Question

I’ve got a question concerning C programming.It is concerning binary files.In my code I(at least imagined that I) made it read and write from a binary file,but it won’t do that for some reason.I’ve tried changing some things but I just don’t see the error anywhere.And it is just this minimal detail which is giving me a hard time,it is all that is left to make in this code before it is done and then I’m done with the program altogether,so it gets on my nerves a bit more than it would usually.Please point out what it is I haven’t done and what i should do to make it read from and write to binary files properly:

 #define MAX 4

//========================-STRUCTURE-=====================================================================

struct person{

char name[30];
char mail[30];
char tele[30];

};

struct person p[MAX];

//========================-MAIN FUNCT-===============================================================
int main()
{

bool continue=true,exists=false;
int answer,i;
char filnme[20];

FILE *fil;

printf("Would you like to open an already existing file?[y/n]: ");
scanf("%d",&answer);
if(answer=='y'||answer=='Y')
{
    finns=true;
}
else finns=false;

getchar();

printf("\n\nType the name of the file you will use: ");
scanf("%s",filnme);

if(exists)
{

    fil = fopen(filnme,"rb");

    for(i=0;i<MAX;i++)
    {
        while(feof(fil)==0)
            {
            fread(&p, MAX, 1, fil);
            printf("%s %s %s\n",p.name,p.mail,p.tele);
        }

    }

    fclose(fil);
}

else fil = fopen(filnme,"wb");

do
{

    system("cls");

    int choice;

    printf("What would you like to do?");
    printf("\n_______________\n");
    printf("1. Add another person to the list\n");
    printf("2. Print the entire list\n");
    printf("3. Remove information from the list\n");
    printf("4. Sort\n");
    printf("5. Change information\n");
    printf("6. Search\n");
    printf("7. Exit\n");
    printf("\nChoice: ");
    scanf("%d",&choice);
    printf("\n");

    system("cls");

    switch(choice)
    {

        case 1:

        addtolist();
        getch();
        break;

        case 2:
        write();
        getch();
        break;

        case 3:
        remove();
        getch();
        break;

        case 4:
        sort();
        getch();
        break;

        case 5:
        change();
        getch();
        break;

        case 6:
        search();
        getch();
        break;

        case 7:
        continue=false;
        break;

        default:
        printf("Not a valid choice!");
        getch();
        break;

    }

}while(continue);

for(i=1;i<=MAX;i++)
{

        fwrite(&p, MAX, 1, fil);

}

fclose(fil);

system("cls");

}

Nevermind the declaration of functions or such,I’ve got that covered,just the binary file handling I put into the main.

Thanks in advance!

Answer 1

You are not using fread and fwrite correctly.

fread(&p, MAX, 1, fil);

should be:

fread(&p[i], sizeof(person), 1, fil);

Similarly for the fwrite call.

An alternative to calling fread and fwrite in a loop is to read/write the entire array in one go, like so:

fread(&p, sizeof(person), MAX, fil);