(10) ;

tmp=fopen("tmp. txt","w");
fseek(file, 0L, SEEK_SET);
for(int i=0; i<lines; i++)
{
fgets(tab[i],256,file);
}
for(int i=lines; i>0; i--)
{
fputs(tab[i],tmp);
}

It's a bad mix of C and C++, besides the "Access violation".

// reading a file line by line
std::ifstream ifs ("tmp.txt");
std::string line;
std::vector<std ::stringlines;
while (getline (ifs, line)) {
lines.push_back (line);
}

Is this already in the C++ FAQ?