C problem - Create a Personal Library

Hello, I am new to the forums and I just have a quick question.

For the most part the program does what it needs to (which is print off
the list of what was added and what was removed based on my
file)

but I cannot figure out why it is crashing

here is my code

Code:

---

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

#define MAX_LENGTH 40
#define MAX_BOOKS 1000

//Make struct for book
struct book {
        char title[MAX_LENGTH];
        char author[MAX_LENGTH];
        char subject[MAX_LENGTH];
};

//Make struct for library
struct library {
        struct book collection[MAX_BOOKS];
        int num_books;
};       

//Create each of the functions
void copybook(struct book *dest, struct book *source);
void addBook(FILE *ifp, struct library *thislib, struct book b);
void removeBook(FILE *ifp, struct library *thislib, struct book *b);
void author_list(FILE *ifp, struct book *l, struct book *b, struct library *thislib);
void genre_list(FILE *ifp, struct book *l, struct book *b, struct library *thislib);
int searcher(struct book *b, struct book *l, struct library *thislib);
void printLib(struct book *l, int length);



int main (void) {
       
        struct book shelf;
        struct library myLib;
       
        FILE *ifp;
        ifp = fopen("library.txt", "r");
       
        int cases;
        fscanf(ifp, "%d", &cases);
       
        int instruct, i;
       
        for (i=0; i<cases; i++) {
                fscanf(ifp, "%d", &instruct);
                if (instruct == 1) {
                        addBook(ifp, &myLib, shelf);
                } else if (instruct == 2) {
                        removeBook(ifp, &myLib, &shelf);
                } else if (instruct == 3) {
                       
            int k = 0;
                        fscanf(ifp, "%s", &shelf.title[k]);
                        if (searcher(&shelf, myLib.collection, &myLib) == 1) {
                                printf("The book %s is currently in the library.\n\n", shelf.title);
                        } else {
                                printf("The book %s is NOT currently in the library.\n\n", shelf.title);
                        }
                } else if (instruct == 4) {
                        author_list(ifp, myLib.collection, &shelf, &myLib);
                } else {
                        genre_list(ifp, myLib.collection, &shelf, &myLib);
                       
                }
        }
        fclose(ifp);
        system("PAUSE");
    return 0;
}

//Function to copy book
void copybook(struct book *dest, struct book *source) {
        strcpy(dest->title, source->title);
        strcpy(dest->author, source->author);
        strcpy(dest->subject, source->subject);
}

//Function to add book
void addBook(FILE *ifp, struct library *thislib, struct book b) {
        fscanf(ifp, "%s%s%s", &b.title[thislib->num_books], &b.author[thislib->num_books], &b.subject[thislib->num_books]);
        copybook(thislib->collection, &b);
        thislib->num_books++;
        printf("The book %s has been added to the library.\n\n", b.title);
}

//Function to remove book
void removeBook(FILE *ifp, struct library *thislib, struct book *b) {
        int i;
        fscanf(ifp, "%s", &b->title[i]);
        for (i=0; i<thislib->num_books; i++) {
                if (searcher(thislib->collection, b, thislib) == 1) {
                }
        }
        thislib->num_books--;
        printf("The book %s has been removed from the library.\n\n", b->title);
}

//Function to search
int searcher(struct book *b, struct book *l, struct library *thislib) {
        int i;
        for (i=0; i<thislib->num_books; i++) {
                if (strcmp(b->title, l->title) == 0) {
                        return 1;
                }
        }
        return 0;
}

//Function to scan author
void author_list(FILE *ifp, struct book *l, struct book *b, struct library *thislib) {
        int i, count;
        fscanf(ifp, "%s", &b->author[i]);
        printf("List of all books by %s\n", b->author);
        for (i=0; i<thislib->num_books; i++) {
                if (strcmp(b->author, l->author) == 0) {
                        count++;
                        printf("%s\n", l->title);
                }
        }
}

//Function to scan genre
void genre_list(FILE *ifp, struct book *l, struct book *b, struct library *thislib) {
        int i, count;
        fscanf(ifp, "%s", &b->subject[i]);
        printf("List of all books on %s\n", b->subject);
        for (i=0; i<thislib->num_books; i++) {
                if (strcmp(b->subject, l->subject) == 0) {
                        count++;
                        printf("%s\n", l->title);
                }
        }
}

//Funtion to print list
void printLib(struct book *l, int length) {
        int i;
        for (i=0; i<length; i++) {
                printf("%s\n%s\n%s\n", l->title, l->author, l->subject);
        }
}

---

Can you at least indicate where it is crashing? Have you tried using a debugger? Even if you can't pin point the location at least describe how you are attempting to run the program, what input you are providing, etc.

