File I/O help

Quote:

---

Originally Posted by JasonBB

Wait, then how do I modify the string with my function?

---

I think the real problem is that you took code that IMO was written off the top of someone's head and untested, and now trying to get it to work.

Let's start from the beginning:

What does your input file look like? Does it contain carriage-return/line feeds? If so, how do you handle this if you encounter one before you've read in 350 characters?

If you want to handle CR/LF yourself, the file should be opened in binary mode, not text mode -- then you can use the gcount() member function to determine the actual number of characters read in.

The correct way to set up this type of a program is to break it down into functions, and not try to do everything in main(). This way, you have some sort of a plan as to how to write the program.

Code:

---

#include <fstream>
#include <vector>

const int numBytes = 350;

int ReadBytes(std::ifstream& theStream, std::vector<char>& thedata)
{
    // reads in 350 (or less bytes) and stores in data
    // returns the number of bytes read.  If 0, then no bytes
    // were read in.
    //...
    //
}

void ProcessData( std::vector<char>& theData )
{
}

int main()
{
    std::vector<char> myBuffer;

    std::ifstream instream;
    instream.open("whatever.txt");
    while (ReadBytes(instream, myBuffer) )
    {
        ProcessData( myBuffer );
        // now process the characters in myBuffer
    }
}

---

Regards,

Paul McKenzie

It appears to be the buffer. It reads in all of the character alright, but somehow some extra things are added to it.

If you do this:

Code:

---

cout << buffer[i] << endl;

---

in the for loop, it looks fine. But, if you do this after the loop for:

Code:

---

cout << &buffer[0] << endl;

---

You get the string and some extra stuff.

It looks like the stuff gets added on the second go around, as well. The first 350 chars look fine, but the second don't.

Sorry, I didn't see your last post. Yes, I agree that I need to set this up better. Give me a few minutes and I'll rework this a bit before we dive in further.

Okay, forgive me but this will be a long post. The test.txt file looks like this for now (later on the real file will not have many line breaks-- if any-- and it will be much longer).

Quote:

---

Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good.

---

When I run the code, enc.txt looks like this:

Quote:

---

Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encrysýýýý««««««««îþîþîþt works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking goodýýýý««««««««îþîþîþ. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encýýýý««««««««îþîþîþryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking gýýýý««««««««îþîþîþood.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if ýýýý««««««««îþîþîþencryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not lookinýýýý««««««««îþîþîþg good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see ýýýý««««««««îþîþîþif encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not loýýýý««««««««îþîþîþoking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to ýýýý««««««««îþîþîþsee if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's noýýýý««««««««îþîþîþt looking good.ÿorks. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good. Hello! this is a test to see if encryst works. So far, it's not looking good.
Hello! this is a test to see if encryst works. So far, it's noýýýý««««««««îþîþîþ

---

Here is an update on the code so far:

Code:

---

#include<string>

#include<iostream>

#include<fstream>

#include<stdio.h>

#include<vector>

usingnamespace std;

/* other functions here */
int processFile(char* fin, char* fout, int type = 1){

ifstream file_in;

ofstream file_out;

file_in.open(fin, ios_base::in);

file_out.open(fout, ios_base::out);

string mystring;

std::vector<char> buffer(350);

while(!file_in.eof()) {

for (int i = 0; i < 350 && !file_in.eof(); i++) {

buffer[i] = file_in.get();

}

mystring = &buffer[0];

//mystring = my_functio(mystring);

file_out << mystring;

}

file_in.close();

file_out.close();



return 1;

}

int main(int arg_num, char* args[]){



processFile("test.txt","enc.txt");

system("pause");
 
return 0;
}

---

Quote:

---

Originally Posted by JasonBB

It appears to be the buffer. It reads in all of the character alright, but somehow some extra things are added to it.

But, if you do this after the loop for:

Code:

---

cout << &buffer[0] << endl;

---

You get the string and some extra stuff.

---

Which is why I stated to drop doing this and use cout.write().

The operator << for cout when a char* is encountered expects the data to be null terminated -- your data is not null-terminated.

Regards,

Paul McKenzie

I'm sorry. You are correct. I changed that, and now it almost works. It is sooo close. It adds one extra character to the end of the file.

here is the updated function:

Code:

---

int processFile(char* fin, char* fout, int type = 1){
 
ifstream file_in;
 
ofstream file_out;
 
file_in.open(fin, ios_base::in);
 
file_out.open(fout, ios_base::out);
 
string mystring;
 
std::vector<char> buffer(350);
 
while(!file_in.eof()) {
 
unsignedint x = 0;
 
for (int i = 0; i < 350 && !file_in.eof(); i++) {
 
buffer[i] = file_in.get();
 
++x;
 
}
 
mystring = &buffer[0];
 
//mystring = my_function(mystring);
 
file_out.write(&buffer[0], x);
 
}
 
file_in.close();
 
file_out.close();
 
 
 
return 1;
 
}
 


---

Also, how do I rework this:

Code:

---

mystring = my_function(mystring);

---

?

