__LINE__ is a preprocessor macro which turns into whatever line number it's on. Like so:
Code:
#include <stdio.h>
int main( void )
{
printf("line: %d\n", __LINE__ );
printf("\n");
printf("line: %d\n", __LINE__ );
printf("line: %d\n", __LINE__ );
printf("line: %d\n", __LINE__ );
printf("\n");
printf("\n");
printf("line: %d\n", __LINE__ );
return 0;
}
So, when used as I've illustrated, you can use it to display the line number in your program. Combine with whatever variable you're trying to display, you can end up seeing what the value of that variable is when you're on a given line number in your program. Not the greatest debugger, but it'll work in a pinch.
Quzah.