如何解析一个txt文件，该文件会删除除我需要的所有行之外的所有行？

Question

I want to parse a text file to get what I want and create another txt file in c++. I have a text file which looks something like this.

User :

Group : 

Comment1 :

Comment2 :

*** Label ***

ID : Nick

PASS : sky123

Number ID : 9402

*** End of Label ***

######################################

And goes on. I basically want to create a new txt file which leaves all lines which contains colon(:) and erase the rest such as " * Label * ", and save the result in a new txt file. The answer to that txt file would be

User :

Group :

Comment1 :

Comment2 :

ID : Nick

PASS : sky123

Number ID : 9402

How do I do this in a simple way? Thank you very much.

Answer 1

In C++ with fstreams :

ifstream input("input.txt");
ofstream output("output.txt");

string line;

while (getline(input, line)) {
    if (line.find(":") != string::npos) {
        output << line << "\n";
    }
}

Answer 2

I have not tested this, but you get the idea.

void foo(ifstream& ifs, ofstream& ofs)
{
    while ( !ifs.eof() )
    {
        string line;
        getline(ifs, line);
        if (line.find(":") != string::npos)
            ofs << line;
    }
}

Answer 3

The simplist approach I can think of would be to read in the text file line by line storing only the lines you want. Once the read is complete, open a separate file for writing and write the stored lines. It's not C++ but I've written out some psuedo code to illustrate.

while(line in source file)
{
    if(wantline)
       store the line
}
for(stored lines)
   write line to destination file

Answer 4

In a big way, all you have to do is in a loop, check for each line if it have the char (:), if it does have it, add it to a string. In the end just save that string into a new text file.

Here's a tutorial of how to manage files

Answer 5

Well I don't write C++ and I'm not sure if you're looking for help with the language, but here's a simple approach in the abstract:

Load the text file into a string and then split the string into an array on the newline character so that you have 1 line of the text file per array value. Then, iterate over each element of the array. Using this method you can examine the contents of an individual line and use string comparison, regex matching, etc. to determine whether you want to keep/modify that line. Once you're done you can simply save the new string to a text file.

Alternately, you can use global find/replace with string comparison, regex etc. to apply changes to the entire document at once, but that requires more advanced knowledge and application of regex, and may not be practical given the size of the document.