Thread: problem with segmentation fault

Hi..everyone..i had trying to solve this problem but i really can't because i don't have any experience with C core dumped.Below is a program that can be compile but after exceution i get Segmentation fault (core dumped) with gcc (cygwin) compiler. Can anyone give me some piece of advice or tips.Thanks alot.

Code:

typedef struct bookStruct
{
   int id;
   char title[TITLE_LEN + 1];
   char author[AUTHOR_LEN + 1];
   int year;
   float price;
   int count;
   struct bookStruct* next;
} BookType;

typedef struct bookListStruct
{
   BookType* head;
   int count;
} BookListType;

BookType *b;
 
/* Function prototypes. */

void loadData(BookListType*, char*);
void displayBooks(BookListType*);

//int main(void)
int main(int argc, char *argv[])
{
 BookListType* booklist;
 int i;
 FILE *bookRead;
 char line[LINESIZE] , *word;
 
 if ( argc != 2 ) 
 {
    fprintf ( stderr, "Usage: %s <readfile1>\n", argv[0] );
    exit ( EXIT_FAILURE );
 }
  if((bookRead = fopen( argv[1], "r" )) == NULL)
 {
  fprintf(stderr, "cat: can't open %s\n", argv[1]);
 }
  
  loadData(booklist, argv[1]);
  displayBooks(booklist);
  fclose ( bookRead );
  return EXIT_SUCCESS;
}

void loadData(BookListType* booklist, char* booksFile)
{   
   char *delimeter = ":";
   char  *token, *bookPtr;
   char bookWord[100];
   BookType *b;
   FILE *bfile;
	/* fopen opens the file; exits if file cannot be opened */
	
	if ( ( bfile = fopen( booksFile, "r" ) ) == NULL ) 
	{
		fprintf(stderr,"***> Open error reading input file %s", booksFile);
		exit(-1);
	} 
	/* read all records from file (until eof) */
	while(!feof(bfile))
	{
	  while (bookPtr != NULL)
	   {
        if(fgets(bookWord,sizeof(bookWord),bfile)!=NULL) 
        {
 	      if (b = (BookType*)malloc(sizeof(BookType)))
           {   
            /*	copy the data from BookType to linked list	*/ 
            bookPtr = strtok(bookWord,delimeter);
            b->id=atoi(bookPtr);
		    strcpy(b->title, bookPtr);
		    strcpy(b->author, bookPtr);
		    b->year = atoi(bookPtr);
		    b->price = atof(bookPtr);
		    b->count = atoi(bookPtr);
            }
            bookPtr = strtok(NULL, delimeter);
         }    
            b->next = booklist->head;
            booklist->head = b;
            booklist->count++;       
	     }
        }
	fclose(bfile);
}
void displayBooks(BookListType* booklist)
{
     printf("ID  Title\t\t\t    Author\t Year\tPrice\tCount\n");
	printf("--  -----------------------------   ------------ ----\t-------\t-----\n");

	while(booklist->head!=NULL)
	{
		printf("%2d  %-32s%-12s%6d\t%2c%5.2f\t%4d\n", booklist->head->id,
			booklist->head->title, booklist->head->author, booklist->head->year,'$', 
			booklist->head->price,booklist->head->count);
		booklist->head = booklist->head->next;
	}
}

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define TITLE_LEN 20
#define AUTHOR_LEN 40
#define LINESIZE 300

typedef struct bookStruct {
    int id;
    char title[TITLE_LEN + 1];
    char author[AUTHOR_LEN + 1];
    int year;
    float price;
    int count;
    /*SaleType *head;*/
    struct bookStruct *next;
} BookType;

typedef struct bookListStruct {
    BookType *head;
    int count;
} BookListType;

/* unused - same name as a local variable */
/* BookType *b; */

/* Function prototypes. */

void loadData(BookListType *, char *);
void displayBooks(BookListType *);

int main(int argc, char *argv[])
{
    BookListType *booklist /* = NULL   uninitialised!! */;
    /*int i; is unused */
    FILE *bookRead;
    /*char line[LINESIZE], *word; is unused */

