c - sscanf doesn't move, scanning same integer everytime

Question

I have a string that has ints and I'm trying to get all the ints into another array. When sscanf fails to find an int I want the loop to stop. So, I did the following:

int i;
int getout = 0;
for (i = 0; i < bsize && !getout; i++) {
    if (!sscanf(startbuffer, "%d", &startarray[i])) {
        getout = 1;
    }
}
//startbuffer is a string, startarray is an int array.

This results in having all the elements of startarray to be the first char in startbuffer. sscanf works fine but it doesn't move onto the next int it just stays at the first position.

Any idea what's wrong? Thanks.

Answer 1

The same string pointer is passed each time you call sscanf. If it were to "move" the input, it would have to move all the bytes of the string each time which would be slow for long strings. Furthermore, it would be moving the bytes that weren't scanned.

Instead, you need to implement this yourself by querying it for the number of bytes consumed and the number of values read. Use that information to adjust the pointers yourself.

int nums_now, bytes_now;
int bytes_consumed = 0, nums_read = 0;

while ( ( nums_now = 
        sscanf( string + bytes_consumed, "%d%n", arr + nums_read, & bytes_now )
        ) > 0 ) {
    bytes_consumed += bytes_now;
    nums_read += nums_now;
}