Basically it is just running that exact code and using a file i made called library.txt as the input in dev c++, it prints off exactly what it is suppose to output...but 5 seconds later in suddenly does the "Library.c program has suddenly stopped working windows is checking for a solution" so I am not exactly sure where the problem is

Hmm. It's probably some memory issue, but we will have to pin point where the problem occurs. Can you post the content of your input file here as well, so we can see the control path more clearly?

yep

11
1 TOM_SAWYER TWAIN FICTION
1 Intro_to_C_Programming King Computer_Science
3 Huckleberry_Finn
1 Huckleberry_Finn TWAIN FICTION
1 Guns,Germs,Steel Diamond Anthropology
1 Java5.0 Cohoon Computer_Science
4 Twain
5 computer_science
5 Computr_Science
2 Intro_to_C_Programming
4 King


this is in the input file library.txt

Aight. Let me give it a try on my machine. I'll get back to you.

thanks

Code:

---

//Funtion to print list
void printLib(struct book *l, int length) {
        int i;
        for (i=0; i<length; i++) {
                printf("%s\n%s\n%s\n", l->title, l->author, l->subject);
        }
}

---

What is this supposed to do? It looks like you just print the same thing over and over again. What's the purpose of that? Did you mean this to print your library, and take a library as an argument instead?

Edit:

And this...

Code:

---

//Function to scan author
void author_list(FILE *ifp, struct book *l, struct book *b, struct library *thislib) {
        int i, count;
        fscanf(ifp, "%s", &b->author[i]);
        printf("List of all books by %s\n", b->author);
        for (i=0; i<thislib->num_books; i++) {
                if (strcmp(b->author, l->author) == 0) {
                        count++;
                        printf("%s\n", l->title);
                }
        }
}

---

Should really be something like this:

Code:

---

for( i = 0; i < thislib->num_books; i++ )
    if( strcmp( b->author, thislib->collection[ i ]->author ) )
        ...

---

You are passing a library, but never actually doing anything with it. Or maybe...

Code:

---

struct book *p = thislib->collection;
for( i = 0; i < thislib->num_books; i++, p++ )
    if( strcmp( b->author, p->author ) == 0 ) ...

---

Quzah.

Here is what I get in my console when running your code:

The program doesn't crash however there are some problems with your string manipulation.

Code:

---

The book TOM_SAWYER has been added to the library.

The book AIntro_to_C_Programming has been added to the library.

The book Huckleberry_Finn is NOT currently in the library.

The book HuHuckleberry_Finn has been added to the library.

The book HucGuns,Germs,Steel has been added to the library.

The book HuckJava5.0 has been added to the library.

List of all books by wain
List of all books on omputer_science
List of all books on omputr_Science
The book ntro_to_C_Programming has been removed from the library.

List of all books by ing

Process returned 0 (0x0)  execution time : 0.046 s
Press any key to continue.

---

Mine didn't even get that far
my friend is doing the same code...and I think
his isn't even showing two of the lines

As quzah indicated your print lib function is wrong. Also note that the strings are not correctly formed, presumably because of using %s in fscanf with the spaces that separate the inputs.

Ok....so fix the spaces around the %s...I am not sure exactly how to fix lib function
I am quite stupid when it comes to programming

your max length is 40 and if i counted right one of your titles is longer than 40.

I tried to change the max length...and it crashed without printing anything out

You have multiple bugs throughout your code. Another bug is in your remove_book function. You declare i, don't initialize it and then attempt to read title[i]. Solve this and then post your newly updated code so we can keep improving it.

Code:

---

struct book shelf;

---

The shelf stores one book?

Code:

---

        ifp = fopen("library.txt", "r");

---

You should be checking to see if your file failed to open or not before you try to use it.

Code:

---

        fscanf(ifp, "%d", &cases);

---

You should probably be reading entire lines at a time into a buffer with something like fgets instead, simply because it's cleaner to do so.

Code:

---

                fscanf(ifp, "%d", &instruct);

---

You should really be checking your return values to see if you get what you expect or not.

