You can also get rid of one if block and the l_temp_1_int variable:
Code:
while ( (l_i <= l_temp_2_int ) && (l_while_stop_bool == false) )
{
	l_temp_1_int = 0;
	l_chr = str_getchr(l_temp_1_str, l_i);
	
	if ((l_chr >= 'A' && l_chr <= 'Z') || 
	    (l_chr >= 'a' && l_chr <= 'z') || 
	    (l_chr >= '0' && l_chr <= '9')  )
	{
		l_i++;
	} else {
		l_while_stop_bool = true;
	}
}

Always learn from history, to be sure you make the same mistakes again...