File reading and writing!

**Adamkromm** · 10-14-2005

is there a way to read in a file one char at a time then when a certain letter is met you can overwrite what comes next or insert text after it??

as far as i know the only way to write to a file is either to truncate it or append neither is what i want

really my problem lies in writing to the file because i can do everything up till that point

thx

**SlyMaelstrom** · 10-14-2005

Yes.

What you want to do is create a filestream to open your file. Then write a loop that reads in a single character from the stream, then checks to see if it's the character you want. If it isn't, it will concatinate it onto a string variable then read in another character. If it is the character you want, it will exit the loop, then you just concatinate what you want to add onto your string. Then you write that to a new file.

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main() {
    
    char readIn;
    string acceptedTxt;
    
    ifstream inFile ("hello.txt");
    
    while (acceptedTxt != "Hello,") {
       readIn = inFile.get();
       
       acceptedTxt = acceptedTxt + readIn;
       }
       
    acceptedTxt = acceptedTxt + " Fred!";

    
    inFile.close();
    
    ofstream outFile ("hello.txt");
    
    outFile << acceptedTxt;
    
    return 0;
}

What this program will do, if put into the same folder as my attached text, will change the text in the file "Hello, Sarah!" into "Hello, Fred!".

It reads in up to the part you want, then changes the rest.

I hope that's what you were looking for.

**Ancient Dragon** · 10-14-2005

if you are attempting to insert characters into the file, you will need to use two files -- input file and temporary output file. Read the characters from the input file then write what you want to the output file. After the input file is completly read, close both files, delete the input file and finally rename the temporary output file to the same name as the original input file.

**Daved** · 10-14-2005

If the text you want to replace is the same size as the text you want to replace it with, you can do it with only one file by using fstream and seekg or seekp or something like that. I don't remember the details, but if you search for fstream and seek you might find it.

**Adamkromm** · 10-14-2005

basicaly what im trying to do is if i have this in a file

Code:

Hold me now, oh hold me now
Till this hour has gone around
And I gone, on the rising tide
For to face Van Diemen's land.

the user inputs a word to replace lets say hold
then a word to replace it with(same length) lets say AAAA

then the program finds and replaces all occurances of hold giving

Code:

Hold me now, oh AAAA me now
Till this hour has gone around
And I gone, on the rising tide
For to face Van Diemen's land.

i think i might be able to figure it out with what has been said thx alot

**Adamkromm** · 10-17-2005

can fstream file("*.*") be used for text or just binary...

if it can be used for text i cant figure out how.

**Daved** · 10-17-2005

Assuming you put a filename in there instead of wildcards, yes. In fact, it is used for text by default. If you want binary you have to specify binary. Show your code and describe the issues you are having.

**Adamkromm** · 10-17-2005

first i tried this

Code:

int main()
{
    fstream file("hello.txt");
    file<<"hello"<<endl;
    file.close();
}

and it didnt even make a file.

then i tried

Code:

fstream file;
file.open("hello.txt");

and that did nothing

so then i tried

Code:

int main()
{
    fstream file;
    file.open("hello.txt");
    file.write("hey", 3);
    file.close();
}

and it still didnt even make a file

then i tried

Code:

int main()
{
    fstream file;
    file.open("hello.txt", ios::out);
    file<<"hey"<<endl;
    file.close();
}

and it worked !! but when i changed it to
file.open("hello.txt", ios:

ut | ios::in );
it doesnt work...

so i guess my new question is how do i make a fstream that reads and writes

**Daved** · 10-17-2005

If the file does not exist it will fail to open for reading. So check for fail() and if it is true then just use ios_base::out to open the file. This is a quick example that does work:

Code:

#include <fstream>
using namespace std;

int main()
{
    fstream file("Fout.txt", ios_base::out | ios_base::in);
    if (file.fail())
    {
        file.clear();
        file.open("Fout.txt", ios_base::out);
    }

    if (file.good())
        file << "hey" << endl;

    file.close();
}

**Adamkromm** · 10-18-2005

thanks that helps alot... and seekg seekp pointers remain independant right?

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