Question

I’m looking to have fscanf identify when a potential overflow happens, and I can’t wrap my head around how best to do it.

For example, for a file containing the string

**a**bb**cccc**

I do a

char str[10];
while (fscanf(inputf, "*%10[^*]*", str) != EOF) {

}

because I’m guaranteed that what is between ** and ** is usually less than 10. But sometimes I might get a

**a**bb**cccc*

(without the last *) or even potentially a buffer overflow.

I considered using

while (fscanf(inputf, "*%10[^*]", str) != EOF) {

}

(without the last *) or even

while (fscanf(inputf, "*%10s*", str) != EOF) {

}

but that would return the entire string. I tried seeing if I could check for the presence or lack of a *, but I can’t get that to work. I’ve also seen implementation of fgets, but I’d rather not make it complicated. Any ideas?

Answer 1

I’m not clear on exactly what you want. Is it to skip over any number of stars, and then read up to 9 non-star characters into a buffer? If so, try this:

void read_field(FILE *fin, char buf[10])
{
    int c;
    char *ptr = buf;
    while ((c = getc(fin)) == '*')
        /*continue*/;
    while (c != '*' && c != EOF && ptr < buf+9)
    {
        *ptr++ = c;
        c = getc(fin);
    }
    *ptr = '\0';
    /* skip to next star here? */
}

You will note that I am not using fscanf. That is because fscanf is nearly always more trouble than it’s worth. The above is more typing, but I can be confident that it does what I described it as doing.