Thread: create a book library without linked lists

Hello! I need to create a book library using dynamic memory allocation and structs.
I started the program but having a hard time finishing it.. I don't really know how should i organize the program and what's missing in order to finish it.
i need to take the commends from a simulation file. and the compiling needs to be in GCC.

the simulation file looks like this:
#lines which starts with # you shall be able to ignore in your code
#1 is the add book operation id, BOOK ID, BOOK NAME,author,pages number, publish year, category
1,A250,Adventures of Huckleberry Finn,Mark Twain,120,1884,adventure
#2 operation id, book id
2,A250
#3 operation id, book id
3,A250
#4 operation id
4
#5 operation id, file name
5, C:\bookStorage.txt
#6 operation id, file name
6, C:\bookStorage.txt

explanation about each command:
1. add a book
2. delete a book
3.search a book by it's serial number
4. print out all the books
5.save the book library in a file
6. get the book library data from a file


this is what i did so far:

Code:

typedef struct{
	int serial;
	int pg_num;
	int y_published;
	char* name;
	char* author;
	char* category;
}Book;

typedef struct(
	Book* b;
	int book_num;
	int length;
}Book_Shelf;

typedef struct{
	int command_number;
	Book b;
	char* file_name;
}Command;

void set_command(command* c, char* str);

int main(int argc, char* argv[]){

	FILE* pf;
	char buffer[512];
	Command c;
	
	pf = fopen(argv[1], "r");
	
	fgets(buffer, 512, pf);
	while (buffer[0] == '#'){
		fgets(buffer, 512, pf);
	}
	
	set_command(c, buffer);
	
	command_execute(c);
	
	return 0;
	
}

void add_book(Book_Shelf* bs, Book* b){
	
	if (bs->book_num == bs->length){
		bs->length *= 1.5;
		bs->b = (Book*)realloc(bs->b, length*sizeof(Book));
		if(bs->b==NULL)
			exit2;

	}
	
	bs->b[book_num].serial = b->serial;
	/* ... */
	
	
}

char* get_next_word(char* str, int* index){

	int i, length = 0;
	char* temp_str;
	
	for (i = 0; (str[i] != ',') && (str[i] != '\0'); i++, length++);
	length++;

	temp_str = (char*)malloc(length);
	for (i = 0; i < length; i++){
		temp_str[i] = str[i];
	}
	temp_str[length] = '\0';
	
	*index = i;
	
	return temp_str;

}

void set_command(command* c, char* str){
	
	int i = 0;
	
	c->command_number = atoi(*(get_next_word(str+i, &i)));
	
	switch(c->command_number){
		case 1:{
			c->b.serial = get_next_word(str+i, &i);
			c->b.name = get_next_word(str+i, &i);
			c->b.author = get_next_word(str+i, &i);

		}
	}
}

Please re-edit your message so that your code is in code tags...
<< !! Posting Code? Read this First !! >>

Next please indicate specific areas you're having problems with or ask specific questions.

Most of us are happy to lend a hand with errant code but as a rule we don't write code for you...

Right off the bat... this isn't going to work...

Code:

typedef struct{
    int serial;
    int pg_num;
    int y_published;
    char* name;
    char* author;
    char* category;
}Book;

You have pointers to char in your struct... think about what happens when you write that struct to disk and then reload it...

When a struct is likely to end up in some storage medium you need to keep all of it's data inside itself... Like this...

Code:

typedef struct{
    int serial;
    int pg_num;
    int y_published;
    char name[64];          //-- make these big enough to store the longest string you're
    char author[64];        //    likely to encounter.
    char category[16];
}Book;

Maybe so, but working with arrays means you can get up and running a lot sooner.

When it all works, you can then (quite easily, and once only) translate each array into its char* equivalent with malloc.

Unless you're rock-solid on using malloc, this will give you a quicker working program you can develop further. Until then, use of malloc bugs will just frustrate your progress.

Also, you're only reading the first command with your main.

Code:

	while (fgets(buffer, 512, pf) != NULL ){
		if ( buffer[0] == '#' ) continue;
		set_command(c, buffer);
		command_execute(c);
	}

Originally Posted by limilou

but i need the names (strings) with dynamic allocation.. so i can get any name without wasting memory..

Believe me, you don't want to do that... The first time you try to write one of your book structs to disk then read it back, you will find out exactly why.

Moreover... consider that with the string inside the struct you are using exactly the number of characters indicated... char name[40] uses exactly 40 characters. But, with dynamic strings you have the overhead of the pointer... so with a pointer to 40 characters you are actually using 44 characters... only 4 of which will get written to the disk.