Weird characters saved in my text file

Question

I'm trying to make a program that can store certain information in a text file. The problem I have though is that with the code I've written so far, the information stored is a bunch of weird symbols and characters. I've managed to kind of find out where it happens from but I can't seem to solve it. It seems like in my register_item function, both item number and balance get weird values for some reason. If anyone can see what mistake I've made, that would be appreciated.

    #include <stdio.h>
    #include <conio.h>
    #include <string.h>
    #include <stdlib.h>

    #define MAX 20

    struct vara
    {
        int itemnumber[20];
        char name[30];
        int balance[20];
    };

    open_file(FILE *ange_filnamn, char filnamn[], struct vara varor[], int *antal_varor)
    {
        int mainmenu = 0;
        while (mainmenu != 1 && mainmenu != 2)
        {
            printf("Do you want to open an existing file (1) or create a new one (2)?\n");
            scanf("%d", &mainmenu);
            //system("CLS");
            if(mainmenu==1)
            {
                printf("Choose filename (ex. .txt).\n");
                scanf("%s", filnamn);
                ange_filnamn=fopen(filnamn, "r+");         

                while(!feof(ange_filnamn))
                {

                    fread(&varor[*antal_varor], sizeof(struct vara), 1, ange_filnamn);
                    if(!feof(ange_filnamn))
                    {
                        *antal_varor=*antal_varor + 1;        
                    }
                }
                printf("\nNumber of items: %d \n",*antal_varor);
                fclose(ange_filnamn);              
            }

            if(mainmenu==2)
            {
                printf("What name do you want for your new file?\n");
                scanf("%s", filnamn);
                ange_filnamn=fopen(filnamn, "w+");
                printf("File is created!\n");
                *antal_varor = 0;                 
                fclose(ange_filnamn);               
            }
        }
    }

    register_item(struct vara *varor, int *antal_varor)
    {
        printf("Item number:\n");                             
        scanf("%d", varor[*antal_varor].itemnumber);    
        printf("Name:\n");
        scanf("%s", varor[*antal_varor].name);
        printf("Balance:\n");
        scanf("%d", varor[*antal_varor].balance);   
        *antal_varor+=1;
    }

    print_item(struct vara varor[], int antal_varor)
    {
        int i;
        for (i=0; i < antal_varor; i++)
        {
            printf("%d. Item number: %d Name: %s Balance: %d\n", i, varor[i].itemnumber, varor[i].name, varor[i].balance);         
        }
    }

    quit_program(char filnamn[], struct vara varor[], int *antal_varor)
    {
        FILE *fil;
        //printf("%s", filnamn);
        fil=fopen(filnamn, "w+");                                             
        fwrite(varor, sizeof(struct vara), *antal_varor, fil);
        fclose(fil);
    }

    int main(void)
    {
        FILE *ange_filnamn;
        struct vara varor[MAX];
        int mainmenu, menu, antal_varor=0;
        char filnamn[20], filen[30]; 

        open_file(ange_filnamn,filnamn, varor, &antal_varor);

        //Second menu
        while(menu!=7)
        {
            printf("\n");
            printf("1. Register new items to inventory.\n");
            printf("2. Print all items from inventory.\n");
            printf("3. Search for item.\n");
            printf("4. Change inventory.\n");
            printf("5. Sort inventory.\n");
            printf("6. Deregister item from inventory.\n");
            printf("7. Quit.\n");
            scanf("%d", &menu);

            if(menu==1)
            {
                register_item(varor, &antal_varor);
            }

            if (menu==2)
            {
               print_item(varor, antal_varor); 
            }

            if (menu==3)
            {
                printf("test");
            }

            if (menu==4)
            {
                printf("test");
            }

            if (menu==5)
            {
                printf("test");
            }

            if(menu==6)
            {
                printf("test");
            }
            if (menu==7)
            {
                quit_program(filnamn, varor, &antal_varor);
            }
        }
    }

Answer 1

You have an array of structures. The array contains antal_varor number of structures, and each structure contains members (elements) itemnumber, name, and balance.

Before we get started, a little side note: I think your structure definition has some bugs. Based on the way you're using it, I think you want

struct vara
{
    int itemnumber;
    char name[30];
    int balance;
};

But your question was about writing the file out. When you call

fwrite(varor, sizeof(struct vara), *antal_varor, fil);

you are writing out the entire array, all at once, in "binary", which is why you can't read it. If you want to write it out in a more human-readable form, you can do something like this. Here I have an explicit loop over the elements of the array, and each time through the loop, I print out all the members of that element:

int i;
for(i = 0; i < *antal_varor; i++ {
    fprintf(fil, "varor %d:\n", i);
    fprintf(fil, " itemnumber: %d\n", varor[i].itemnumber);
    fprintf(fil, " name: %s\n", varor[i].name);
    fprintf(fil, " balance: %d\n", varor[i].balance);
}

So, first try that. You should find that the output file is perfectly readable.

Now, the problem is that since you wrote the file out in this nicer, more readable format, your code that reads the data back in, that used to use

fread(&varor[*antal_varor], sizeof(struct vara), 1, ange_filnamn);

is not going to work any more. But here is the sort of code you could use to read the new-format file back in. This code reads the file line by line with fgets, figuring out what each line is, and plugging data items one by one into the varor array to rebuild it.

char line[80];
int i = 0;
*antal_varor = 0;

while(fgets(line, sizeof(line), ange_filnamn) != NULL) {
    if(strncmp(line, "varor ", 6) == 0) {
        sscanf(line, "varor %d:", &i);
        if(i >= MAX) {
            fprintf(stderr, "warning: index in file too large\n");
            i = 0;
            continue;
        }
        if(i + 1 > *antal_varor) *antal_varor = i + 1;
    } else if(strncmp(line, " itemnumber:", 12) == 0) {
        sscanf(line, " itemnumber: %d", &varor[i].itemnumber);
    } else if(strncmp(line, " name:", 6) == 0) {
        sscanf(line, " name: %s", varor[i].name);
    } else if(strncmp(line, " balance:", 9) == 0) {
        sscanf(line, " balance: %d", &varor[i].balance);
    } else {
        fprintf(stderr, "warning: unrecognized line in file\n");
    }
}

printf("\nNumber of items: %d \n",*antal_varor);
fclose(ange_filnamn); 

I haven't tested this, so there may be some little mistakes in it, but it should give you the idea.

(Also there are better ways of writing this sort of thing, but they're a little more elaborate or require more infrastructure, so I've stuck to something very simple and understandable, although it's less than robust.)

Answer 2

The commenters on your question have it right.
- What is displayed with printf (and written to a file with fprintf) is ASCII representation of the numbers.
- What is stored in memory (and written with fwrite) is the actual "binary" value.
In C, an int variable always takes up the same number of bytes in memory, regardless of the value stored. That is why your sizeof() works consistently. Reading and writing can be consistently done.

(Note that not all C implementations use the same size int though. It is 4 bytes in the x86 Linux I'm using right now).

When displaying the ASCII representation, the number of ASCII digit characters required depends on the value. So, if reading values in that have been stored this way, you have to 'parse' the text and build up the integer value from the digits read, and in general will be a variable number of digits. (This is what scanf does.) Hence, reading and parsing ASCII could be considered more complicated than just reading in a value stored as binary int that is always the same size.

IMPORTANT: If you are going to read the file as binary, you should open it with the "b" attribute like this:

ange_filnamn=fopen(filnamn, "r+b");

Similary, to open for binary write:

fil=fopen(filnamn, "w+b");