Trouble with DMA Segmentation Faults

This is a discussion on Trouble with DMA Segmentation Faults within the C Programming forums, part of the General Programming Boards category; This is my first time using dynamic memory allocation, and I've been having some problems with segmentation faults being thrown ...

  1. #1
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    Trouble with DMA Segmentation Faults

    This is my first time using dynamic memory allocation, and I've been having some problems with segmentation faults being thrown in my current program when I start calling different functions repeatedly (it is a simple e-mail database that prints, search, adds, deletes, etc, but when I say...print, add, delete, and then call search, search will throw a fault, whereas if I call search from the beginning, it runs without a glitch). Anyone have any clue what the problem is? I think it might have something to do with passing the mail structure pointer or perhaps freeing memory (if I run several functions many times, the numbers stored in each entry in the mail pointer array start getting weird), but I've tried everything and am stumped.

    In addition, I'm having trouble getting the sort function to work. I'm pretty sure the algorithm is correct, as it's simple bubblesort, and I've tested it with structures in main before, but for some reason, it refuses to sort correctly here. It doesn't seem to recognize and switch things correctly, though it loops all the way through. Again, any help would be appreciated. I'm a bit desperate at this point, as I've tried everything.

    Code:
    #include <stdio.h>
    #include <string.h>
    
    int size = 0;
    
    // Mail structure to store each e-mail's information
    struct mail {
        int timeindex;
        char month[4];
        int date;
        char *email;
        int msgsize;
        char *subject;
    };
    
    // Prints out e-mails in order currently stored in pointer 
    void print(struct mail * m1)
    {
        int i;
        for(i = 0; i < size; i++)
        {
    	printf("%3d ", i + 1);
    	printf("%s ", (m1 + i) -> month);
    	printf("%d ", (m1 + i) -> date);
    	printf("%s ", (m1 + i) -> email);
    	printf("%d ", (m1 + i) -> msgsize);
    	printf("%s\n", (m1 + i) -> subject);
        }
    }
    
    // Sorts emails in ascending order by received time, sender, or message size
    void sort(struct mail * m1)
    {
        int choice, i, pos;
        struct mail key;
    
        printf("***Sort Menu***\n");
        printf("1. Sort by received time\n");
        printf("2. Sort by sender\n");
        printf("3. Sort by size\n");
    
        // Read in user choice
        do {
    	printf("Please enter your choice (1-3): ");
    	scanf("%d", &choice);
        } while(choice < 1 || choice > 3);
    
        // Sort in ascending order by time message was received
        if(choice == 1)
        {
    	for(i = 0; i < size; i++)
    	{
    	    for(pos = i; pos < size; pos++)
    	    {
    		if((m1 + i) -> timeindex > (m1 + pos) -> timeindex)
    		{
    		    key = *(m1 + i);
    		    *(m1 + i) = *(m1 + pos);
    		    *(m1 + pos) = key;
    		}
    	    }
    	} 
        }
    
        // Sort alphabetically by sender e-mail 
        else if(choice == 2)
        {
    	for(i = 0; i < size; i++)
    	{
    	    for(pos = 0; pos < size; i++)
    	    {
    		if(strcmp((m1 + i) -> email, (m1 + pos) -> email) > 0)
    		{
    		    key = *(m1 + i);
    		    *(m1 + i) = *(m1 + pos);
    		    *(m1 + pos) = key;
    		}
    	    }
    	}
    
        }
    
        // Sort in ascending order by message size
        else if(choice == 3)
        {
    	for(i = 0; i < size; i++)
    	{
    	    for(pos = i; pos < size; pos++);
    	    {
    		if((m1 + i) -> msgsize > (m1 + pos) -> msgsize)
    		{
    		    key = *(m1 + i);
    		    *(m1 + i) = *(m1 + pos);
    		    *(m1 + pos) = key;
    		}
    	    }
    	}
        }
    }
    
    void add(struct mail * m1)
    {
        int i, space, check = 0;
        int dtemp, stemp;
        char ch, mtemp[4];
        char *sendtemp = malloc(20 * sizeof(char));
        char *subtemp = malloc(300 * sizeof(char));
        struct mail * m1temp;
    
        // Read in month (must be legal three-letter abbreviation)
        do {
    	printf("the month the message is received (format: mmm): ");
    	scanf("%s", mtemp);
        } while(strcmp(mtemp, "Jan") != 0 && strcmp(mtemp, "Feb") != 0 && 
    	    strcmp(mtemp, "Mar") != 0 && strcmp(mtemp, "Apr") != 0 && 
    	    strcmp(mtemp, "May") != 0 && strcmp(mtemp, "Jun") != 0 && 
    	    strcmp(mtemp, "Jul") != 0 && strcmp(mtemp, "Aug") != 0 && 
    	    strcmp(mtemp, "Sep") != 0 && strcmp(mtemp, "Oct") != 0 && 
    	    strcmp(mtemp, "Nov") != 0 && strcmp(mtemp, "Dec") != 0);
    
