fread creates a string with crap at the end

This is a discussion on fread creates a string with crap at the end within the C Programming forums, part of the General Programming Boards category; I want to read a whole text file a once into a single string. I have used the fread() function ...

  1. #1
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    fread creates a string with crap at the end

    I want to read a whole text file a once into a single string. I have used the fread() function in the following way:
    Code:
    #include <stdio.h>
    
    int main()
    {
    	FILE *fInp;
    	char buffer[1000];
    
    	fInp = fopen("input.txt", "r");
    	fread(buffer, 2, 1000, fInp);
    
    	printf("%s", buffer);
    
    	getchar();
    
    }
    My input.txt is:
    Code:
    i want to read that into a single string
    However it produces a string:
    Code:
    i want to read that into a single stringĚĚĚĚĚĚĚĚĚ<loads of identical crap>ĚĚĚĚĚĚĚĚĚĚĚĚhűbĚĚĚĚĚĚĚĚHűbĚĚĚĚ_=\ű
    How to get rid of that crap if i do not know beforehand how many characters are my input.txt?

  2. #2
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    fread returns number of items successfully. Read the doc!
    You need to null terminate('\0') at the end of your array to make it a C string. So that printf() and all other functions that operate on C string work properly.
    The second parameter of fread() is the size of each element, in this case sizeof(char) = 1.

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    Okay, I get that but how to find out in which place of my buffer array I need to put the null terminator?

  4. #4
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    He already told you. fread() returns the number of items read successfully. Check fread()'s return value and use it. Also, why are you using 2 for the second parameter to fread()? It should be 1.
    If you understand what you're doing, you're not learning anything.

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    Registered User whiteflags's Avatar
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    I would fix the fread call according to Bayint's advice first and see if it works. The only time you would need to insert one zero byte at the end would be if there wasn't one in the file already (or if you read a string of sufficient length greater than 1000) which I find strange.

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    Quote Originally Posted by itsme86 View Post
    He already told you. fread() returns the number of items read successfully. Check fread()'s return value and use it. Also, why are you using 2 for the second parameter to fread()? It should be 1.
    This is a typo, ofcourse it should be 1.

  7. #7
    Registered User whiteflags's Avatar
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    Oh wait, you're not even reading in binary mode. Use fgets instead of fread in that case.

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    fgets will read only one line of the file, what if there is more and i still want them all in one string?

    And that code below works, is that what you tried to tell me to fix?
    Code:
    #include <stdio.h>
    
    int main()
    {
    	FILE *fInp;
    	char buffer[1000];
    	int kutafon;
    
    	fInp = fopen("input.txt", "r");
    	kutafon = fread(buffer, 1, 1000, fInp);
    	buffer[kutafon] = '\0';
    	
    	printf("%s", buffer);
    
    	getchar();
    }
    Last edited by kulfon; 12-15-2010 at 09:18 AM.

  9. #9
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    Yes, But don't forget that you can't read 1000 all since you need to leave 1 more room for '\0'!
    Just imagine fread() reads 1000 chars, then return value will be 1000. buffer[1000] does not exist.(you don't own that space).
    kutafon should be declared as size_t.
    You might want to use feof(),ferror() to check if there's any error while reading file....

  10. #10
    Registered User whiteflags's Avatar
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    fgets will read only one line of the file, what if there is more and i still want them all in one string?
    Call fgets in a loop and concatenate all the strings together with say strncat, maybe?

  11. #11
    Registered User hellork's Avatar
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    I know this was just a learning exercise, but standard programming practice is to put the file-to-string conversion into a function and make it reusable. A rudimentary example function might take a file name and max size as arguments, check if file exists and is the required size, read it into an appropriately-sized dynamically-allocated buffer, check errors, and return a pointer to the buffer or error...

    Not sure about Windows, but POSIX also has memory-mapped I/O, functions that treat files as memory.

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