fwrite（）無法在二進制文件中寫入整數

Question

有人可以告訴我為什么該功能不起作用嗎？ 我就是不明白...

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;
}  

結構書的聲明如下：

typedef struct {
    char *TITLE;
    char *AUTHOR;
    char *PUBLISHER;
    int YEAR;
    char *LANGUAGE;
    int PAGES;
float PRICE;
} Book;

主要

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;

}

我必須在結構中使用這些指針，因此無法刪除它們。 順便說一句，我的問題僅在於那些integers和float 。

僅當我使用fprintf()編寫所有整數和浮點數（YEAR，PAGES和PRICE）時，此功能才能正常工作，但我將其寫入二進制文件中，當然我想將其寫入二進制文件中，所以我正在嘗試使用fwrite（）。

另一件事是：編譯器在此行指向incompatible type for argument 1 of 'fwrite' ： fwrite(L->PRICE, sizeof(float), 1, arq);

有人可以解釋我發生了什么事嗎？ 當我嘗試寫入文件時，我的程序崩潰了。

Answer 1

fwrite的第一個參數需要一個指針。

如以下行：

fwrite(L->PAGES, sizeof(int), 1, arq);

應該寫成如下：

fwrite(&(L->PAGES), sizeof(int), 1, arq);

該結構的YEAR和PRICE成員都一樣

fwrite(&(L->YEAR), sizeof(int), 1, arq);
...
fwrite(&(L->PRICE), sizeof(float), 1, arq);

注意，您不需要對TITLE，PUBLISHER和AUTHOR進行相同的更改，因為這些成員字段的類型已經是指針（char *）。

Answer 2

fwrite的簽名是

std::size_t fwrite( const void* buffer, std::size_t size, std::size_t count, std::FILE* stream );

該函數的第一個參數必須是一個指針。 我很驚訝您沒有收到以下幾行的編譯器錯誤。

fwrite(L->YEAR, sizeof(int), 1, arq);
fwrite(L->PAGES, sizeof(int), 1, arq);
fwrite(L->PRICE, sizeof(float), 1, arq);

他們需要

fwrite(&(L->YEAR), sizeof(int), 1, arq);
fwrite(&(L->PAGES), sizeof(int), 1, arq);
fwrite(&(L->PRICE), sizeof(float), 1, arq);

同樣，最好檢查所有IO函數的返回值，以確保它們按預期工作。

if ( fwrite(&(L->YEAR), sizeof(int), 1, arq) != 1 )
{
   // Deal with the error condition.
}

Answer 3

您必須通過地址L->YEAR到fwrite

fwrite(L->YEAR, sizeof(int), 1, arq);

fwrite(&(L->YEAR), sizeof(int), 1, arq);

Answer 4

以下代碼：

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