Need to read an undetermined amount of integers from stdin into an array

Question

So I\'m writing a practice program that will take integers as input from stdin, load them into an array, sort the array, and then output the results.

I\'ve been struggli

Answer 1

The problem is that sscanf doesn't keep a pointer into the buffer. So every time the code calls sscanf it's just getting the first number from the buffer. The result is an infinite loop.

To fix the problem, you can use the %n conversion specifier. %n returns the number of characters that were used by the conversions. That number (which I call delta in the code below) can be used to update an index into the buffer. Here's how it works, each call to sscanf returns a delta. That delta is added to an index, and the index is used in the expression &buffer[index] to point to the next number in the buffer.

Here's what the resulting code look like

// Load stdin into a buffer
char buffer[100];
if(fgets(buffer, sizeof(buffer), stdin) == NULL)
    Handle_EOForIOError();

// Get a count of the numbers to create the array
int numIntegers = 0;
int index = 0;
int num, delta;
while(sscanf(&buffer[index], "%d%n", &num, &delta) == 1)
{
    numIntegers++;
    index += delta;
}

// Initialize the array with the proper size
int *numbers = malloc(numIntegers*sizeof(int));

// Load the integers into the array
index = 0;
for ( int i = 0; i < numIntegers; i++ )
{
    if (sscanf(&buffer[index], "%d%n", &numbers[i], &delta) != 1)
        ComplainBitterlyAndExit();
    index += delta;
}