怪了, 程序请教

只看该作者 · 2009-8-5 10:39

record_data_num=((data_buffer[0]-0x30)*1000000
                        +(data_buffer[1]-0x30)*100000
                        +(data_buffer[2]-0x30)*10000
                        +(data_buffer[3]-0x30)*1000
                        +(data_buffer[4]-0x30)*100
                        +(data_buffer[5]-0x30)*10
                        +(data_buffer[6]-0x30)*1);
record_data_num 是unsigned long 类型
data_buffer是unsigned char 类型

data_buffer[0]='0';
data_buffer[1]='0';
data_buffer[2]='6';
data_buffer[3]='5';
data_buffer[4]='5';
data_buffer[5]='2';
data_buffer[6]='8';
即0x0000fff8

而运行结果, record_data_num 是4294967288  即0xfffffff8
这是为何? 麻烦指点,谢谢

只看该作者 · 2009-8-5 11:49

分成几步，做加法，试试看。编译器有时候不太聪明。
record_data_num = (data_buffer[0]-0x30)*1000000;
record_data_num += (data_buffer[1]-0x30)*100000;
record_data_num += (data_buffer[2]-0x30)*10000;
record_data_num += (data_buffer[3]-0x30)*1000;
record_data_num += (data_buffer[4]-0x30)*100;
record_data_num += (data_buffer[5]-0x30)*10;
record_data_num += (data_buffer[6]-0x30)*1);