reading strings from a binary .txt file

This is a discussion on reading strings from a binary .txt file within the C++ Programming forums, part of the General Programming Boards category; My program saves customer data to a .txt file in binary. Fields such as name and address are typed in ...

  1. #1
    Master of Puppets rwmarsh's Avatar
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    reading strings from a binary .txt file

    My program saves customer data to a .txt file in binary. Fields such as name and address are typed in as a C++ string, converted to a C style char array, and saved to disk (since the compiler will not let me save a c++string, only a char array). These same fields can also be loaded into a C style char array and converted back to a string (for the ease of manipulation). I am using stringstreams to do the conversions but I am getting no results.

    Code:
    //  save customer profile to disk
    
    int saveprof()
    {
        ofstream fcust(c:\\cust_data.txt",ios::binary | ios::app);
        if (fcust.fail()) 
        { cout<<"\nCannot open library file!\a"; }
        else
        {
            string temp;
            temp.assign(custinfo.cust_name, 0, 26);
            fcust.write(temp.c_str(),26);
            temp.assign(custinfo.cust_address, 0, 26);
            fcust.write(temp.c_str(),26);
            temp.assign(custinfo.cust_city, 0, 16);
            fcust.write(temp.c_str(),16);
            temp.assign(custinfo.cust_state, 0, 3);
            fcust.write(temp.c_str(),3);
            fcust.write(reinterpret_cast<char*>(&custinfo.cust_zip), sizeof(int));
            temp.assign(custinfo.cust_contact, 0, 26);
            fcust.write(temp.c_str(),26);
            temp.assign(custinfo.cust_phone, 0, 13);
            fcust.write(temp.c_str(),13);
            cout<<"\nFile saved";
            fcust.close();
        }
        return 0;
    }
    
    
    //  load customer profile from disk
    
    int findprof()
    {
        ifstream fcust("c:\\cust_data.txt", ios::binary);
        if (fcust.fail())
        { cout<<"\nCannot open library file!\a"; }
        else
        {
            istringstream sstream(ctemp);
            getline(sstream, custinfo.cust_name);
            sstream.str("");
            fcust.read(ctemp,26);
            sstream.str(ctemp);
            getline(sstream, custinfo.cust_address);
            sstream.str("");
            fcust.read(ctemp,16);
            sstream.str(ctemp);
            getline(sstream, custinfo.cust_city);
            sstream.str("");
            fcust.read(ctemp,3);
            sstream.str(ctemp);
            getline(sstream, custinfo.cust_state);
            sstream.str("");        
            fcust.read(reinterpret_cast<char*>(&custinfo.cust_zip), sizeof(int));
            fcust.close();
        }
        return 0;
    }
    The customer name comes up just fine but all the other string fields come up blank. (the zip code works fine, also)

    Using DEV-C++ Under Windows XP

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    Try the FAQ under such subjects as "getting a line from the user (C++)".
    dwk

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  3. #3
    Registered User Tonto's Avatar
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    If your 'customer' or whatever class is just 'plain old data', or something like this:

    Code:
    struct customer
    {
    	char cust_name[26];
    	char cust_address[26];
    	char cust_state[3];
    	char cust_contact[26];
    	char cust_phone[13];
    	int cust_zip;
    }
    Then you can just:

    Code:
    	// write
    
    	std::ofstream o("test.txt", std::ios::binary);
    
    	customer c(...);
    
    	o.write(reinterpret_cast<char*>(&c), sizeof(c));
    
    	// read
    
    	std::ifstream i("test.txt", std::ios::binary);
    
    	customer c;
    
    	i.read(reinterpret_cast<char*>(&c), sizeof(c));

  4. #4
    Confused Magos's Avatar
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    Why are you using "binary" files when handling text? Wouldn't it be way easier using text methods from the beginning?

    Code:
    struct CInfo
    {
      std::string Name;
      std::string Address;
      std::string Phone;
    };
    
    void Save(const CInfo& Info)
    {
      std::ofstream File("SomeFile.txt");
    
      File << Info.Name << std::endl;
      File << Info.Address << std::endl;
      File << Info.Phone << std::endl;
    }
    
    void Load(CInfo& Info)
    {
      std::ifstream File("SomeFile.txt");
    
      std::getline(File, Info.Name);
      std::getline(File, Info.Address);
      std::getline(File, Info.Phone);
    }
    (this, of course, assumes that each string field occupies no more than 1 line)
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  5. #5
    Cat without Hat CornedBee's Avatar
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    And why are you giving binary files a .txt extension?
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  6. #6
    Master of Puppets rwmarsh's Avatar
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    Why are you using "binary" files when handling text? Wouldn't it be way easier using text methods from the beginning?
    Yes, it would be easier to use text methods, but then I would not learn how to work with binary methods.

    The point is I have heard that you can use stringstreams to convert from a char array to a string, but everything I have tried just produces an empty string. Is it possible to do this or is there an easier way? I have searched and googled until I was blue in the face and could not come up with anything.....
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  7. #7
    Confused Magos's Avatar
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    No need for stringstreams, std::string has a constructor that takes a char pointer:
    Code:
    char CharArray[32];
    std::string String = CharArray;
    Make sure the array ends with a NULL terminator ( '\0' ).
    If this is not the case, you could use a temporary buffer:
    Code:
    char CharArrayWithNoNullTerminator[32];
    std::vector<char> TempBuffer;
    TempBuffer.resize(32 + 1);
    std::memcpy(&TempBuffer[0], CharArrayWithNoNullTerminator, 32);
    TempBuffer[32] = '\0';
    std::string String = &TempBuffer[0];
    MagosX.com

    Give a man a fish and you feed him for a day.
    Teach a man to fish and you feed him for a lifetime.

  8. #8
    Master of Puppets rwmarsh's Avatar
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    Now, I could swear I did that before and it did not work.... Now it does....

    Maybe I just THOUGHT I did that... Oh well, Thanks for the help! I knew there was an easier way... Maybe I just need to get some sleep..........
    Using DEV-C++ Under Windows XP
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    "No! Do, or Do Not. There is no Try..."

  9. #9
    Registered User
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    Quote Originally Posted by Magos

    std::string has a constructor that takes a char pointer...Make sure the array ends with a NULL terminator ( '\0' ). If this is not the case, you could use a temporary buffer
    Code:
    char CharArrayWithNoNullTerminator[32];
    std::vector<char> TempBuffer;
    TempBuffer.resize(32 + 1);
    std::memcpy(&TempBuffer[0], CharArrayWithNoNullTerminator, 32);
    TempBuffer[32] = '\0';
    std::string String = &TempBuffer[0];
    No need for all that. There is a string constructor that can handle non null terminated char arrays, as well:
    Code:
    const int size = 3;
    char NoNullTerminator[size] = {'y', 'e', 's'};
    	
    string myString(NoNullTerminator, size);
    cout<<myString.c_str()<<endl;
    ...and you can do more straight forward things like this as well:
    Code:
    string myString1;
    myString.assign(NoNullTerminator, size);
    cout<<myString.c_str()<<endl;
    
    string myString2;
    myString2.append(NoNullTerminator, size);
    cout<<myString2.c_str()<<endl;
    
    string myString3;
    myString3.insert(myString3.end(), NoNullTerminator, NoNullTerminator + size);
    cout<<myString2.c_str()<<endl;
    Last edited by 7stud; 03-05-2006 at 08:32 PM.

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