        // Read in date (must be 1 through 31)
        do {
    	printf("the day the message is received (format: d or dd): ");
    	scanf("%d", &dtemp);
        } while(dtemp < 1 || dtemp > 31);
    
        // Read in size of message (must be positive integer)
        do {
    	printf("the size of the message (format: integer): ");
    	scanf("%d", &stemp);
        } while(stemp < 0);
    
        // Read in sender e-mail (must be single string, no spaces)
        do {
    	space = 0;
    	printf("the sender of the message (format: no spacing): ");
    	scanf("%s", sendtemp);
    
            // Check to make sure entry is only one string
    	while(getchar() != '\n')
    	    space++;
        } while(space > 0);
    
        // Read in subject title character by character into a pointer string
        i = 0;
        printf("the subject of the message (format: no restriction): ");
        ch = getchar();
        while(ch != '\n')
        {
    	*(subtemp + i) = ch;
    	i++;
    	ch = getchar();
        }
    
        // Check to make sure entry is not identical to another entry in database
        for(i = 0; i < size; i++)
        {
    	if(strcmp(mtemp, (m1 + i) -> month) == 0 && 
    	   dtemp == (m1 + i) -> date && 
    	   stemp == (m1 + i) -> msgsize && 
    	   strcmp(sendtemp, (m1 + i) -> email) == 0 && 
    	   strcmp(subtemp, (m1 + i) -> subject) == 0)
    	    check = 1;
        }
    
        // If entry is not identical, add to end of database and update size
        if(check == 0)
        {
    	m1 = (struct mail *) realloc(m1, (size + 1) * sizeof(m1temp));
    	(m1 + size) -> timeindex = size + 1;
    	for(i = 0; i < 4; i++)
    	    (m1 + size) -> month[i] = mtemp[i];
    	(m1 + size) -> date = dtemp;
    	(m1 + size) -> msgsize = stemp;
    	(m1 + size) -> email = sendtemp;
    	(m1 + size) -> subject = subtemp;
    	size++;
    	printf("The message has been added successfully.\n");
        }
        // If entry already in database, print out failure message
        else
    	printf("Message add fails. The message exists in the database.\n");
    }
    
    void delete(struct mail * m1)
    {
        int i, index;
        // Read in index for deletion
        do {
            printf("Enter the index of the message to delete (1 to %d): ", 
    	       size);
            scanf("%d", &index);
        } while(index < 1 || index > size);
    
        // Shift all entries after index to the left by one
        for(i = index - 1; i < size - 1; i++)
    	*(m1 + i) = *(m1 + i + 1);
    
        // Free last memory location and update size
        free(m1 + size - 1);
        size--;
    
        printf("Message has been deleted successfully. ");
        printf("There are %d messages left.\n", size);
    }
    
    void search(struct mail * m1)
    {
        char *s1;
        int i, k, check, count = 0;
        printf("Enter the keyword that you want to search: ");
        scanf("%s", s1);
    
        // Loop through entire e-mail database pointer array    
        for(i = 0; i < size; i++)
        {
    	check = 0;
    	k = 0;
    
            // While current entry's subject is not at end of string, compare each
            // individual word to the keyword
    	while((m1 + i) -> subject[k] != '\0')
    	{
    	    int j = 0;
                // Increment indices while characters in both strings are equal 
                // and not at end of subject string
    	    while(s1[j] == (m1 + i) -> subject[k] && 
    		  (m1 + i) -> subject[k] != '\0')
    	    {
    		j++;
    		k++;
    	    }
    
                // If length of keyword is equal to j (all characters of word 
                // match) and it is the end of the currently checked word in 
                // entry's subject string, increment check
    	    if(strlen(s1) == j && ((m1 + i) -> subject[k] == ' ' || 
    				   (m1 + i) -> subject[k] == '\0'))
    		check++;
    
                // Increment subject index until beginning of next word in string
    	    while((m1 + i) -> subject[k] != ' ' && 
    		  (m1 + i) -> subject[k] != '\0')
    		k++;
    	    if((m1 + i) -> subject[k] == ' ')
    		k++;
    	}
    
            // If check is larger than 1, print out entry keyword was in
    	if(check > 0)
    	{
    	    printf("%3d ", i + 1);
    	    printf("%s ", (m1 + i) -> month);
    	    printf("%d ", (m1 + i) -> date);
    	    printf("%s ", (m1 + i) -> email);
    	    printf("%d ", (m1 + i) -> msgsize);
    	    printf("%s\n", (m1 + i) -> subject);
    	    count++;
    	}
        }
    
        // If keyword not found in any entries, print out keyword not found
        if(count == 0)
    	printf("Keyword %s not found.\n", s1);
    }
    
    // Print leave message and exit out of program
    void leave()
    {
        printf("Thanks for using the ENEE 114 Email Database.\n");
        printf("Goodbye!\n");
        exit(0);
    }
    
    int main(int argc, char *argv[])
    {
        int i, choice;
        char ch, temp;
        FILE *input;
        struct mail *m1, m2;
    
