Strange question mark at EOF

This is a discussion on Strange question mark at EOF within the C Programming forums, part of the General Programming Boards category; I made a simple program that reads a file and prints the contents of the file to the output. Code: ...

  1. #1
    Third Eye Babkockdood's Avatar
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    Strange question mark at EOF

    I made a simple program that reads a file and prints the contents of the file to the output.

    Code:
    #include <stdio.h>
    
    int main(int argc, char *argv[])
    {
    	if (!argv[1])
    	{
    		printf("USAGE: %s [filename]\n", argv[0]);
    		return 1;
    	}
    	
    	FILE *in = (fopen(argv[1], "r"));
    	char *file;
    	while (file != EOF)
    	{
    		file = fgetc(in);
    		printf("%c", file);
    	}
    	printf("\n");
    	return 0;
    }
    It prints the file contents to the output like it should, but there's a strange question mark at the end of it. I typed, ./prog foobar into the Terminal and it printed the following.
    Code:
    Hello World!
    ?
    There is no question mark at the end of the foobar file. Is it printing the terminating null byte? Can someone explain this to me?

  2. #2
    MTK
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    Quote Originally Posted by Babkockdood View Post
    char *file;
    while (file != EOF)
    BAD!!!

    You cannot use a "char" because each byte in the file fills a whole "char". How do you think the EOF can be represented then? You have to use an int instead. It's filled with the values 0-255 for a byte from the file, and a -1 for EOF.

    And why is the char a pointer?

    Also, you check if the file reached EOF before getting the next byte and printing it. You have to check between the reading of the byte and the printing. In your current code, the char isn't EOF, you read it, it's and EOF, but you brint it before checking!

    Here's the correct code:

    Code:
    int file;
    while (file = fgetc(in))
    {
            putchar(file);
    }
    Last edited by MTK; 06-08-2010 at 07:19 PM.

  3. #3
    Third Eye Babkockdood's Avatar
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    Quote Originally Posted by MTK View Post
    BAD!!!

    You cannot use a "char" because each byte in the file fills a whole "char". How do you think the EOF can be represented then? You have to use an int instead. It's filled with the values 0-255 for a byte from the file, and a -1 for EOF.

    Also, you check if the file reached EOF before getting the next byte and printing it. You have to check between the reading of the byte and the printing.
    OK, I made file an int and removed the asterisk. I'm not getting the same warning I was earlier, but it's still printing the question mark.

  4. #4
    Third Eye Babkockdood's Avatar
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    Quote Originally Posted by MTK View Post
    Here's the correct code:

    Code:
    int file;
    while (file = fgetc(in))
    {
            putchar(file);
    }
    I saw your edited post, and replaced the old code with the above. It was an endless loop that printed only question marks. I got it working. This is what I used.
    Code:
    int file;
    	while ((file = fgetc(in)) != EOF)
    	{
    		putchar(file);
    	}
    Thanks for pointing that out, MTK.

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    I wonder what compiler you are using.
    and how could you ignore all your compiler warnings (if there is any?)

  6. #6
    MTK
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    Quote Originally Posted by Babkockdood View Post
    Code:
    int file;
    	while ((file = fgetc(in)) != EOF)
    	{
    		putchar(file);
    	}
    Yeah, that's correct. Without the "!= EOF" part it checks if it's not 0 instead of not EOF (probably -1).

    And as you see the assignment operator can be used within an expression! It assigns the value to the right to the variable on the left, and evaluates to the new value of the variable.

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