Program crashes when a function returns empty

Question

I want to check if my predefined data is in the .dat file that I have. If it so, I print them. If not, my program crashes because the function I wrote has nothing to return.

How do I fix this? How can I check if there is no match and say "No match" and prevent my program being crashed?

struct objectList is for my predefined data. struct database is for the data in .dat file.

struct objectList
{
    double oArea;
    double oLength;
    double oFormFactor;
};

struct database
{
    char name[15];
    double dArea;
    double dLength;
    double dFormFactor;
};

This function reads the file and returns the value if only "area", "length" and "formFactor" matches.

struct database myReadFile(FILE *rPtr, double area, double length, double formFactor)
{
    struct database fromDb = { "", 0.0, 0.0, 0.0 };

    if ((rPtr = fopen("objects.dat", "r")) == NULL)
        printf("Couldn't open the file to read.\n");
    else
    {
        fscanf(rPtr, "%s%lf%lf%lf", fromDb.name, &fromDb.dArea, &fromDb.dLength, &fromDb.dFormFactor);

        while (!feof(rPtr))
        {
            if (fromDb.dArea == area)
                if (fromDb.dLength == length)
                    if (fromDb.dFormFactor == formFactor)
                    {
                        printf("We have found the %s\n", fromDb.name);
                        return fromDb;
                    }

            fscanf(rPtr, "%s%lf%lf%lf", fromDb.name, &fromDb.dArea, &fromDb.dLength, &fromDb.dFormFactor);
        }
    }
    fclose(rPtr);
}

This function prints the values.

void getValues(FILE *gPtr, double area, double length, double formFactor)
{
    struct database objectValues = { "", 0.0, 0.0, 0.0 };

    objectValues = myReadFile(gPtr, area, length, formFactor);

    printf("Object name: %s\n", objectValues.name);
    printf("Object area: %.2lf\n", objectValues.dArea);
    printf("Object length: %.2lf\n", objectValues.dLength);
    printf("Object formFactor: %.2lf\n", objectValues.dFormFactor);
}

main:

int main()
{
    struct objectList myObjectList[4];
    myObjectList[0] = { 9214.00, 417.24, 22.08 };       // Coin
    myObjectList[1] = { 54375.00, 1087.94, 49.97 };     // mp3
    myObjectList[2] = { 12785.00, 550.70, 23.22 };      // toy
    myObjectList[3] = { 100.01, 200.02, 300.03 };       // Random stuff

    FILE *cfPtr;

    if ((cfPtr = fopen("objects.dat", "a +")) == NULL)
        printf("Couldn't open the file\n");
    else
        fclose(cfPtr);

    int i = 2;
    getValues(cfPtr, myObjectList[i].oArea, myObjectList[i].oLength, myObjectList[i].oFormFactor);
    return 0;
}

My .dat file has "toy", "coin", "mp3" but not "random stuff". So when i = 3, my program crashes.

Enable compiler warnings and make them errors! If you do not get a complaint, use a better compiler. — too honest for this site, Oct 11 '15 at 18:32
As you already know you do not return a valid value, why do you have to ask here? — too honest for this site, Oct 11 '15 at 18:33

score 1 · Accepted Answer · edited May 23 '17 at 11:58

The main problem I see with your code is the reading loop, it has mainly two issues

Read: Why is while (!feof(rPtr)) always wrong.
You must check the return value of scanf(), and prevent scanf()'s from overflowing the destination buffer, so the loop condition should be
```
while (fscanf(rPtr, "%14s%lf%lf%lf", fromDb.name, &fromDb.dArea, 
           &fromDb.dLength, &fromDb.dFormFactor) == 4)
```

How about this

int
myReadFile(struct database *db, double area, double length, double formFactor)
{
    FILE *rPtr;
    if ((rPtr = fopen("objects.dat", "r")) == NULL)
        printf("Couldn't open the file to read.\n");
    else
    {
        while (fscanf(rPtr, "%14s%lf%lf%lf", db->name, &db->dArea, 
            &db->dLength, &db->dFormFactor) == 4)
        {
            if ((db->dArea != area) || (db->dLength != length) || 
                (db->dFormFactor != formFactor))
            {
                continue;
            }
            fclose(rPtr);
            return 0;
        }
    }
    fclose(rPtr);
    return -1;
}

And in the main function

struct database result;
if (getValues(&result, myObjectList[i].oArea, 
    myObjectList[i].oLength, myObjectList[i].oFormFactor) == 0)
{
    fprintf(stderr, "%s\n", result.name);
}

Thanks. Very smooth and what I wanted. Should I also close the file when the function returns 0? — massakrienen, Oct 12 '15 at 06:14
Yes you should!!! I missed that, I will add it to the answer for completeness. Oh also you don't need to pass `rPtr` to the function, perhaps pass the path to the file instead, which would make the function more reusable — Iharob Al Asimi, Oct 12 '15 at 06:29

Program crashes when a function returns empty

1 Answers1