signed和unsigned有什么不同？？

[fan_dtor]

定义
int a=-1;
unsigned int b=-1;
printf("%d %d ",a,b);
printf("%u %u",a,b);
结果：
-1 -1 65535 65535
那signed和unsigned还有什么不同？？
a和b在内存中的怎样显示？1111111111111111还是0111111111111111？？
请高手指点，最好可以举个例子和用二进制说明一下.

[qing_li73]

Converting Signed to Unsigned
Objects of signed integral types can be converted to corresponding unsigned types. When these conversions occur, the actual bit pattern does not change; however, the interpretation of the data changes. Consider this code:

#include <iostream.h>

void main()
{
short i = -3;
unsigned short u;

cout << (u = i) << "\n";
}

The following output results:

65533

In the preceding example, a signed short, i, is defined and initialized to a negative number. The expression (u = i) causes i to be converted to an unsigned short prior to the assignment to u.

Converting Unsigned to Signed
Objects of unsigned integral types can be converted to corresponding signed types. However, such a conversion can cause misinterpretation of data if the value of the unsigned object is outside the range representable by the signed type, as demonstrated in the following example:

#include <iostream.h>

void main()
{
short i;
unsigned short u = 65533;

cout << (i = u) << "\n";
}

The following output results:

-3

In the preceding example, u is an unsigned short integral object that must be converted to a signed quantity to evaluate the expression (i = u). Because its value cannot be properly represented in a signed short, the data is misinterpreted as shown.

[fan_dtor]

那我用UNSIGNED和signed的相加结果都一样，打印出来
结果也一样，
如：
unsigned int i=65535;
int a=-1;
printf("%d %u",i+a,i+a);
结果:
-2 65534
那unsigned 和signed用起来还有什么分别？

[daniceexiedong]

每个类型都有自己的用处，和用法。

其实在内存中都一样，主要是外在的表现形式不同。

[crystal_heart]

相同的sign和unsign数字在计算机中的二进制表示完全一样。不同的是他们代表的数字的范围。对于unsign来说，没有负数的概念。16位的机子上，十进制数-1的补码表示为1111111111111111B，如果这数字表示为sign就是-1，如果这数字表示为unsign就是FFFFH(65535)。

[zhang865]

AGREE

[ywpg]

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