File input/output question

This is a discussion on File input/output question within the C Programming forums, part of the General Programming Boards category; I have been slaving over this for hours. Why is the following code: Code: #include <stdio.h> struct players { char ...

  1. #1
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    File input/output question

    I have been slaving over this for hours. Why is the following code:

    Code:
    #include <stdio.h>
    
    
    struct players
    {
    	char name[100];
    	char position[100];
    	double points;
    	double steals;
    	double blocks;
    	double rebounds;
    };
    
    struct players nba[100];
    
    
    int main()
    {
    	FILE *ifp, *ofp;
    	char inputFile[100];
    	char outputFile[100];
    	int numberPlayers;
    	
    	printf("What is the name of the input file?\n");
    	scanf("%s", inputFile);
    
    	
    	printf("What is the name of the output file?\n");
    	scanf("%s", outputFile);
    	
    	ifp = fopen("players.txt", "r");
    	
    	fscanf(ifp, "%d", &numberPlayers);
    	
    	fclose(ifp);
    	fclose(ofp);	
    
    	return 0;
    }
    Returning this error:

    Code:
     0 [main] a 3060 handle_exceptions: Exception: STATUS_ACCESS_VIOLATION
      10000 [main] a 3060 stackdump: Dumping stack trace to a.exe.stackdump
    
     ----jGRASP cygwin wedge2: process died on signal 11.
     ----jGRASP: operation complete.
    I know it must be something simple that I'm doing, but I just cannot seem to figure it out. If you guys could help me I'd love you forever.

  2. #2
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    Your runtime error is probably caused by the following statement. It has no corresponding fopen statement.

    Code:
    fclose(ofp);

  3. #3
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    I took that out, I get the same error.

  4. #4
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    Your code runs fine for me when I comment out the offending statement. If I uncomment the offending statement, I get a runtime error.

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    It compiles, but when I run it (with the players.txt file that contains only "10") I get the error

  6. #6
    cwr
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    Did you check that the result of the fopen call was non-null? (that is, the file opened successfully)

    Bob is correct in that fclose(ofp) will result in undefined behaviour, since ofp has not been initialised.

  7. #7
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    I tried using "10" in players.txt and it works fine. The only other thing that comes to mind is that possibly the scanf's having a problem with the input variables. There may be some "junk" in these variables. So, you may want to clear them out prior to using them.

    Bob

    Code:
    char inputFile[100]= {0};
    char outputFile[100] = {0};

  8. #8
    cwr
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    The contents of inputFile and outputFile don't matter, since the OP used scanf on them to write to them before any other use.

    As I said above, there are two problems with the program that could cause problems:

    1. As you said, fclose(ofp); where ofp is not initialised.
    2. Not checking that the fopen was successful.

  9. #9
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    The ipf returns a 0. Is this considered null?

    I have the players.txt file in the same directory as the exe file. I know in visual basic it needs to be in a bin directory, is there something similar the that in C?
    Last edited by allplay; 11-14-2005 at 07:03 PM.

  10. #10
    cwr
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    Yes, it's NULL, which means the file didn't open successfully. When fopen fails, look at strerror(errno) to see why it failed. Example:
    Code:
    /* additional headers at the top */
    #include <string.h> /* for strerror */
    #include <errno.h> /* for errno */
    
    /* ... */
    
    ifp = fopen("player.txt", "r");
    if (ifp == NULL)
    {
        fprintf(stderr, "Could not open file, reason: %s\n", strerror(errno));
        exit(1);
    }

  11. #11
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    Sorry guys for waisting your time. Windows made the name players.txt.txt

    grrrr, I knew it was something stupid.

  12. #12
    cwr
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    Yup, Windows is pretty stupid. :-)

    Check the return anyway, like I suggested above, it's a good habit.

  13. #13
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    Thanks for your help. I'll put it in my program.

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