C++ 演练 cout.setf(ios::fixed); 和 cout.precision();
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C++ Walkthrough cout.setf(ios::fixed); and cout.precision();
提问by Ali
/* Problem 38 */
#include <iostream>
using namespace std;
class abc {
double n;
public:
abc() { n = 67.5; cout << "1\n"; }
abc(double num) { set(num); cout << "2\n"; }
double get() const { cout<<"3\n"; return n; }
virtual void set(double num) {
if (num < 10)
n = 10;
else if (num > 100)
n = 100;
else
n = num;
cout << "4\n";
}
};
class def: public abc {
double m;
public:
def() { m = 6.2; cout << "5\n"; }
def(double num1, double num2): abc(num1) {
set(num2 - abc::get()); cout << "6\n"; }
double get() const {
cout << "7\n"; return m + abc::get(); }
void set(double num) {
if (num < 10 || 100 < num)
m = num;
else
m = 55;
cout << "8\n";
}
};
void do_it(abc &var, double num)
{ cout << var.get() << '\n';
var.set(num);
cout << var.get() << '\n';
}
int main()
{ abc x(45);
def y(2, 340);
cout.setf(ios::fixed);
cout.precision(3);
do_it(x, 200);
do_it(y, 253);
cout << x.get() << '\n';
cout << y.get() << '\n';
return 0;
}
With the above code I just wanted to know what below two lines will really do in the above code
有了上面的代码，我只想知道下面两行在上面的代码中真正会做什么
cout.setf(ios::fixed);cout.precision(3);
cout.setf(ios::fixed);cout.precision(3);
Please do not just give me answer some explanation would be so appreciated because I'm doing a walkthrough to prepare for my final exam tomorrow.
请不要只是给我答案，因为我正在做一个演练，为明天的期末考试做准备。
I searched and some source says it is to set flags but really I don't get what is the concept of it and how it works
我搜索了一些消息来源说这是设置标志但实际上我不明白它的概念是什么以及它是如何工作的
回答by bjhend
cout.setf(ios::fixed)
makes cout print floats with a fixed number of decimals and
使 cout 打印浮点数具有固定的小数位数和
cout.precision(3)
sets this number to be three.
将此数字设置为 3。
For example, if you got a
例如，如果你有一个
double f = 2.5;
then
然后
cout << f;
will print
将打印
2.500
回答by Erwald
Great documentation about how to format your output : Output formatting
关于如何格式化输出的优秀文档：输出格式
It's always usefull when you're trying to do a command-line UI.
当您尝试执行命令行 UI 时，它总是很有用。
回答by Erwald
#include<iostream>
using namespace std;
int main(){
float large = 2000000000;
cout << large;
return 0;
}
The output will be in scientific notation as:
输出将采用科学记数法，如下所示：
2e+009
In order to get the value as it is you should use cout.setf(ios::fixed)
为了获得原样的价值，您应该使用 cout.setf(ios::fixed)
#include<iostream>
using namespace std;
int main(){
cout.setf(ios::fixed);
float large = 2000000000;
cout << large;
return 0;
}
The output will be as it is with default precision which is 6 for float.
输出将与默认精度相同，浮点数为 6。
2000000000.000000
You can set the precision in the above code as:
您可以将上述代码中的精度设置为：
cout.precision(7);
.....
.....
回答by TheEngineer
It's similar to including the manipulation library:
include :
它类似于包含操作库：
include ：
<iomanip>
And then using the following functions
然后使用以下功能
cout << fixed << showpoint;
cout << setprecision(3);