        // Allocate dynamic memory for mail pointer array
        m1 = (struct mail *) malloc(sizeof(m2));
    
        // If not enough arguments in command line, print out error
        if(argc != 2)
        {
    	printf("Usage: executable input_file\n");
    	exit(0);
        }
    
        input = fopen(argv[1], "r");
    
        // Check to make sure input file opened correctly
        if(input == NULL)
        {
    	printf("File %s cannot open!\n", argv[1]);
    	exit(0);
        }
    
        // Store input file e-mail information into mail database pointer array
        while(fscanf(input, "%c", &temp) != EOF)
        {
    	i = 0;
    
            // Store time index to indicate when message was added
    	(m1 + size) -> timeindex = size + 1;
    
            // Store month abbreviation in character by character
    	(m1 + size) -> month[0] = temp;
    	fscanf(input, "%c", &((m1 + size) -> month[1]));
    	fscanf(input, "%c", &((m1 + size) -> month[2]));
    	(m1 + size) -> month[3] = '\0';
    
            // Store date in
    	fscanf(input, "%d", &((m1 + size) -> date));
    
            // Allocate memory for e-mail string and store string
    	(m1 + size) -> email = malloc(20 * sizeof(char));
    	fscanf(input, "%s", (m1 + size) -> email);
    
            // Store message size in
    	fscanf(input, "%d", &((m1 + size) -> msgsize));
    
            // Skip blank space
    	fscanf(input, "%c", &ch);
    
            // Allocate memory for subject string and store in character by 
            // character until at end of current line
    	(m1 + size) -> subject = malloc(300 * sizeof(char));
    	while(fscanf(input, "%c", &ch) != EOF && ch != '\n')
    	{
    	    *((m1 + size) -> subject + i) = ch;
    	    i++;
    	}
    
            // Update size and reallocate mail pointer to larger memory location
    	size++;
    	m1 = (struct mail *) realloc(m1, (size + 1) * sizeof(m2));
        }
    
        // Display menu and call appropriate function for entered choice
        printf("Welcome to ENEE 114 Email Database\n");
        do {
            printf("***Main Menu***\n");
            printf("1. Print\n");
            printf("2. Sort\n");
            printf("3. Add Message\n");
            printf("4. Delete Message\n");
            printf("5. Keyword Search\n");
            printf("6. Exit\n");
            printf("\nPlease enter your choice (1-6): ");
    	scanf("%d", &choice);
    
    	switch(choice)
    	{
    	    case 1: print(m1); break;
    	    case 2: sort(m1); break;
    	    case 3: add(m1); break;
    	    case 4: delete(m1); break;
    	    case 5: search(m1); break;
    	    default: leave(); break;
    	}
        } while(choice != 6);
    
        free(m1);
        free(m2);
        fclose(input);
    
        return 0;
    }
    Last edited by firestorm717; 05-08-2006 at 11:12 AM.

  2. #2
    int x = *((int *) NULL); Cactus_Hugger's Avatar
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    1) You don't need to cast the result of malloc().
    2) You don't appear to free() the subject member of your mail structure, ever.
    3) You're using fscanf() to read single characters? Depending on your file's structure, perhaps fgetc() would be a better alternative?

    None of the things I've listed (except 3, but I can't find where) would cause a segfault. To aid in this forum helping you, where does said segfault occur? (Hint: Use a debugger!)

    Edit:
    In delete():
    Code:
        // Free last memory location and update size
        free(m1 + size - 1);
    You cannot free() that. You can free() all of m1 with free(m1) but free doesn't know anything about m1 + size - 1.
    Quote Originally Posted by man free
    free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc()
    m1 + size - 1 doesn't fit that condition. To remove the last item, you can realloc() m1 to be 1 structure smaller. (Also, don't forget to check return codes from malloc/realloc for NULL, as that will cause a segfault.)

    Code:
        if(check == 0)
        {
    	m1 = (struct mail *) realloc(m1, (size + 1) * sizeof(m1temp));
    m1 is of type struct mail *. First: m1temp is only used in this sizeof() statement. Instead of the variable, you can simply name the type: sizeof(struct mail). Also: m1temp is of type struct mail *, probably not correct for this call to realloc().
    Last edited by Cactus_Hugger; 05-07-2006 at 08:40 PM.
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
    The best way to accelerate an IBM is at 9.8 m/s/s.
    recursion (re - cur' - zhun) n. 1. (see recursion)

  3. #3
    Registered User
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    Thanks for the quick response. I've fixed the errors that you mentioned, but I'm not sure what you mean by freeing the subject variable. When I free the mail file structure, doesn't that automatically free everything else within it?

    I still get a segmentation fault at certain intervals. One such case is when I try to sort by message size, then print. I've found the error with the alphabetizing of e-mails, so that's working now.
    Last edited by firestorm717; 05-08-2006 at 11:13 AM.

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