Help with fstream in cpp | Together C & C++ | Page 1

wet drum Feb 23, 2023, 7:00 PM

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Hi, I'm actually creating a project and so for that I decided to create my version of file management with a class but my problem is that I added a function called "changeMode" and that's to change the open mode of the file, here the code

void personal::File::changeMode(std::ios_base::_Openmode mode)
{
    m_out->close();
    delete(m_out);
    m_out = new std::ofstream(m_outPath, mode);
}

and I get an error when I want to use the function with the parameter, I'll write down the error just bellow but the code where the error is, is here

if (m_mode == std::ios_base::app)
{
    changeMode(std::ios_base::out);
}
*m_out << finalText;

short stormBOT Feb 23, 2023, 7:00 PM

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wet drum Feb 23, 2023, 7:01 PM

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if types are not correct it's normal I try many of them like the default std::ios::out but it don't work

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so the error is :

C++ the object has type qualifiers that are not compatible with the member function        
    
object type is: const personal::File

halcyon oriole Feb 23, 2023, 7:03 PM

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changeMode modifies the File, but said File is const. Can't change a constant.

wet drum Feb 23, 2023, 7:03 PM

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um

rich geode Feb 23, 2023, 7:03 PM

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why do you create them with new?

wet drum Feb 23, 2023, 7:03 PM

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rich geode why do you create them with new?

it's pointers and I need to have pointers to expand lifetime

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it's created on heap

rich geode Feb 23, 2023, 7:04 PM

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and how long is the lifetime supposed to be?

wet drum Feb 23, 2023, 7:04 PM

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halcyon oriole `changeMode` modifies the `File`, but said `File` is `const`. Can't change a con...

um you wan tthe definition in header ?

wet drum Feb 23, 2023, 7:04 PM

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rich geode and how long is the lifetime supposed to be?

out of the function, but idk why I try to deal without new at the start but it didn't work

halcyon oriole Feb 23, 2023, 7:05 PM

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wet drum um you wan tthe definition in header ?

No. When you said "the error is, is here" you seem to be in a const member function. Make it not const.

rich geode Feb 23, 2023, 7:05 PM

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wet drum out of the function, but idk why I try to deal without new at the start but it d...

the lifetime of your fields are the lifetime of your object, not the function

wet drum Feb 23, 2023, 7:05 PM

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I send all my code with header and definitions so you all can see

rich geode Feb 23, 2023, 7:05 PM

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you have zero reasons to use heap allocations here

wet drum Feb 23, 2023, 7:05 PM

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halcyon oriole No. When you said "the error is, is here" you seem to be in a `const` member fun...

Just wait I send that

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it didn't work without

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so idk

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so first module.h :

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#pragma once

#include <string>
#include <fstream>

namespace personal
{
    //create string class


    class File
    {
    public: // enums
        enum WriteMode : char
        {
            INSERT = 0,
            REPLACE
        };

    public : // methods
        /* 
        * Constructor of File
        * @param path : the path of the file you write and read in
        * @param mode : the mode of opening the file (default = std::ios::out)
        */
        File(std::string& const path, std::ios::_Openmode mode = std::ios_base::out);
        File(File& const file);

        ~File();

        /*
        Get the file's path you read in
        */
        std::string path() const { return m_path;};
        /*
        Get the file's path you write in
        */
        std::string outPath() const { return m_outPath; };

        /*
        Set the file's path you read in
        */
        void path(std::string& path);
        /*
        Set the file's path you write in
        */
        void outPath(std::string& path);

        /*
        Change the mode of the file stream you write in
        */
        void changeMode(std::ios_base::_Openmode mode);

        /*
        * Write in the file
        * @param text : you seriously ask what is this param ???
        * @param pos : the position where you write your text
        * @param mode : the writing mode ( default = WriteMode.INSERT, can be REPLACE)
        */
        void write(std::string& text, int pos = 0, WriteMode mode = INSERT) const;

    private :  // attributes
        std::ofstream* m_out;
        std::ios_base::openmode m_mode;
        std::string m_outPath;

        std::string m_path;
        std::ifstream* m_file;

        std::string m_text;
    };
}

halcyon oriole Feb 23, 2023, 7:06 PM

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You can also just use open to change the mode.

wet drum Feb 23, 2023, 7:06 PM

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halcyon oriole You can also just use `open` to change the mode.

how ?

halcyon oriole Feb 23, 2023, 7:06 PM

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https://en.cppreference.com/w/cpp/io/basic_ofstream/open

wet drum Feb 23, 2023, 7:07 PM

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File.cpp :

#include "module.h"

personal::File::File(std::string& const path, std::ios::_Openmode mode) :
    m_path(path), m_mode(mode), m_outPath(path), m_text("")
{
    m_file = new std::ifstream(path);
    m_out = new std::ofstream(path, mode);
    
}

personal::File::File(File& const file)
{
    m_path = file.m_path;
    m_out = new std::ofstream(file.m_outPath, file.m_mode);
    m_file = new std::ifstream(file.m_path);
}

personal::File::~File()
{
    delete(m_out);
    delete(m_file);
}



void personal::File::path(std::string& path)
{
    m_path = path;

    m_file->close();
    delete(m_file);
    m_file = new std::ifstream(path);
}

void personal::File::outPath(std::string& path)
{
    m_path = path;

    m_out->close();
    delete(m_out);
    m_out = new std::ofstream(path, m_mode);
}

void personal::File::changeMode(std::ios_base::_Openmode mode)
{
    m_out->close();
    delete(m_out);
    m_out = new std::ofstream(m_outPath, mode);
}

void personal::File::write(std::string& text, int pos, WriteMode mode) const
{
    std::string finalText = m_text;
    if (mode == File::INSERT)
    {
        m_out->seekp(pos);
        *m_out << text;
    }
    else if (mode == File::REPLACE)
    {
        for (int i = pos; i < text.length(); i++)
        {
            // if we replace a char
            if (finalText.length()+1 > pos+i)
            {
                finalText[i] = text[i];
            }
            //if we need to add a text at the end
            else
            {
                finalText[i] += text[i];
            }
        }

        if (m_mode == std::ios_base::app)
        {
            changeMode(std::ios_base::out);
        }
        *m_out << finalText;
    }

    // change m_text
}

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I look up I say to you

halcyon oriole Feb 23, 2023, 7:08 PM

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void personal::File::write(std::string& text, int pos, WriteMode mode) const
That const at the end says you will not change File, so you can't call changeMode.

wet drum Feb 23, 2023, 7:08 PM

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halcyon oriole > void personal::File::write(std::string& text, int pos, WriteMode mode) const T...

oh thank, but it shouldn't be there

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I remove that thx

wet drum Feb 23, 2023, 7:09 PM

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halcyon oriole You can also just use `open` to change the mode.

you think that open is more convenient here ?

halcyon oriole Feb 23, 2023, 7:10 PM

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Yes. Better than that constant new and delete.

wet drum Feb 23, 2023, 7:10 PM

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and yes it's solved by removing that const

halcyon oriole Feb 23, 2023, 7:10 PM

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I'm not sure if you need to close before calling open again. Probably.

wet drum Feb 23, 2023, 7:11 PM

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halcyon oriole Yes. Better than that constant `new` and `delete`.

idk why but I try to deal with normal stack allocation in the constructor but in the func write it does an error when I wanted to get the cursor

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and with new it work well

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!solved

#Help with fstream in cpp