Thread: C Problem - Create a Personal Library

  1. #1
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    C Problem - Create a Personal Library

    Hello, I am new to the forum. I need help in debugging the program as it does not produce the expected output and I can't figure out where goes wrong. I haven't completed the whole program and I am working on it part by part.

    Here is my code:

    Code:
    #include <stdio.h>#include <stdlib.h>
    #include <string.h>
    
    
    struct book
    {
    	char *title;
    	char *author;
    	char *subject;
    };
    
    
    struct library
    {
    	struct book collection;
    	int num_books;
    	struct library *next;
    };
    
    
    typedef struct library lib;
    typedef lib *libPtr;
    
    
    void addBook(FILE *fPtr,libPtr *sPtr);
    void copybook(struct book *dest,struct book *source);
    void deleteBook(FILE *fPtr,libPtr *sPtr);
    void searchBook(FILE *fPtr,libPtr *sPtr);
    void listAuthor(FILE *fPtr,libPtr *sPtr);
    void listSubject(FILE *fPtr,libPtr *sPtr);
    
    
    int main()
    {
    	libPtr startPtr = NULL;
    	int choice;
    	FILE *fPtr;
    	fPtr = fopen("library.txt","r");
    	if (fPtr == NULL)
    	{
    		puts("File can't be loaded.\n");
    	}
    	else
    	{
    		while (!feof(fPtr))
    		{
    			fscanf(fPtr,"%d",&choice);
    			switch (choice)
    			{
    				case 1:
    					addBook(fPtr,&startPtr);
    					break;
    			}
    		}
    	}
    	fclose(fPtr);
    	return 0;
    }
    
    
    void addBook(FILE *fPtr,libPtr *sPtr)
    {
    	libPtr newPtr;
    	libPtr currentPtr;
    	libPtr previousPtr;
    	struct library *myLib;
    	myLib = (struct library *)malloc(sizeof(struct library));
    	myLib->collection.title = (char *)malloc(sizeof(50));
    	myLib->collection.author = (char *)malloc(sizeof(50));
    	myLib->collection.subject = (char *)malloc(sizeof(50));
    	fscanf(fPtr,"%s%s%s",myLib->collection.title,myLib->collection.author,myLib->collection.subject);
    	newPtr = malloc(sizeof(lib));
    	if (newPtr != NULL)
    	{
    		newPtr->collection = myLib->collection;
    		newPtr->next = NULL;
    		while (currentPtr != NULL)
    		{
    			previousPtr = currentPtr;
    			currentPtr = currentPtr->next;
    		}
    		if (previousPtr == NULL)
    		{
    			newPtr->next = *sPtr;
    			*sPtr = newPtr;
    		}
    		else
    		{
    			previousPtr->next = newPtr;
    			newPtr->next = currentPtr;
    		}
    	}
    	else
    	{
    		puts("No memory available.\n");
    	}
    }

  2. #2
    Registered User Kernelpanic's Avatar
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    Code:
    #include <stdio.h>#include <stdlib.h>
    #include <string.h>
    Your "#include" are wrong arranged.

    C Problem - Create a Personal Library-includefalsch2018-12-14_175451-jpg

    Better:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    If correct no warnings but nevertheless it will not run:

    C Problem - Create a Personal Library-include2_2018-12-14_175726-jpg

    Also gcc -Wall -pedantic . . . shows no warnings or errors. Something is absolute wrong . . . but what?

  3. #3
    C++ Witch laserlight's Avatar
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    I suggest that you get rid of this typedef:
    Code:
    typedef lib *libPtr;
    It isn't wrong in itself, but generally a typedef of a pointer can make it more confusing to reason about the pointer, so it is usually better only to typedef a pointer when it is an opaque pointer, i.e., in that context the pointer will not be dereferenced or involved in pointer arithmetic.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  4. #4
    Registered User Kernelpanic's Avatar
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    Quote Originally Posted by laserlight View Post
    I suggest that you get rid of this typedef:
    Code:
    typedef lib *libPtr;
    It isn't wrong in itself, but generally a typedef of a pointer can make it more confusing to reason about the pointer, . . .
    Now I have seen my mistake: the file "library.txt" was missing. But with it it won't work still.

    "library.txt"

    Programming Books
    The Wait Group
    Computer science
    Maybe the reason for that is was @laserlight wrote.

  5. #5
    and the hat of int overfl Salem's Avatar
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    Code:
    struct library
    {
        struct book collection;
        int num_books;
        struct library *next;
    };
    This makes no sense.
    You're saying each library consists of only one book.

    Think about it in terms of
    - a book (title, author, subject)
    - a shelf (a list of books of finite size)
    - a library (a list of shelves, as many as you need)
    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.

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