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <readfile1>\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    if ((bookRead = fopen(argv[1], "r")) == NULL) {
        fprintf(stderr, "cat: can't open %s\n", argv[1]);
    }

    /*!! calling this doesn't modify booklist in this scope */
    /* Try something like   booklist = loadData(argv[1]); */
    loadData(booklist, argv[1]);
    displayBooks(booklist);
    fclose(bookRead);
    return EXIT_SUCCESS;
}

void loadData(BookListType * booklist, char *booksFile)
{
    char *delimeter = ":";
    char /* unused *token, */ *bookPtr;
    char bookWord[100];
    BookType *b;
    FILE *bfile;
    /* fopen opens the file; exits if file cannot be opened */

    if ((bfile = fopen(booksFile, "r")) == NULL) {
        fprintf(stderr, "***> Open error reading input file %s",
                booksFile);
        exit(-1);
    }
    /* read all records from file (until eof) */
    while (!feof(bfile)) {  /*!! see the FAQ */
        while (bookPtr != NULL) { /* !! bookPtr starts off uninitialised */
            if (fgets(bookWord, sizeof(bookWord), bfile) != NULL) {
                /*!! don't cast malloc in C */
                if (b = (BookType *) malloc(sizeof(BookType))) {
                    /*  copy the data from BookType to linked list  */
                    bookPtr = strtok(bookWord, delimeter);
                    b->id = atoi(bookPtr);
                    strcpy(b->title, bookPtr);
                    strcpy(b->author, bookPtr);
                    b->year = atoi(bookPtr);
                    b->price = atof(bookPtr);
                    b->count = atoi(bookPtr);
                }
                bookPtr = strtok(NULL, delimeter);
            }
            b->next = booklist->head;
            booklist->head = b;
            booklist->count++;
        }
    }
    fclose(bfile);
}

void displayBooks(BookListType * booklist)
{
    printf("ID  Title\t\t\t    Author\t Year\tPrice\tCount\n");
    printf("--  -----------------------------   ------------ ----\t-------\t-----\n");

    while (booklist->head != NULL) {
        printf("%2d  %-32s%-12s%6d\t%2c%5.2f\t%4d\n", booklist->head->id,
               booklist->head->title, booklist->head->author,
               booklist->head->year, '$', booklist->head->price,
               booklist->head->count);
        booklist->head = booklist->head->next;
    }
}

There are many things wrong - mostly concerned with uninitialised pointers. These usually draw a segfault when you try and dereference them.

Something else to consider, try and simplify the code by not trying to do too much in a single function.
For example

Code:

BookType *ConvertData( char *buff ) {
    BookType *node = malloc ( sizeof *node );
    if ( node ) {
        /* do whatever to extract data */
        sscanf( buff, "%d", &node->id );
    }
    return node;
}

BookListType *booklist loadData ( char *booksFile ) {
    BookListType *result = NULL;
    char buff[BUFSIZ];
    FILE *fp = fopen( booksFile, "r" );
    while ( fgets( buff, BUFSIZ, fp ) != NULL ) {
        BookType *node = ConvertData( buff );
        result = ListAppend( result, node );
    }
}

Each function does one specific task.

Originally Posted by Kleid-0

No need to strtok(), you can use time_t, it's a long integer.

Don't assume too much. I would find too much wiggle room with "arithmetic type[s] capable of representing times".

Why not just
char date[11];
until you know what you need to do with date.

If you want to convert it to struct tm, or anything else later on, then you can still do that.
But for now, a string is good enough IMO

No - you use mktime() to create a time_t

Originally Posted by Kleid-0

Hey Dave,
time_t is usually a long integer. But either way you'd probably still be using atol() to convert the string Unix timestamp to the long number that will be placed into a time_t variable (that will, I believe, be some sort of integer).

Usually is not always.
Probably is not as good as a sure thing.

Quzah.

Why would you even bother, given that there are routines to pack and unpack a time_t variable.
Even if you assume it is an integral type, you still have to then assume that it contains seconds.

The standard merely states that time_t is an arithmetic type.