我怎样才能正常地将双点数转换为整数？

Question

I have a Client program by tcp connection that send data to a server. In client I need send a normalized decimal number to server for normalization I Multiplier decimal number to 100,000 then send it to server but I get wrong number in server. for example.

double price;

I set it from Gui to 74.40

cout<<price; ---> 74.40

and when I serial my object I send

#define Normal 100000
int tmp = price*Normal;
oDest<<tmp;

In wireshrk I see that client sent 7439999.

why this happened? how I can pervent this problem?

Answer 1

Don't store anything as a floating point value. Use a rational number instead, or use a fixed point value. Floating point values (like double ) basically "cheat" in order to fix a large range of possible values into a reasonable chunk of memory, and they have to make compromises in order to do so.

If you are storing a financial value, consider storing pennies or cents or whatever is the smallest denomination.

Answer 2

This is due to floating point precision errors. You can add some rounding:

int tmp = (price + 0.5/Normal)*Normal;

Answer 3

由于浮点数无法精确表示十进制数，因此在将其转换为整数时需要四舍五入。

int tmp = price*Normal + 0.5;