need a little help reading binary data in from a file

This is a discussion on need a little help reading binary data in from a file within the C Programming forums, part of the General Programming Boards category; ok this is gonna sound extremely dumb, but i have to ask. I have a binary data file and i ...

  1. #1
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    need a little help reading binary data in from a file

    ok this is gonna sound extremely dumb, but i have to ask. I have a binary data file and i want to open it to read it into my program using the fopen() function. Now its been a while since i used C, but i as i remember it the way to do this would be to put the following statement in to my code

    Code:
     
    fp=fopen("c:\test.bin", rb);
    where c:\test.bin is the address of the file i want to open. Yet when i compile my code i get this errors

    error C2065 : 'wb' : undeclared identifier

    error C4047: 'function' : 'const char*' differs in levels of direction from 'int'

    Can anybody give me any ideas what the problem is?

    Thanks in advance

    Andy

  2. #2
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    >fp=fopen("c:\test.bin", rb);
    Try:
    fp=fopen("c:\\test.bin", "rb");

    And it's always a good idea to check whether fopen() succeeded.

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    yeah, in my actual code i do check to make sure fopen worked thanks for the pointer though. Its been a while since i used C and im just testing ideas at the moment to get back into it, but as a second questions. If i input the following code
    Code:
    	char x[10]="ABCDEFGHIJ";
    	FILE *fp;
    	if((fp=fopen("c:\\test.bin", "wb"))==NULL)
    	{
                           printf("Couldnot open file");
                           exit(1);
                    }
    	fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), fp);
    
    	fcloseall();
    	return(0);
    should the file test.bin contain the binary version of ABCDEFGHIJ or should it show ABCDEFGHIJ if opened in notepad?

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    Quote Originally Posted by andydavenport
    yeah, in my actual code i do check to make sure fopen worked thanks for the pointer though. Its been a while since i used C and im just testing ideas at the moment to get back into it, but as a second questions. If i input the following code
    Code:
    	char x[10]="ABCDEFGHIJ";
    	FILE *fp;
    	if((fp=fopen("c:\\test.bin", "wb"))==NULL)
    	{
                           printf("Couldnot open file");
                           exit(1);
                    }
    	fwrite(x, sizeof(x[0]), sizeof(x)/sizeof(x[0]), fp);
    
    	fcloseall();
    	return(0);
    should the file test.bin contain the binary version of ABCDEFGHIJ or should it show ABCDEFGHIJ if opened in notepad?
    I don't know about you but I usually use types in sizeof

    Code:
     
                    int len = 10;
    	char x[len]="ABCDEFGHIJ";
    	FILE *fp;
    	if((fp=fopen("c:\\test.bin", "wb"))==NULL)
    	{
                           printf("Couldnot open file");
                           exit(1);
                    }
    	fwrite(x, sizeof(char), len, fp);
    
    	fcloseall();
    	return(0);

    and yes it will show ABCDEFGHIJ in notepad because you are printing ascii characters.

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    cheers

    i tell you blowing the cobebs outta the old brain is getting harder to do

  6. #6
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    Using types in sizeof is not required it's just something I prefer to do because it makes more sense when I read it.

  7. #7
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    ok, how do i get it to make the out put file into binary data, rather that ascii characters?

  8. #8
    ATH0 quzah's Avatar
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    Binary how? If you write the letter (character) 'a' in text mode, and all you're writing is that letter, it's going to be the same thing even if you open it in binary mode.The ascii values will still be the same in one mode or the next. As a matter of fact, there is no difference on most unix variants between text and binary modes.


    Quzah.
    Hope is the first step on the road to disappointment.

  9. #9
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by Brian
    I don't know about you but I usually use types in sizeof
    Whenever possible, I use sizeof with an actual object. Then if you ever change the object's type (from say a char to a wchar_t) there will be less code that needs additional changes. [And sizeof(char) is by definition 1.]
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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