fwrite() not working to write integer in binary file - c

Question

Can someone tell my why won't this function work? I just can't get it...
void writeRegister(FILE *arq, Book *L){ //writes in actual file position
char c = '|';
int sizeRegWrite = reglen(L); //reglen() returns the size of Book
fwrite(&sizeRegWrite, sizeof(int), 1, arq);
fwrite(L->TITLE, sizeof(char), strlen(L->TITLE), arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->AUTHOR, sizeof(char), strlen(L->AUTHOR), arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->PUBLISHER, sizeof(char), strlen(L->PUBLISHER), arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->YEAR, sizeof(int), 1, arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->LANGUAGE, sizeof(char), strlen(L->LANGUAGE), arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->PAGES, sizeof(int), 1, arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
fwrite(L->PRICE, sizeof(float), 1, arq);
fwrite(&c, sizeof(char), 1, arq); //writing delimiter
return;
}
The struct Book is declared like this:
typedef struct {
char *TITLE;
char *AUTHOR;
char *PUBLISHER;
int YEAR;
char *LANGUAGE;
int PAGES;
float PRICE;
} Book;
Main
int main() {
FILE *arq = fopen("BD_books2.bin", "rb+");
if(arq == NULL)
printf("Error while opening file!!!");
Book L;
readData(&L); //Reads all fields from keyboard and places in Book. Working properly
writeRegister(arq, &L);
system("pause");
return 0;
}
I have to use those pointers inside the struct, so I can't remove them. By the way, my problem is only with those integers and the float.
This fuction is only working properly if I write all the integers and floats (YEAR, PAGES and PRICE) with fprintf(), but I'm writing it in a binary file, and of course I want to write it in binary, so I'm trying to use fwrite().
Another thing is: the compiler is pointing incompatible type for argument 1 of 'fwrite' at this line: fwrite(L->PRICE, sizeof(float), 1, arq);
Can someone explain me what is happening? My program crashes when it tries to write in the file...

Answer 1

The first parameter of fwrite expects a pointer.
Lines such as the following:
fwrite(L->PAGES, sizeof(int), 1, arq);
Should be written as follows:
fwrite(&(L->PAGES), sizeof(int), 1, arq);
Sames goes for YEAR and PRICE members of that struct
fwrite(&(L->YEAR), sizeof(int), 1, arq);
...
fwrite(&(L->PRICE), sizeof(float), 1, arq);
Note, you don't need to make the same change for TITLE, PUBLISHER, and AUTHOR because the type of those member fields are already pointers (char*).

Answer 2

The signature of fwrite is
std::size_t fwrite( const void* buffer, std::size_t size, std::size_t count, std::FILE* stream );
The first argument to the function needs to be a pointer. I am surprised you didn't get compiler errors with the following lines.
fwrite(L->YEAR, sizeof(int), 1, arq);
fwrite(L->PAGES, sizeof(int), 1, arq);
fwrite(L->PRICE, sizeof(float), 1, arq);
They need to be
fwrite(&(L->YEAR), sizeof(int), 1, arq);
fwrite(&(L->PAGES), sizeof(int), 1, arq);
fwrite(&(L->PRICE), sizeof(float), 1, arq);
Also, it is a good practice to check the return values of all IO functions to make sure that they work as you expect them to.
if ( fwrite(&(L->YEAR), sizeof(int), 1, arq) != 1 )
{
// Deal with the error condition.
}

Answer 3

You must pass the address of L->YEAR to fwrite
fwrite(L->YEAR, sizeof(int), 1, arq);
fwrite(&(L->YEAR), sizeof(int), 1, arq);

Answer 4

the following code:
1) eliminates the bad practice of typedef'ing a struct
2) removed the mis-leading all caps of the struct field names
3) contains the needed #includes
4) contains the needed prototypes for the external (in another file) functions
5) checks for the worst of the many possible runtime errors
6) replaces the mis-leading 'L' with a meaningful name
7) modifies the file pointer variable to a commonly known name
suggest compiling with all warnings enabled (and fix the warnings)
for gcc, at a minimum, use '-Wall -Wextra -pednatic'
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Book
{
char *title;
char *author;
char *publisher;
int year;
char *language;
int pages;
float price;
};
int reglen( struct Book * );
int readData( struct Book * );
void writeRegister(FILE *fp, struct Book *myBook)
{ //writes in actual file position
char c = '|';
int sizeRegWrite = reglen(myBook); //reglen() returns the size of Book
fwrite(&sizeRegWrite, sizeof(int), 1, fp);
fwrite(myBook->title, sizeof(char), strlen(myBook->title), fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(myBook->author, sizeof(char), strlen(myBook->author), fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(myBook->publisher, sizeof(char), strlen(myBook->publisher), fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(&(myBook->year), sizeof(int), 1, fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(myBook->language, sizeof(char), strlen(myBook->language), fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(&(myBook->pages), sizeof(int), 1, fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
fwrite(&(myBook->price), sizeof(float), 1, fp);
fwrite(&c, sizeof(char), 1, fp); //writing delimiter
return;
} // end function: writeRegister
int main( void )
{
FILE *fp = fopen("BD_books2.bin", "rb");
if(fp == NULL)
{
perror( "fopen for BD_books2.bin failed" );
exit( EXIT_FAILURE );
}
// implied else, fopen successful
struct Book myBook;
int goodRead = readData(&myBook); //Reads all fields from keyboard and places in Book. Working properly
if( goodRead )
{
writeRegister(fp, &myBook);
}
system("pause");
return 0;
} // end function: main