You might consider using a switch:

Code:

---

                if (instruct == 1) {
                        addBook(ifp, &myLib, shelf);
                } else if (instruct == 2) {
                        removeBook(ifp, &myLib, &shelf);
                } else if (instruct == 3) {
                       
            int k = 0;
                        fscanf(ifp, "%s", &shelf.title[k]);
                        if (searcher(&shelf, myLib.collection, &myLib) == 1) {
                                printf("The book %s is currently in the library.\n\n", shelf.title);
                        } else {
                                printf("The book %s is NOT currently in the library.\n\n", shelf.title);
                        }
                } else if (instruct == 4) {
                        author_list(ifp, myLib.collection, &shelf, &myLib);
                } else {
                        genre_list(ifp, myLib.collection, &shelf, &myLib);
                       
                }

---

To...

Code:

---

        switch( instruct )
        {
            case 1: addBook(ifp, &myLib, shelf); break;
            case 2: removeBook(ifp, &myLib, &shelf); break;
            case 3:
            {
                int k = 0;
                fscanf(ifp, "%s", &shelf.title[k]);
                if (searcher(&shelf, myLib.collection, &myLib) == 1) {
                    printf("The book %s is currently in the library.\n\n", shelf.title);
                } else {
                    printf("The book %s is NOT currently in the library.\n\n", shelf.title);
                        } break;
            case 4: author_list(ifp, myLib.collection, &shelf, &myLib); break;
            case 5: genre_list(ifp, myLib.collection, &shelf, &myLib); break;
            default: printf( "Invalid instruct: %d\n", instruct );
                }

---

Not always the preferred method, but suits this nicely.

Code:

---

//Function to add book
void addBook(FILE *ifp, struct library *thislib, struct book b) {
        fscanf(ifp, "%s%s%s", &b.title[thislib->num_books], &b.author[thislib->num_books], &b.subject[thislib->num_books]);
        copybook(thislib->collection, &b);
        thislib->num_books++;
        printf("The book %s has been added to the library.\n\n", b.title);
}

---

I would probably separate my file reading functions from my book adding functions. Also, you seem to have a great deal of that mixed up. You're passing struct book b by value, not pointer, so anything you do here is lost anyway--plus, this is just a single book, not a library. You're getting those confused again.


Quzah.

yes...for some reason once we started functions
in my class...I went to hell. It is so confusing for me,
and I don't even want to do this as a career. I wanted to
do game design art...but I have to take C for my major

Thanks for helping though guys

Quote:

---

Originally Posted by Harliqueen

yes...for some reason once we started functions
in my class...I went to hell. It is so confusing for me,
and I don't even want to do this as a career. I wanted to
do game design art...but I have to take C for my major

Thanks for helping though guys

---

Don't give up now! Finish this project. It won't take you that long and you will feel that your work has been rewarding. Everyone asks for help sometimes even experienced programmers.

Ok...well I changed the coding to what was suggested and now I have a problem with the

Code:

---

//Funtion to print list
void printLib(struct book *l, int length) {
        int i;
        for (i=0; i<length; i++) {
                printf("%s\n%s\n%s\n", l->title, l->author, l->subject);
        }
}

---

which I remember you guys saying was wrong

Well it depends what you are trying to do here. The main problem is that as it is, you are iterating around i and then printf-ing something completely unrelated to the iterator, so basically printing the same thing over and over again. What you want is to pass the book collection and print each book in that collection. (i.e. book[i]).

Functions are easy if you remember the difference between pointers and non-pointers: they are in effect the same thing.

Everything in C is a value. An 'int' holds a value that is just a number. A pointer to an integer also holds a number as its value, but that number represents a spot in memory.

How does this relate to functions? Functions take (optionally) arguments (read: values). This can mean two things:[code]void foo( int x );[code]This function takes an integer value as its argument. What does that mean?

Code:

---

int bar = 5;
...
foo( bar ); /* take the value that bar has, in this case five, and pass it to foo */
...
foo( 5 ); /* take the value 5 and pass it to foo */

---

In both of those function calls, the program copies (duplicates) the value passed as its argument, and sticks it in the variable x that is the argument to this function foo. In both cases, x is five.

The only difference is if we make that "value" be a memory address or not. And really the only reason that seems to matter is because of how you can get away with using it. Say we have a pointer:

Code:

---

int *p;

---

And it points some place.

