我在这个网站上搜索了一个答案,发现许多对未签名/签名比较的回复,但是这个问题是只比较了无符号参数,但它仍然很有趣.
以下代码的问题在于第一个if-statment不会发生("hello"),而第二个("world")就是这样.我已经解释为在if-statment 内部进行的计算会生成一个负数但是保存到变量的结果完全相同的计算不会(即使结果被保存到有符号变量).
使用的编译器是gcc 4.4.
unsigned short u16_varHigh;
unsigned short u16_varLow;
unsigned short u16_Res1;
signed short s16_Res1;
u16_varHigh = 0xFFFF;
u16_varLow = 10;
u16_Res1 = u16_varLow - u16_varHigh; // response is 11 as expected
s16_Res1 = u16_varLow - u16_varHigh; // response is 11 as expected
// Does not enter
if( (u16_varLow - u16_varHigh) > (unsigned short)5 )
{
printf( "hello" );
}
// Does enter
if( (unsigned short)(u16_varLow - u16_varHigh) > 5 )
{
printf( "world" …