Re: how to match a particular string in a input file

James Kanze <>
Mon, 13 Apr 2009 02:54:11 -0700 (PDT)
On Apr 12, 5:04 am, Pradeep <> wrote:

I have a file a log.txt. I have read the file each line with
the following.

         ifstream inputFile("log.txt");
          std::string line;
          if (inputFile.is_open())
                  while (! inputFile.eof() )

This will probably cause you to skip the last line.

Where do people "learn" this sort of thing? (It's a frequent
error, so somewhere, it must be being taught.) The standard
idiom for reading lines from a stream is either:

    std::string line ;
    while ( std::getline( inputFile, line ) ) ...

or to define a class Line, with an overloaded operator<<, use:

    Line line ;
    while ( inputFile >> line ) ...

(For most types, the class is the way to go, but in the case of
lines, it's less certain---usually, a "line" doesn't correspond
to anything in the application; it's just a convenient way to
parse the file, with resynchronization in case of error.)

                          getline (inputFile,line,"\n");
                        // cout << line << endl;

log.txt is of following form
Source File: m.log
File Size: 45333 bytes
Start Time: Feb 20 2000
Dest. File: dest.log

m.log is already in prescribed file format.

Which is? <label>:<data>, with the first colon
as separator? Or something else? (Does what follows the colon
have some specific format, for example.)

My Question is If I want to read a partial message "already in
a prescribed format" in a line how do I do that?

What do you mean by a "partial message"?

Splitting strings at the first colon is trivial:

    std::string line ;
    // ...
            = std::find( line.begin(), line.end(), ':' ) ;
    if ( pivot == line.end() ) {
        // error, no colon found...
    } else {
        std::string label( line.begin(), pivot ) ;
        std::string data( pivot + 1, line.end() ) ;
        // ...

James Kanze (GABI Software)
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