Memory Issues

This is a discussion on Memory Issues within the C Programming forums, part of the General Programming Boards category; Ok I don't really understand. Almost whenever I write a program that requires user input I get this error saying ...

  1. #1
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    Memory Issues

    Ok I don't really understand. Almost whenever I write a program that requires user input I get this error saying the program caused an error in MSVCRT.DLL and will now close. From previous experience, that is a memory error because of some memory issues. But the type of information the program is storing when it hits the error is int. Is it necessary to "allocate" memory for a int type too!? If someone could please explain this to me that would be a great help. Also, when storing a string, what is better to use? An array like this:
    Code:
    char array[5000];
    
    
    array[5000] = "This is a string";
    or a pointer like this:

    Code:
    char *pointer;
    
    
    pointer = (char*)malloc(5000);
    
    pointer = "This is a pointer";
    Thanks a bunch.

  2. #2
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    umm, you could try using strcpy (string copy) to set your array, becuase just doing this array[5000] = "this " will not work and that could be causing your program to crash becuase if have any other place where you are reading in data from the input buffer it will take what is not copied, unless you clear the buffer and your array will never have any valid data in it so , try this when setting an array

    strcpy(array, "This is a string");



    hope that helps you

  3. #3
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    when you are storing a string it is better to use the first method becuase if you ever want to change a string or find the length, etc it will be easier to do

  4. #4
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    Ok thanks. But about the first question.... Do you know why my program is crashing?

    I don't really understand. Almost whenever I write a program that requires user input I get this error saying the program caused an error in MSVCRT.DLL and will now close. From previous experience, that is a memory error because of some memory issues. But the type of information the program is storing when it hits the error is int. Is it necessary to "allocate" memory for a int type too!?

  5. #5
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    post your program or at least the part that you believe is causing the crash

  6. #6
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    Code:
    int main()
    {
    	char *name = (char*)malloc(50), *job = (char*)malloc(1000);
    	int id, info;
    
    	puts("Enter the ID:");
    	scanf("%d",id);
    
    	puts("Enter employee name:");
    	fgets(name,sizeof(name),stdin);
    
    	puts("Enter employee's duty:");
    	fgets(job,sizeof(job),stdin);
    
    	info = writeinfo(name,id,job); /* This function is contained in a header file of mine
    but I don't think it has anything to do with the error anyway */
    
    	if(info!=0)
    	{
    		puts("Operation Failed");
    		return 1;
    	}
    	else
    	{
    		puts("Success!");
    		return 0;
    	}
    }
    What's happening is that it gets to the part where it says "Enter the ID:" and when I enter any number whatsoever it causes the error and crashes.

  7. #7
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    okay try this, make your varibles arrays

    such as char name[50];

    and

    make sure you have at the top of your program

    #include<string.h>

    and

    change your fgets to read like this

    fgets(name);

    and

    try to have one return statement only, this requires an extra varible, but it's a good programming habit

    hope any of these suggestions helps you

  8. #8
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    Ok thanks. But what about that integer? It's int id that is causing the error. When scanf enters a value into it the program crashes.

  9. #9
    and the hat of wrongness Salem's Avatar
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    > fgets(name);
    It takes 3 parameters - the original calls were almost correct

    > fgets(job,sizeof(job),stdin);
    sizeof() on a pointer is the size of the pointer itself, not the amount of memory it points to

    Just stick with
    char job[50];
    fgets(job,sizeof(job),stdin);

    > scanf("%d",id);
    This probably explains all your crashes - you forgot the &
    as in
    scanf("%d", &id);

    But you'll want to ditch your use of scanf() if you're also using fgets()
    Use
    char buff[100];
    fgets( buff, sizeof buff, stdin );
    sscanf( buff, "%d", &id);
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  10. #10
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    Ahhhhh Salem. Thank you VERY much. Fixed all those pesky errors. And I can't believe I forgot the &! Show's I'm still new! There's one more little error I've been having... My code looks like this:
    Code:
    fprintf(file_ptr,"id: %d Name: %s Job: %s",id,name,job);
    It puts the info into the file properly but the file looks like this
    id: 100 Name: Test
    Job: Tester Master
    And I have no newline after the name part. So it's supposed to look like this:
    id: 100 Name: Test Job: Tester Master
    Also, one last thing, Just out of curiosity, when is it appropriate to use pointers to store strings? My book seemed to use them a lot but whenever it used them it got it right. Whenever I do, I mess it up. Thanks again.

  11. #11
    ... kermit's Avatar
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    Quote Originally Posted by Padawan
    There's one more little error I've been having... My code looks like this:
    Code:
    fprintf(file_ptr,"id: %d Name: %s Job: %s",id,name,job);
    It puts the info into the file properly but the file looks like this

    And I have no newline after the name part. So it's supposed to look like this:
    You have this:
    Code:
    puts("Enter employee name:");
    	fgets(name,sizeof(name),stdin);
    Did you try checking for the newline? Give this a try:

    Code:
    char *p;
    
    fgets(name, sizeof(name), stdin);
    if ((p = strchr(name, '\n')) != NULL) {	 /* check if last element is a newline */
        *p = '\0';		 	         /* if it is, make last element a null character */
    }
    Of course to use strchr(), you need to include string.h

    strchr() finds the first occurrence of the specified character, and returns a pointer to the instance of the character searched for in the string - if it finds nothing, it returns NULL. In this case, if it finds '\n' it returns a pointer to that character, which is then assigned to p. From there it is a matter of replacing '\n' with '\0'

    ~/

  12. #12
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    Thanks a lot kermit. That did it! How did the \n get there in the first place?

  13. #13
    ATH0 quzah's Avatar
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    You printed the newline in your file right? Well, it was there when it read it back in. Or in the event you're reading from the keyboard, you did hit enter, correct? Well fgets reads that in.

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

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