On 26.06.2024 22:44, Thiago Adams wrote:

How to copy a file on linux keeping the original file information?
timestamp etc?

This is an OS question and I'm not sure you want the shell command
or the library function.

On a Linux shell I do

cp -p # to preserve attributes
cp -a # incl. -p, to do a lot like copying recursive a directory

Or in other words the equivalent of CopyFileA from windows.

And what exactly does it do? (Windows has - for example, since you
mentioned time stamps above - other time information than Unix
systems. So it may not be what you expect.)

Janis

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(Followup set to comp.unix.programmer)

On Wed, 26 Jun 2024 15:35:00 -0700, Keith Thompson wrote:

Thiago Adams <[email protected]> writes:

How to copy a file on linux keeping the original file information?
timestamp etc?

Or in other words the equivalent of CopyFileA from windows.

comp.unix.programmer is likely to give you better answers. I don't
think POSIX defines any functions that copy files.

No, AFAIK, POSIX doesn't define an "all-in-one" file copy function.
However, Linux (the OS Thiago asks about) defines a number of them.

If I uunderstand correctly, you want to do the equivalent of "cp -p",

Which /can/ be accomplished with POSIX calls
- the standard I/O functions (fopen()/open(), fread()/read(),
fwrite()/write(), fclose()/close() ) to copy the file data
- stat() to obtain the "original file information", and
- utime() to set the copy timestamps,
- chmod() to set the copy file permissions
- chown() to set the file ownership

But, perhaps Thiago would be satisfied with just a hardlinked file.

but from C rather than from a shell. You might consider using system(),
but that has some drawbacks, and there are probably better ways.

HTH
--
Lew Pitcher
"In Skills We Trust"

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On Wed, 26 Jun 2024 17:44:48 -0300, Thiago Adams wrote:

How to copy a file on linux keeping the original file information?
timestamp etc?

Last-modified is usually the only timestamp people care about.

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Lawrence D'Oliveiro <[email protected]d> writes:

On Wed, 26 Jun 2024 17:44:48 -0300, Thiago Adams wrote:

How to copy a file on linux keeping the original file information?
timestamp etc?

Last-modified is usually the only timestamp people care about.

Do you think before you post?

That's not true.

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Bonita Montero <[email protected]> writes:

I tried to implement that in C++. Unfortunately an error branch of the
code is taken. What Do I have to change ?

You need to figure out which error branch is taken and
look at errno and the surrounding logic at that point
to see why the call failed.

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Oops. missed part of my edit. See unquoted line below

On Fri, 28 Jun 2024 23:25:20 +0000, Lew Pitcher wrote:

On Sat, 29 Jun 2024 00:04:00 +0100, Malcolm McLean wrote:

On 28/06/2024 19:15, Bonita Montero wrote:

int fromFile = open( from, O_RDONLY | O_NOATIME );
    if( !fromFile )
        return false;

open() returns -1 on failure, and some non-negative number
on success. That non-negative number /can be/ 0 and still
be a valid success value.

The above test /will not/ detect an open() failure, as !(-1) == 0
However, the above /will/ falsely call

a FAILURE (and return a "false" from the function)

a valid open() that returns
fd 0 (slim chance unless you've previously closed stdin).

   invoke_on_destruct closeFrom( [&] { close( fromFile ); } );
//    int toFile = open( to, O_CREAT );
//    if( !toFile )
//        return false;
    invoke_on_destruct closeTo( [&] { close( toFile ); } );
//     invoke_on_destruct delTo( [&] { unlink( to ); } );
    for( int64_t remaining = attrFrom.st_size; remaining > 0; remaining
-= 0x100000 )
    {
        size_t n = (size_t)(remaining >= 0x100000 ? 0x100000 : remaining);
        buf.resize( n );
        if( read( fromFile, buf.data(), n ) )
        {
            // this branch is taken
            cout << strerror( errno ) << endl;
            return false;
        }

So it claims the file opens, then won't read it?

Check the call. Is 0 the success return?

Then I must admit I'm stumped. "to" doesn't alias "from" I suppose?

I'd also wonder if somehow the C++ compiler has invoked the on destruct
code, and closed the file.

--
Lew Pitcher
"In Skills We Trust"

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On Sat, 29 Jun 2024 00:04:00 +0100, Malcolm McLean wrote:

On 28/06/2024 19:15, Bonita Montero wrote:

int fromFile = open( from, O_RDONLY | O_NOATIME );
    if( !fromFile )
        return false;

open() returns -1 on failure, and some non-negative number
on success. That non-negative number /can be/ 0 and still
be a valid success value.

The above test /will not/ detect an open() failure, as !(-1) == 0
However, the above /will/ falsely call a valid open() that returns
fd 0 (slim chance unless you've previously closed stdin).

   invoke_on_destruct closeFrom( [&] { close( fromFile ); } );
//    int toFile = open( to, O_CREAT );
//    if( !toFile )
//        return false;
    invoke_on_destruct closeTo( [&] { close( toFile ); } );
//     invoke_on_destruct delTo( [&] { unlink( to ); } );
    for( int64_t remaining = attrFrom.st_size; remaining > 0; remaining >> -= 0x100000 )
    {
        size_t n = (size_t)(remaining >= 0x100000 ? 0x100000 : remaining);
        buf.resize( n );
        if( read( fromFile, buf.data(), n ) )
        {
            // this branch is taken
            cout << strerror( errno ) << endl;
            return false;
        }

So it claims the file opens, then won't read it?

Check the call. Is 0 the success return?

Then I must admit I'm stumped. "to" doesn't alias "from" I suppose?

I'd also wonder if somehow the C++ compiler has invoked the on destruct
code, and closed the file.

--
Lew Pitcher
"In Skills We Trust"

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