fprintf printing a bunch of NULLs at the beginning

typedef struct record
{
    float field1;
    char *name;
} record;

void printRecordsTo(record **s, char *fileName, int size)
{
    initializePrinter(fileName);
    int i = 0;
    while (i < size)
    {
        printRecordToFile(s[i]);
        i++;
    }
    closePrinter();
}

static int delete = 0; // TODO: Remove
void printRecordToFile(record *r)
{
    if (!file)
    {
        puts("Printer not initialized");
        exit(1);
    }
    printf("%d %s", delete ++, toString(r)); // prints all correctly to stdout
    fprintf(file, "%s", toString(r));        // includes many NULLs
}

char *toString(record *s)
{
    float field1 = s->field1;
    int len = 4;
    char *field1Str = malloc(len + 1);
    snprintf(field1Str, len + 1, "%f", field1);
    char *name = s->name;
    char *buf = malloc((1024) * sizeof(char));
    snprintf(buf, 1023, "%s%s%s%s%s\n", "(", name, ", ", field1Str, ")");
    return buf;
}

I can’t figure out why many NULLs are being printed by the fprintf for large files (of size ~1000 records). The function works fine for the small files (of size ~20 records) I used. I tested it against normal printf which prints the string representations of records correctly.

>Solution :

1. Drop toString() function from source, it’s redundant.

2. Use below statements instead in printRecordToFile()

    printf ("%d (%s, %f)", delete++, r->name, r->field1);
    fprintf (file, "(%s, %f)", r->name, r->field1);

3. Use meaningful names for structure attributes/members.

4. If you’re still seeing garbage values, then perhaps you need to sit with a debugger to find out where structure data is being corrupted. With the info at hand we can only guess.

5. Use Valgrind to trace memory error & leaks. It’s a pretty nifty tool for C programmers.