Code:

---

p = &someSpotThatRepresentsAnInt;

---

If we actually knew what that address was, we could pass that value to the function:

Code:

---

void bar( int *x );
...
bar( p ); /* pass the value stored in p to bar */
...
bar( (int *) 0x1234 ); /* pass some value that happens to be a valid memory address to p instead */

---

In both cases, just like when you don't use a pointer, the only thing that actually happens to arrive at bar is a value. We just treat these values as if they are actual variables by dereferencing them. Basically we say "Hey, compiler, when I do this, go to this value, as a memory address, and give me what's there!"

That's really all you have to remember. Everything is passed as a value. Pointers are just like anything else, except you get to dereference them and say "give me what's there" or "go here and put this to that".


Quzah.

Quote:

---

Originally Posted by claudiu

Well it depends what you are trying to do here. The main problem is that as it is, you are iterating around i and then printf-ing something completely unrelated to the iterator, so basically printing the same thing over and over again. What you want is to pass the book collection and print each book in that collection. (i.e. book[i]).

---

so i basically need to get rid of the int i

Quote:

---

Originally Posted by Harliqueen

so i basically need to get rid of the int i

---

No. You are trying to print a whole library right? A library is made of a number of books. What you want to print in that function is the title and author of each book from what I gather. Right now you are printing the author and title of a single book, the one you pass as parameter. What you need to do is pass an array of books which is basically your myLib struct. Then iterate through the books[] in myLib using the i counter and print the info for each of them.

Code:

---


for(i = 0;i < MAX_LENGTH;i++)

 printf("%s %s", myLib->collection[i]->author, myLib->collection[i]->title);

---

Oh yea...ok I see what you mean now

Code:

---

void printLib(struct book *l, int length)

---

should that be changed to something like this

Code:

---

void printLib(struct library *l, int MAX_LENGTH)

---

Quote:

---

Originally Posted by Harliqueen

Code:

---

void printLib(struct book *l, int length)

---

should that be changed to something like this

Code:

---

void printLib(struct library *l, int MAX_LENGTH)

---

---

Correct. Only you don't actually need to pass MAX_LENGTH since that is part of a #define which makes it available throughout your entire code. The library pointer will sufice. Then you can call the function like so:

Code:

---


printLib(&myLib);
 /* myLib is of type struct library so &myLib is the address of that struct, thus of type struct library* */

---

Quote:

---

Originally Posted by Harliqueen

Code:

---

void printLib(struct book *l, int length)

---

should that be changed to something like this

Code:

---

void printLib(struct library *l, int MAX_LENGTH)

---

---

If you trust your data, you don't even need that.

Code:

---

void printLib( struct lib *l )
{
    if( l != NULL )
    {
        size_t x;
        for( x = 0; x < l->librarysize; x++ )
        {
            print out the parts of this book
        }
    }
}

---

If you don't, add in a:

Code:

---

        for( x = 0; x < l->librarysize && x < LIBRARYSIZE; x++ )

---

Since you've already got a #define for it some place.


Quzah.

ok...I changed it to this

Code:

---

void printLib(struct lib *l ) {
        int i;
        for(i = 0;i < MAX_LENGTH;i++)
    printf("%s %s", myLib->collection[i]->author, myLib->collection[i]->title);
        }
}

---

but its being retarded and not working

It might actually be myLib->collection[i].author and myLib->collection[i].title because collection[i] is not a pointer.

Also my mistake, you have to iterate until myLib->num_books since that is your book counter for the library. MAX_LENGTH is just the total number of possible books.

ok...what it is saying now is that there is a problem with the top line
(highlighting in red)

Code:

---

void printLib(struct lib *l ) {
        int i;
        for(i = 0;i < MAX_LENGTH;i++)
    printf("%s %s", myLib->collection[i]->author, myLib->collection[i]->title);
        }
}

---

Count the number of { and } in this post.


Quzah.

Another change needs to be done in your searcher function.

You want to search for a book in a given library. So you only need one book parameter and iterate through the library just like you did in the print function and compare the b.title book with myLib->collection[i].title to see if they are equal.

Quote:

---

Originally Posted by quzah

Code:

---

void printLib(struct lib *l ) {
        int i;
        for(i = 0;i < MAX_LENGTH;i++)
    printf("%s %s", myLib->collection[i]->author, myLib->collection[i]->title);
        }
}

---

Count the number of { and } in this post.


Quzah.

---

yea took out the extra one