reading and writing unsigned chars from a file

This is a discussion on reading and writing unsigned chars from a file within the C++ Programming forums, part of the General Programming Boards category; I'm writing an unsigned char with a value of three to a file and when I read it it's returned ...

  1. #1
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    reading and writing unsigned chars from a file

    I'm writing an unsigned char with a value of three to a file and when I read it it's returned as 255.

    Code:
    ofstream fout;
    
    fout.open("cdb.dat", ios::out | ios::binary);
    	
    unsigned char c = 3;
    fout << c;
    
    fout.close();
    
    fin.open("cdb.dat", ios::in | ios::binary);
    
    unsigned char 
    c = fin.get(),
    cout << static_cast<int>(c) << endl;
    
    fin.close();
    Can anyone please tell me what I've done wrong? Thank you for your time.

  2. #2
    Registered User Tonto's Avatar
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    Please show the exact code you use. It almost appears as if you are reading the EOF (-1) and printing that.

  3. #3
    Devil's Advocate SlyMaelstrom's Avatar
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    Yes, because minus the syntax errors, that code works perfectly on my set-up.
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  4. #4
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    Code:
    void write_breeds() // writes the file i'm reading
    {
    	ofstream fout;
    
    	fout.open("cdb.dat", ios::out | ios::binary);
    	
    	unsigned char c = 3;
    	fout << c;
    
    	// warrior
    	c = 0;
    	c |= 8 << 4 | 15;
    	fout << c;
    	
    	c = 0;
    	c |= 4 << 4 | 2;
    	fout << c;
    	
    	c = 0;
    	c |= 3 << 4 | 1;
    	fout << c;
    	
    	c = 0;
    	c |= 1 << 4 | 0;
    	fout << c;
    
    	unsigned int p = 0;
    	p |= (PROF_CS | PROF_CTS | PROF_CA | PROF_CTA | PROF_CM | PROF_CTM | PROF_CP | PROF_CST | PROF_CD | PROF_CSH | PROF_CC | PROF_CH | PROF_CL | PROF_HS | PROF_HM | PROF_HSH | PROF_HC | PROF_HH);
    	bin_write_4bytes(&fout, p);
    	
    	// priest
    	c = 0;
    	c |= 4 << 4 | 6;
    	fout << c;
    	
    	c = 0;
    	c |= 1 << 4 | 1;
    	fout << c;
    	
    	c = 0;
    	c |= 2 << 4 | 3;
    	fout << c;
    	
    	c = 0;
    	c |= 3 << 4 | 1;
    	fout << c;
    
    	p = 0;
    	p |= (PROF_CM | PROF_CST | PROF_CW | PROF_CC | PROF_HM | PROF_HC);
    	bin_write_4bytes(&fout, p);
    	
    	// mage
    	c = 0;
    	c |= 3 << 4 | 8;
    	fout << c;
    	
    	c = 0;
    	c |= 1 << 4 | 1;
    	fout << c;
    	
    	c = 0;
    	c |= 2 << 4 | 4;
    	fout << c;
    	
    	c = 0;
    	c |= 3 << 4 | 2;
    	fout << c;
    	
    	p = 0;
    	p |= (PROF_CS | PROF_CM | PROF_CST | PROF_CW | PROF_CC | PROF_HST | PROF_HW | PROF_HC);
    	bin_write_4bytes(&fout, p);
    
    	fout.close();
    }
    
    void load_breeds(ifstream *file, vector <breed*>*breedVector) // problem
    {
    	char c = file->get();
    
    	cout << static_cast<int>(c) << endl;
    }
    
    ifstream fin;
    
    fin.open("cdb.dat", ios::in | ios::binary); // starts it all
    load_breeds(&fin, &engine::breedVector);
    fin.close();

  5. #5
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    Code:
    void load_breeds(ifstream &fin);  // Function prototype
    
    load_breeds(fin); // Function call
    Last edited by SlyMaelstrom; 02-20-2006 at 05:22 PM.
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  6. #6
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    Code:
    enum PROF_MASK
    {
    	PROF_CNO = (1 << 0),
    	PROF_CS  = (1 << 1),
    	PROF_CTS = (1 << 2),
    	PROF_CA  = (1 << 3),
    	PROF_CTA = (1 << 4),
    	PROF_CM  = (1 << 5),
    	PROF_CTM = (1 << 6),
    	PROF_CP  = (1 << 7),
    	PROF_CST = (1 << 8),
    	PROF_CD  = (1 << 9),
    	PROF_CB  = (1 << 10),
    	PROF_CSH = (1 << 11),
    	PROF_CW  = (1 << 12),
    	PROF_CC  = (1 << 13),
    	PROF_CH  = (1 << 14),
    	PROF_CL  = (1 << 15),
    	PROF_HNO = (1 << 16),
    	PROF_HS  = (1 << 17),
    	PROF_HTS = (1 << 18),
    	PROF_HA  = (1 << 19),
    	PROF_HTA = (1 << 20),
    	PROF_HM  = (1 << 21),
    	PROF_HTM = (1 << 22),
    	PROF_HP  = (1 << 23),
    	PROF_HST = (1 << 24),
    	PROF_HD  = (1 << 25),
    	PROF_HB  = (1 << 26),
    	PROF_HSH = (1 << 27),
    	PROF_HW  = (1 << 28),
    	PROF_HC  = (1 << 29),
    	PROF_HH  = (1 << 30),
    	PROF_HL  = (1 << 31),
    };