EDIT: What is up with the editor, here? It removes random spaces, like "unsigned int" to "unsignedint" and "#include <iostream>" to "#include<iostream>". :confused:

So, I added this:

Code:

---

if(file_in.eof()){x = x-1;}

---

after the for loop, and it seems to do the trick, but I don't know if that is a good option. What do you think?
I still can't figure out how to implement my_function(), though.

I wrote a function that should do what you want. I put comments on all lines to help let you understand what is going on.

EDIT:
Fixed errors in code. Thanks to Paul McKenzie for pointing them out and telling me about using vectors with chars :D
I did add more to it aswell.

Code:

---

#include <iostream>
#include <fstream>
#include <vector>

#include <windows.h>

using namespace std;

bool GrabFileData(const string& FilePath,  vector<char>& SBuffer){ // my little function{ // my little function

                ifstream MyFile( FilePath.c_str(), ios::binary | ios::ate ); // open the file as binary and goto end
                if(MyFile.is_open() == false) return false; // looks like the file didn't exist

                SBuffer.resize( MyFile.tellg() ); // read our cursor pos which would be the total of characters since we are at the end our file and resize the vector to hold all of the file
                MyFile.seekg(0); // goto the beginning
                MyFile.read(&SBuffer[0], SBuffer.size()); // read it into the buffer
                MyFile.close(); // close the file

                return true; // success
}

bool GrabFileData(const string& FilePath,  string& SBuffer){ // my little function{ // my little function

                vector<char> Data; // to hold our data from file
                bool Success = GrabFileData(FilePath, Data); // call the vector type GrabFileData function
                SBuffer.assign(Data.begin(), Data.end()); // copy the vector info to the string

                return Success; // return if it worked or not
}

int main()
{

        string Data; // to hold our data from file
        if( GrabFileData( "c:/test.txt", Data) ){ // put context of the file to data

        for(unsigned int I = 0; I < Data.length(); I++){ // simple loop on string

                cout << Data[I];

        }

        cout << endl << endl;
        cout << "The length of the file in characters is: " << Data.length() << endl;

        }else{

                cout << "Does that file exist?" << endl;

        }

        return 0;
}

---

This code compiles without any errors or warnings for me.

1)

Code:

---

delete CBuffer; // delete what we created or it will be stuck in

---

That is the wrong form of delete. Correction:

Code:

---

delete [] CBuffer;

---

2) Pass things as strings as either references or const references, not by value:

Code:

---

bool GrabFileData(const string& FilePath, string& SBuffer){ // my little function

---

3)

Code:

---

char* CBuffer; // dim a pointer for creation of an array later

---

Usage of std::vector<char> eliminates the need for new[]/delete[].

Code:

---

std::vector<char> CBuffer;
//...
CBuffer.resize(Length);
MyFile.read(&CBuffer[0], Length); // read it into the buffer
//...
SBuffer.append(&CBuffer[0], Length ); // append the char array to

---

Quote:

---

Although I do recommend you making sure the new operator can create enough room in the memory for the file.

---

Operator new[] throws an exception (std::bad_alloc) if there is no memory. So it is impossible to not check, since the check is done automatically.

Regards,

Paul McKenzie

Thanks for the the code, Joeman. I will be taking a closer look at that later to hopefully help me learn more about file I/O. But for now, the code I have is working, I just need to know how to change this:

Code:

---

mystring = my_function(mystring);

---

so that it works with the code I have. Buffer is the var being read in and written to a file, but I need to pass a string into the function, and the function returns a string. Once I solve that, it should be done :)

Quote:

---

Originally Posted by JasonBB

I just need to know how to change this:

Code:

---

mystring = my_function(mystring);

---

---

Show us the function.

Regards,

Paul McKenzie

Thanks Paul McKenzie for clearing some problems up with my code. I edited my post with your corrections and made more adjustments to it. Can you make sure I didn't do anything wrong to it?

Code:

---


#include<string>
 
#include<iostream>
 
#include<fstream>
 
#include<stdio.h>
 
#include<vector>
 
usingnamespace std;
 
/* functions */
 
int processFile(char* fin, char* fout, int type = 1){
ifstream file_in;
 
ofstream file_out;
 
file_in.open(fin, ios_base::in);
 
file_out.open(fout, ios_base::out);
 
string mystring;
 
std::vector<char> buffer(350);
 
while(!file_in.eof()) {
 
unsigned int x = 0;
 
for (int i = 0; i < 350 && !file_in.eof(); i++) {
 
buffer[i] = file_in.get();
 
++x;
 
}
 
mystring = &buffer[0];
 
if(type == 1){
 
mystring = my_function(mystring);
 
}else{
 
mystring = my_function(mystring);
 
}
 
if(file_in.eof()){x = x-1;}
 
file_out.write(&buffer[0], x);
 
}
 
file_in.close();
 
file_out.close();
 
 
 
return 1;
 
}
 
int main(int arg_num, char* args[]){
processFile("test.txt","enc.txt");
system("pause");

return 0;
}


---

You didn't post the my_function() function.

Regards,

Paul McKenzie

I can't for security reasons (the software is for website security). Basically, though, it's:

Code:

---

string my_function(string mystring){
 
//changes
//send to another function
//changes
//send to yet another function
 
return mystring;
}

---

That's really all I can show you. Basically, I just need to put the string back into the buffer, if that's possible.