Write binary(struct) data to the file using fread, fwrite

NAME

       fread, fwrite - binary stream input/output

SYNOPSIS

#include <stdio.h>
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);

Note:

 3rd Argument is sizeof nmemb:
      nmemb -> number of size to be written into fiile.
              Eg: if 1 then only one node will be written into file.
                  if 2 then two nodes will be written into the file.

DESCRIPTION

• The function fread() reads nmemb elements of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.
• The function fwrite() writes nmemb elements of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

RETURN VALUE

• On  success, fread() and fwrite() return the number of items read or written.  This number equals the number of bytes transferred only when size is 1.
• If an error occurs, or the end of the file is reached, the return value is a short item count (or zero).
• fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which occurred.
• Note: To verify error need to use ferror() API, could not use return value.

Program:

 

/* Write binary(struct) data to the file using fread, fwrite
 * Check : http://velrajcoding.blogspot.in
 */

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

#define FILE_NAME       "binary_fil"
#define FILE_NAME_2     "binary_fil2"
#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

typedef struct node {
    int   value1;
    int   value2;
    char  name[64];
} node_t;

void display_node(node_t *node, char *msg)
{
    if (!node || !msg) {
        printf("Node or msg is null \n");
        return;
    }
    printf("Node %s Value 1:%d Value2:%d name:%s \n", msg, node->value1, node->value2, node->name);

    return;
}

int file_write_struct(node_t *node, const char *file, size_t num_node)
{
    FILE        *fp = NULL;

    if (!(fp = fopen(file, "w"))) {
        printf("Error in open an file, error no:%d:<%s> \n", errno, strerror(errno));
        return FALSE;
    }

    /*
     * 3rd Argument is sizeof nmemb:
     *     nmemb -> number of size to be written into fiile.
     *              Eg: if 1 then only one node will be written into file.
     *                  if 2 then two nodes will be written into the file.
     */
    fwrite(node, sizeof(node_t), num_node, fp);
    if (ferror(fp)) {
        printf("Error in write to the file, error no:%d:<%s> \n", errno, strerror(errno));
        return FALSE;
    }
    fclose(fp);

    return TRUE;
}

int file_read_struct(node_t *node)
{
    FILE        *fp = NULL;

    if (!(fp = fopen(FILE_NAME, "r"))) {
        printf("Error in open an file, error no:%d:<%s> \n", errno, strerror(errno));
        return FALSE;
    }

    fread(node, sizeof(node_t), 1, fp);
    if (ferror(fp)) {
        printf("Error in write to the file, error no:%d:<%s> \n", errno, strerror(errno));
        return FALSE;
    }
    fclose(fp);

    return TRUE;
}

int main()
{
    node_t      node[] = { {100, 200, "Velraj Kutralam"},
                           {20, 35, "Kutralam S"} };
    node_t      node_read = {0};

    display_node(node, "before save");
    file_write_struct(node, FILE_NAME, 1);
    file_write_struct(node, FILE_NAME_2, 2);

    file_read_struct(&node_read);
    display_node(node, "after save");

    return 0;
}

 

Output:

:~/velrajk/sample$ ./a.out
Node before save Value 1:100 Value2:200 name:Velraj Kutralam
Node after save Value 1:100 Value2:200 name:Velraj Kutralam
:~/velrajk/sample$ cat binary_fil
d▒Velraj Kutralam:~/velrajk/sample$
:~/velrajk/sample$ cat binary_fil2
d▒Velraj Kutralam#Kutralam S:~/velrajk/sample$

Vim of binary_fil:

d^@^@^@È^@^@^@Velraj Kutralam^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@

Vim of binary_fil2:

^@^@^@È^@^@^@Velraj Kutralam^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^T^@^@^@#^@^@^@Kutralam S^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@