  7. #7
    Devil's Advocate SlyMaelstrom's Avatar
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    Yes, I answered your question. Didn't see it right away. You aren't passing your ifstream correctly. Your other option is just to use the value of operator when you reference the stream.

    Code:
    *fin >> c;
    Though, I'll tell your that I wasn't able to compile the code you posted again, without making these changes. If you're saying you did compile it, you may be having a different problem. Regardless, you're referencing an incorrect stream and that may be cause you to read in an EOF.
    Last edited by SlyMaelstrom; 02-20-2006 at 05:27 PM.
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  8. #8
    Registered User Tonto's Avatar
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    Wait, are you reading this file before you write to this? Exact code. I believe you can pass ifstreams by pointer or by reference, just not by value.

  9. #9
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    Its still not working for me. If I see your post correctly you're telling me to pass it as a reference and not a pointer. I did that and it still won't work. And how would that change how it works anyways?

    No I am not writing to this file at all, I was simply showing the code that at one point wrote that file.

    *fin >> c does not work either. That reads a 0 and not a negitive 1.
    Last edited by yahn; 02-20-2006 at 05:34 PM.

  10. #10
    Devil's Advocate SlyMaelstrom's Avatar
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    Compile this:
    Code:
    #include <iostream>
    #include <fstream>
    
    using namespace std;
    
    void write() // writes the file i'm reading
    {
       ofstream fout;
       fout.open("cdb.dat", ios::out | ios::binary);
    	
       unsigned char c = 3;
       fout << c;
    
       fout.close();
    }
    
    void load(ifstream &fin)
    {
       unsigned char c;
       fin >> c;
       cout << static_cast<int>(c) << endl;
    }
    
    int main() 
    {
       ifstream fin;
    
       fin.open("cdb.dat", ios::in | ios::binary);
    
       write();
       load(fin);
    
       fin.close();
       
       return 0;
    };
    Sent from my iPadŽ

  11. #11
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    That works. Is it possibly because I am using the ifstream previous to when I open it?

  12. #12
    Devil's Advocate SlyMaelstrom's Avatar
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    Well, then there must have been something about "Post your exact code" that you didn't understand.
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  13. #13
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    So then do I need to use a seperate ifstream for every time I open a file?

  14. #14
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    Code:
    ifstream fin;
    
    fin.open("cdb.dat", ios::in | ios::binary); // starts it all
    load_breeds(&fin, &engine::breedVector);
    fin.close();
    Where is that code placed??

  15. #15
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    In a function thats called by a function in main.

    Code:
    int engine_init()
    {
    	sock_init();
    
    	ifstream fin;
    
    	engine::sock_listen = socket(PF_INET, SOCK_STREAM, 0);
    	engine::sock_accept = socket(PF_INET, SOCK_STREAM, 0);
    
    	// <-- start set fdset
    	FD_ZERO(&engine::playerSockets);
    
    	FD_SET(engine::sock_listen, &engine::playerSockets);
    	//FD_SET(engine::sock_accept, &engine::playerSockets);
    
    	engine::selectTime.tv_sec  = 0;
    	engine::selectTime.tv_usec = 0;
    	// end set fdset -->
    
    	// <-- start set server address
    	engine::addrServer.sin_family      = AF_INET;
    	engine::addrServer.sin_port        = htons(7869);
    	engine::addrServer.sin_addr.s_addr = htonl(INADDR_ANY);
    	// end set server address -->
    
    	// <-- start load item database
    	fin.open("idb.dat", ios::in | ios::binary);
    	load_items(&fin, &engine::itemVector);
    	fin.close();
    	// end load item database -->
    
    	// <-- start load breeds
    	fin.open("cdb.dat", ios::in | ios::binary);
    	load_breeds(&fin, &engine::breedVector);
    	fin.close();
    	// end load breeds  -->
    
    	if (bind(engine::sock_listen, (sockaddr *)&engine::addrServer, sizeof(engine::addrServer)) == SOCKET_ERROR)
    	{
    		WSACleanup();
    		return (0);
    	}
    
    	if (listen(engine::sock_listen, 1) == SOCKET_ERROR)
    	{
    		WSACleanup();
    		return (0);
    	}
    
    	return (1);
    }

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